ISCHAEMIA : A HYPOTHESIS FOR THE GENESIS OF

AGANGLIONIC BOWEL.

Richard Earlam, M.A., F.R.C.S.

ISABELLA FORSHALL ESSAY PRIZE 1968

CONTENTS

Page

Introduction - are achalasia of the oesophagus, Hirschsprung's Idisease and the rare aganglionic megaduodenumsimilar diseases ?

Anatomical distribution 3

Epidemiology 5

Discussion of anatomy and epidemiology 9

Normal nerve supply of the bowel 12

Abnormalities of the nerve supply 16

Abnormalities of the muscle 18

Previous aetiological theories - I general 19

II Chagas* disease 21

III extrinsic nerve lesions 22

IV neural crest lesions 24

Summary of previous aetiological theories - 26suggestion that the lesions are distributed accordingto the arterial blood supply

Experimental ischaemia as a cause of intestinal atresia 26

Temporary Ischaemia 29

Early embryological development of gut 32

Embryology of oesophageal atresia and tracheo-oesophageal fistula 35

Page

Transitional aganglionlc zone between atretic 36and normal bowel

Epidemiology of atresia and stenosis 37

Discusson of epidemiology 42

Muscle and ganglion cell changes in scleroderma 43

Arterial lesions 44

Hypochlorhydria of the stomach in achalasia 45

Summary 4i

Bibliography 49

OBITUARY

habtlla Farshall

Obituaries of any doctors 'Vlillbe considered for pvttifatifnprovided thai ike donors haveworked m ilit UmieiKingdom for a large partofihtrirf<tr?er, Obituaries mustt>? submitted exclusively toihs BMJ and should be up10 ad<Htt 300 UXirds long;they ShOtM be sent withinnxttMttthSf and preferablywuhin three months, of death."Self-written" obituaries are

ISABELLA FORSHALLCHM, FRCS, FRCSED

Isabella Forshall was one of the pioneers whose workdid much to establish paediatric surgery as a recog-nised branch of surgery in the United Kingdom. It isremarkable that she should have done so at a time whenwomen were not expected to achieve distinctions in theprofessions and when the surgical establishment didnot encourage the development of subspecialties.

Isabella's childhood was spent in affluent surround-ings in west Sussex. She was educated privately athome and never went to school. Her education, nodoubt influenced by her mother, who had read classicsat Girton in the 1890s, imbued her with a keenappreciation of art and literature and particularlypoetry. It is perhaps surprising that a young woman ofher time and background should have embarked on acareer in medicine. When asked about the family'sattitudes to her ambition she would say that she hadbeen expected to make the observance of her socialresponsibilities her first priority and, although neverencouraged to think of a career, was never activelydiscouraged.

Isabella was appointed house surgeon at the RoyalLiverpool Children's Hospital in 1929 and later atAlder Hey Children's Hospital and worked at thesehospitals until her retirement in 1965. In 1939, whileretaining her registrar post, she became honorary-assistant surgeon at Birkenhead and Wirral Children'sHospital and Waterloo General Hospital. In 1942 shebecame an honorary surgeon at the Royal LiverpoolChildren's Hospital.

It was not until the end of the war that Isabella wasable to realise her ambitions for paediatric surgery. Shegathered around her a group of young people inpaediamc surgery and in the associated specialties,whom she fired with her own enthusiasm. This resultedin considerable advances in the surgical treatment ofchildren and in the foundation in 1953 of the Liverpoolneonatal surgical centre. During the first six years of itsactivity the mortality of infants with surgically treat-able congenital abnormalities in the Liverpool regionfell from 72% to 24%, and soon afterwards the Ministryof Health published a report on surgery of the newbornthat strongly recommended the establishment ofsimilar units in all regions.

These achievements brought Isabella widespreadrecognition nationally and internationally. In 1958 shebecame the second president of the British Associationof Paediatric Surgeons; the next year she was electedpresident of the paediatric section of the Royal Societyof Medicine. She was president of Liverpool MedicalInstitution in 1963, was elected an honorary member ofthe British Association of Paediatric Surgeons and ofthe British Paediatric Association, and in 1970 wasawarded an honorary degree of master of surgery fromthe University of Liverpool. Despite having such adistinguished career she had no personal ambition andwould give to her associates much more credit thanthey sometimes deserved for joint achievements; shefought only for the better care of children.

Those who enjoyed her friendship quickly learnt ofher warmth, her delightfully mischievous humour, herabhorrence of pomposity, and her concern for all,particularly the deprived. It was this concern thatcaused her to be among the first to embark on the moreenlightened approach to the needs of children inhospital that today is the norm: in her early days

parental visiting was greatly restricted and awarenessof children's emotional needs was totally lacking.

Throughout her busy working life she devoted everyspare moment to her garden, which was always a joy tosee and where she loved to entertain on a summerevening. She was delighted to retire to her belovedSussex.-JR.

Isabella Forshall, formerly senior paediamc surgfon ai RoyalLiverpool and Alder Hey Children's Hospitals, dud 10 Augustage 88. Bom west Sussex; studied medicine at London School ofHospital for Women (MB, BS 1927).

BMJ VOLUME 300 6 JANUARY 1990

INTRODUCTION

Hirschsprung's disease and achaiasia of the oesophagus are similar because

the ganglion cells in Auerbach's plexus are either absent or fewer than normal.

The aetiology of both diseases is unknown but the surgical treatment alleviates

the symptoms satisfactorily. Textbooks of surgery have emphasized that they

are different, because in Hirschsprung's disease the dilated bowel is normal and

the narrow segment has no ganglion cells but, in achaiasia of the oesophagus,

the dilated gut contains few or no ganglion cells. They are the same type of

lesions because the bowel is aganglionic but the gut reacts differently in each

part to this denervation. All agangiionic bowel is dilated except for the narrow

segment"in Hirschsprung's disease and the lower end of the oesophagus in achaiasia.

In megacolon, caused by Chagas" disease, there is a similar loss of ganglion cells

and in those cases of Hirschsprung's disease which persist untreated into adult

life, there is no narrow segment of obstruction (186, 233). This narrowed bowel,

in which no co-ordinated function can occur, is caused by the failure of circular

muscle relaxation after denervation and by the inability of the propulsive power

of the proximal gut to dilate it. The dilatation in achaiasia is inexplicable if

the competence of the gastro-oesophageal function is thought to be due to a flap-

valve or pinch-cock mechanism of the diaphragm rather than a physiological

sphincter (53,59,85). The denervation produced by the lack of ganglion cells

causes a lack of co-ordinated peristalsis in the body of the oesophagus and a failure

of sphincteric relaxation. The physiological sphincter can be forced open by a

column of liquid when the hydrostatic pressure is high but not by a normal

swallow. Dilatation follows the obstruction. The sphincter is normally closed

and the pressure may temporarily but never permanently open it, so that free

reflux can occur from stomach to oesophagus. This type of sphincter does not

exist in the colon or rectum to explain Hirschsprung's disease.

This essay reviews the present knowledge of the diseases and suggests a unifying

hypothesis for the cause of aganglionic bowel. The rare aganglionic megaduodenum

is also discussed so that a spectrum of lesions which include achalasia of the

oesophagus, aganglionic megaduodenum and Hirschsprung's disease can be

considered together. Many unconnected facets of the diseases are clarified

and made understandable by such a hypothesis, which the majority of the evidence

substantiates. However this is no conclusive proof that the ideas are correct and

future experimental work, based on the hypothesis, remains to be done.

ANATOMICAL DISTRIBUTION

The term agemglionic bowel is used in American literature and has the advantage

that achalasia of the oesophagus, aganglionic megaduodenum and Hirschsprutig's

disease can all be discussed under one heading, but it has the disadvantage of a

neologism and is inexact when a few ganglion cells remain.

Sir Arthur Hurst first suggested that achalasia of the oesophagus might be a

peristaltic disorder because of absent ganglion cells (125), but this was first found

by Rake in 1927 (221). The body of the oesophagus is affected more than the

lower end and the gastro-oesophageal junction (280). The ganglion cells at the

lower end may be reduced in number or normal even when the body of the oesophagus

contains no ganglion cells (3, 45, 161). The cardiac end of the stomach in achalasia

may also contain fewer cells (28, 221). A re-examination of the material used by

Cassella (45) in his study at the Mayo Clinic by the author showed this ganglion cell

loss in some of the cases.

In 1933 the first patient with aganglionic megaduodenum was described (138) and

by 1955 the number had increased to 32 (14). Megaduodenum is rare and is

usually said to be caused by compression of the gut by mesenteric vessels but

histological examination is rarely done. There is no sufficient information available

to describe the distribution or the extent of the lesions.

Considerably more information is available in Hirschsprung's disease about the

distribution of aganglionic bowel (9, 37), which was first described by Tittel in

1901 (268) although this is usually ascribed to Dalle Valle (63). In the majority,

a short segment below the pelvic colon is affected but, in a minority, longer

segments of colon are involved. Bodian (26, 27) gives the percentages as 82%

for the "short" segment below the pelvic colon, 17% for the "long" segment

extending above this level and \% involving the small intesiine (27). 55 cases

of total colonic involvement have now been described (254) and 31 cases involving

both the entire colon and the small intestine up to the duodenal jejuna! flexure

are documented (277). A very rare "mid-zonal" variety occurs (27, 109), in

which the aganglionic segment is confined to the pelvic colon but the bowel

above and below is normal.

Most of the gut may lose ganglion cells but aganglionic bowel is most frequent at

both ends of the gastro- intestine I tract. In more extensive cases either end is

affected and the disease process extends inwards either to the stomach from the

oesophagus or to the colon and small intestine from below.

In two types, megaduodenum and the "mid-zonal" Hirschsprung's disease, there

is an intermediate segment without the ends involved.

EPIDEMIOLOGY

The distribution of aganglionic bowel in populations throughout the world enables

individual factors such as race, age, sex or associated diseases to be compared

and apparent differences may suggest aetiologies. In the absence of complete

epidemiological studies, geographical, racial, sexual and environmental factors

can only be incompletely assessed from patients seen in hospital.

The geographical distirubtion must be assessed from the isolated case reports and

most series of surgical patients or those treated by dilatation represent a biased

selection and a minimal incidence because the total population at risk is not

examined accurately.

Willis described the first case of achalasia in 1674 (285), and by 1920 more than

1200 had been described (43). The Mayo Clinic have published two separate

series of 691 (192) and 601 patients (208). The steady increase may be true due

to a rise in the incidence or apparent because of more patients reported. But

the number diagnosed has not increased appreciably because no real advance in

diagnostic techniques have been made since the advent of radiology. The only

epidemiological study of incidence and prevalence comes from the Mayo Clinic,

Rochester, Minnesota, where the prevalence appears to be about I :IOO,000 with

no changes over the last thirty years (79). These figures are based on small numbers

in a small community but are complete.

Only thirty-two patients with agangl ionic megaduodenum have been described,

therefore no epidemiological study has been conducted (14). Those from Brasil

have not been included in this number (219). Far more work has been done on the

epidemiology of Hirschsprung's disease. In London there is an incidence of

between I : 2000 and I : 10,000 newborn children (26) and in Bremen, Germany

I : 12,000 (9). A calculation of the figures from the Neonatal Surgical Unit

In Liverpool, serving a population of three million, with a birth rate of 60,000

per annum, suggest also an incidence of I : 12,000 live births (92, 227).

No figures of prevalence in the population have been given but since the survival

rate after successful treatment in this disease is high, the prevalence of

Hirschsprung's disease must be far higher than achalasia.

Factors of race, geography and species:

Achalasia is well documented in European and North American literature in

Caucasians but it is more rarely described in other cases. In one study there

were twelve Negroes out of 123 patients with achalasia in Chicago (167). In

South Africa only seven cases have been described in Negroes (151) and in

North Africa eight (41, 47). Most of the Negroes affected were adults but one

Negro infant with achalasia has been reported (223). The disease exists in

Indians (5) and Japanese (205). In Europe, achalasia has been reported from

Budapest (28), Coimbra (43), Graz (164), Leipzig (122), Liverpool (228),

London (15, 83), Louvain (273), Lyons (237), Malmo (187), Moscow (271),

Munich (299), Oslo (123), Oxford (6, 22), Wroclaw (145). Achalasia has also

been described in dogs, occurring spontaneously in more than fifty of which the

breed most affected is Alsation (81, 132, 133).

Hirschsprung's disease also shows no specific geographical or racial bias. Since

the original description by Hirschsprung from Denmark (130) it has been described

in most races and cities including Peking (51) and Cairo (98). A series from

South Africa confirmed that it occurred in Whites, Cape-coloured, and Negroes

(102). Megacolon without histological confirmation has occurred in the cat (62)

and in pigs (152) but not in the dog. Histological confirmation is available

in the large series of inbred mice with congenital megacolon described from

Australia (23, 70).

Sex and age factors :

Sex differences in achalasia were not apparent in two series (167, 299), although

in one large adult series males predominated by 327 to 274 (209) and in one group

of children males predominated by 16 to II (213). At St. Thomas Hospital, London,

males predominated over females below the age of fifty but above this age the

ratio was reversed (15). No definite conclusion can be drawn from the sex

incidence because the figures usually given are not adjusted to the age and sex

distirubtions in the general population. The only available epidemiological

study shows a preponderance of females (79).

In Hirschsprung's disease Bodian and Carter showed that boys predominated over

girls by 3.6 : I but that when "short" segment disease was considered alone it was

5 ; I. However in the "long" segment disease there was almost an equal

incidence (26, 27). Age is an important factor in the distribution of aganglionic

lesions. In the oesophagus the usual age presentation is between 45 and 55,

although the onset of symptoms is a decade earlier (208, 209, 212). Approximately

\Q% have symptoms before the age of 14 (191), and the disease exists in the

neonate (228), the first case being described in 1906 (179). The true incidence of

the congenital or infantile type is probably less than 5% of the total. There were

three cases in Liverpool in a ten year period during which 74 adults were

treated (228).

8

In aganglIonic megaduodenum symptoms occur usually between 17 and 74 with

a mean age of 40 (14) and only one case discovered at birth has been described

(138). In Hirschsprung's disease the mafority are diagnosed soon after birth but

occasionally they may present later (186, 198, 233).

The genetical factors involved are difficult to assess. Three families with achalasia

occurring in two siblings have been described (201, 267, 270) and one with three

brothers affected (74), otherwise no familial incidence is noteworthy. In

Hirschsprung's disease numerous siblings and successive generations are recorded

but Bodian and associates in an analysis of over 200 cases could find no simple

hypothesis as to the nature of the genetic factors (26). The association of

Hirschsprung's disease with achalasia has been described in two patients in a large

series (212) but large series of Hirschsprung's disease contain no achalasic

patients (259). No significant associated diseases are described with achalasia

(209) or aganglionic megaduodenum but in 204 patients with the colon affected

there were other malformations in ten, of which three had mongolism (26). Only

this last association seems to be significant but in the literature it has only been

reported in 19 cases (104). A disturbance of bladder function possibly connected

with aganglionic gladder was found in 5% of children with this disease (257) but

a very detailed study of the vesical ganglia has shown normal ganglion cells in the

bladder and not a single case of megaureter in 278 cases (174).

DISCUSSION OF ANATOMY AND EPIDEMIOLOGY

The anatomical distribution of aganglionic bowel obviously affects the intestinal

tract at both ends of which the lower end is more susceptible. When the disease

involves a greater length of bowel it usually affects one end primarily and then

extends inwards. Megaduodenum and the rare "mid-zonal" variety of

Hirschsprung's disease are two exceptions. The anatomical distribution is similar

to that of intestinal atresia where oesophagus and rectum are most frequently

atretic. The cause of the anatomical distribution is not known but the lesions

are distirubted according to the arterial blood supply. The oesophagus is supplied

above by branches from the inferior thyroid artery, below by branches from the

left gastric and inferior phrenic arteries, and in the middle by two to three branches

from the aorta and bronchial arteries (189). When the left gastric artery is

severed to facilitate gastric mobilisation, the lower oesophagus may be severely

devascularised and the anastomosis between the bronchial artery and the inferior

phrenic arteries may be insufficient (245, 258). The inferior phrenic arteries may

be sufficiently large enough to play an important role in collateral circulation (189)

but they themselves arise from the left gastric artery in about 2% of cases in which

case division of the left gastric artery would be more likely to cause necrosis (189).

Whenever the blood supply is poor, such as in arteriosclerosis, abnormal arterial

distirbutions or blockage of one of the main arterial vessels the middle of the

oesophagus is most susceptible to ischaemia (258). The necrotic area will extend

to involve the lower end of the oesophagus and possibly the stomach, if the blood

supply is more severely compromised.

10

The second part of the duodenum is normally well supplied with blood from the

coeliac axis and the superior mesenteric artery through the superior and inferior

pancreatico-duodenal arteries and the anastomosis between them, but is

susceptible if either one or both of the main aortic vessels is obstructed.

The rectum is supplied by the terminal branches of the superior haemorrhoidal.

artery and there is an anastomosis at the lower end with the branches of the internal

iliac artery. If the whole colon and terminal ileum are involved, the distribution

is that of the inferior mesenteric and sigmoid branches. When the lesion extends

to the duodeno-}e}unal flexure, such an area is supplied by the superior and

inferior mesenteric arteries.

It is suggested that the anatomical distirubtion of aganglionic bowel is based on

its blood supply. The bowel affected also has a distribution similar to that of

the atresias. The arterial supply is contained in vascular pedicles, which,

although apparently fixed, were at one stage of intra-uterine life free, mobile

and involved in replacing thegut in its adult position. If they are susceptible to

rotation, it is conceivable that they could be obstructed at this stage.

The epidemiology of the disease was assessed by searching through the reports of

isolated cases and large series of aganglionic bowel. Apart from the epidemiological

studies in achalasia (79) and Hirschsprung's disease (9, 26) showing the true

incidence, the findings represent only a minimal incidence. A case report

indicates the existence of the disease in a population but not its true frequency

unless the disease has been excluded from the whole population at risk.

Hirschsprung's disease is more common than achalasia and has an incidence of

about I : 12,000. Achalasia has an incidence of I : 100000 and occurs in adults

between the ages of 35 and 45. Hirschsprung's disease may very rarely not present

until adult life, but 5% of achalasia patients have symptoms in early childhood.

There is no geographical nor racial limitation to the diseases because they have

been described in most lands and races, and other species than man are affected.

The sex differences in achalasia are not significant, whereas in "short" segment

Hirschsprung's disease the male predomination is real. Bodian suggests that this

may be associated with the advanced development that a female child has,

compared with a male, at birth but this does not help to find the aetiology. There

is no genetical basis for achalasia in humans although there may be in dogs. But

there may be a genetical basis for Hirschsprung's disease, which is supported by

the evidence of numerous siblings and families as well as the inbred strain of

mice. The mechanism of such hereditary factors is not apparent.

Aganglionic bowel has a random distribution and there are no definite causative

factors that can be deduced from the present available epidemiology.

12

NORMAL NERVE SUPPLY OF THE BOWEL

The intestine throughout its whole length is a hollow muscular tube with an

inner circular and an outer longitudinal muscular layer. In the wall of the

gut lies the intrinsic nervous system of Auerbach's intermuscular and Meissner's

submucous plexus. The extrinsic nervous system is the cranial parasympathetic

distributed in the vagus, the pelvic parasympathetic and the sympathetic nervous

system. The vagus motor fibres, originating in the dorsal motor nucleus, are

pre-ganglionic and synapse with the ganglion cells in Auerbach's plexus, which

relay post-ganglionic fibres. The pelvic para-sympathetic fibres have similar

connection with cells in the colon and rectum. The sympathetic fibres have a

ganglion outside the gut and post-ganglionic fibres pass to the gut wall. The

final termination of these sympathetic fibres is unknown. They may either

(I) end on blood vessels, (2) directly innervate smooth muscle cells or

(3) synapse with the ganglion cells. In the latter case the post-ganglionic

fibres belong to the ganglion cells of Auerbach's plexus and a tri-neuronal theory

of distribution for the sympathetic must be postulated (169). In the intestinal

wall, six neuronal plexuses have been described, but Auerbach's and Meissner's

plexuses are the most important (129). Between the layers of muscle lies a

network of nerve fibres at the junction of which lie Auerbach's plexuses. These

consist of about 40 ganglion cells also called enteric neurones (108), interstitial

cells of Cajal, fibroblasts, pre-gangl ionic non-medu Hated para-sympathetic,

post-ganglionic sympathetic fibres, numerous inter-connecting fibres of the

ganglion cells (129), and occasional sensory organs (143, 165, 250).

13

Meissner's plexus is situated in the submucous layer and is not so large. There

is usually no Meissner's plexus in the oesophagus (108, 166, 222, 253) although

one illustration in Cassella's thesis demonstrates it. The author has never seen

it in the oesophagus except for this one illustration. It certainly exists in the

colon and the rectum.

Dogiel (76) described three types of ganglion cells, all recognised by their large

size and nucleus, cytoplasm with dark granules and their processes. Dogiel

Type I is a rnuitipolar cell with short dendrites and has one predominant axone

which may end on muscle, although even electronmicroscopy can not demonstrate

this convincingly. This cell is more common in the rectum and the oesophagus

and is definitely motor in function (165). Dogiel Type II is a sensory cell,

multipolar with long dendrites passing to the mucosa. It exists in the small

intestine with Type I but is not seen in the oesophagus or rectum. Dogiel Type III

is similar to Type II but has large dendrites which do not anastomose. This

subdivision is based on the appearances after silver staining, and the different

types may possibly be artefacts of this method. The interstitial cells of Cajal

are now thought to be fibroblasts on the evidence provided by the electronmicroscope

(226). The majority of the fibres are interganglionic connections of the intrinsic

nervous system and also connect Auerbach's plexus with Meissner's. The

generally accepted view is that Auerbach's plexus is predominantly motor and

Meissner's sensory. The motor fibres to muscle are the processes of Type I

ganglion cells, although an intermediate fibre plexus as well as the interstitial

cells of Cajal was originally suggested as an intermediate station. The

anatomical basis for a local reflex arc definitely exists independent from the

extrinsic nervous system (165, 166, 276) and this has also been demonstrated

14

physiologically (16, 33). Six months after a vagotomy in dogs the oesophagus

may still have an intact local reflex (38, 139, 150).

The extrinsic nerve supply is predominantly parasympathetic with the sympathetic

playing an unknown but relatively unimportant role. The vagus is said to supply

the gut as far as the splenic flexure (105), based on experimental work in cats

and dogs showing degeneration to this level after section of the vagal trunks (24).

Such degeneration has also recently been confirmed (242) but the number of

fibres ending in this region is very small. The distribution of the vagus on the

intestinal wall ends at the pylorus and the route of any further fibres to the colon

must be in the gut wall. The distal part of the gut is supplied by the pelvic

para-sympathetic but the exact distribution is unknown. Evidence shows that

the motor fibres of the vagus may go no further than the pylorus (272) where

their distribution on the outer wall of the gut ends. The evidence from comparative

anatomy in the chick may be pertinent because the vagus supplies the gut to the

pylorus and then the nerve of Remak passing upwards supplies the gut distal to

this point (40, 294, 295). A further fact, not sufficiently emphasized, is that

the vagus is predominantly sensory and not motor (4, 134) and most of the fibres

are non-myelmated (46, 134) with less than \O°/o efferent at the diaphragm (4).

In the cat there are approximately 3000 motor fibres at the diaphragm (4) compared

with 5 million ganglion cells in Auerbach's and 15 million in Meissner's

plexus (239). If the vagal pre-ganglionic fibres end on Auerbach's plexus

distal to the pylorus, the distribution must be very sparse in proportion to the

vast numbers of ganglion cells. More pre-gangl ionic fibres end on the cells of

Auerbach's plexus in the oesophagus and stomach than in the small intestine.

If structure is to be related to function this will explain why the oesophagus and

15

the stomach are the only parts of the gut with a true coordinated peristaltic

wave whereas the small intestine has an intrinsic thythm with a frequency

dependent on the inherent gradient in the gut. There is also evidence that

the ganglion cells decrease in number from the pylorus to the ileo-caecal

region (173).

The motor fibres of the vagus arise in the dorsal motor nucleus of the vagus.

The central connections of the sensory fibres are in the tractus solitarius.

Retrograde degeneration has been demonstrated after peripheral nerve section

in the dorsal motor nucleus of the vagus (19, 97, 194, 260, 292). The striated

muscle of the oesophagus is supplied by fibres from the nucleus ambiguus.

Retrograde degeneration studies have also shown that the caudal part of this

nucleus Is the source of these fibres (97, 261, 171). In the dog these non-

medullated pre-ganglionic fibres do not pass directly to the striated muscle but

relay in the cells of Auerbach's plexus (120). Evidence on this point is not

available in humans but Auerbach's plexus has been seen in the predominantly

striated muscle part of the oesophagus by the author.

Originally the pathological changes described in achalasia and Hirschsprung's

disease were confined to the ganglion cells of Auerbach's plexus. Recently

more detailed pathology of the changes in Auerbach's and Meissner's plexuses,

the extrinsic nerves, their central connections and the muscles has become available.

16

ABNORMALITIES OF THE NERVE SUPPLY

Rake was the first to describe the loss of ganglion cells in achalasia (221) and

in his original description emphasized that the body of the oesophagus was

affected more than the lower end. The abnormality of those remaining was

noted by Botar and Rubanyi in 1965, who remarked that the plexus appeared to

have been previously present but was involved in a progressive destructive process.

The number of nerve fibres also appears to be decreased but the author from his

experience using a modified Bielschowsky staining technique is not able to say

whether this is a loss of the larger extrinsic nerve fibres or the smaller intrinsic

fibres. Cellular infiltration by small mononuclear cells has been noted

(28, 60, 196, 205, 221). Unpublished work by the author can find no correlation

between cellular infiltration and the severity of the disease and the majority of

autopsy cases do not show this infiltration. It is probably not connected with

epithelial ulceration but it may possibly be related to the dilatation or surgical

procedures which precede death. In some cases this infiltration may also extend

into the surrounding muscle, but not to the submucous layer.

In aganglionic megaduodenum there is an absence or decrease in the number of

ganglion cells and a similar small cell infiltration may also be seen. The tissue

spaces representing the original site of Auerbach's plexus, are still evident but

in this type of agangl ionic bowel there is a marked overgrowth of nerve fibres

in contra-distinction to achalasia (14).

In Hirschsprung's disease ganglion cells are usually completely absent but in

achalasia a total loss is rare. This total loss is confined to the narrow segment

17

and then there is a zone of hypoganglionic bowel of varying length. In this

transitional zone the appearance of the cells suggests a progressive progress

(27, 230, 264). The spaces representing the original site of the plexus are

present but filled with numerous nerve fibres (27, 183, 253). In the rarer cases

where the aganglionic bowel extends to the duodeno-jejunal flexure no such

nervous overgrowth is seen (277). A cellular infiltration has been rarely

observed similar to that found in achalasia (36, 264).

In the extrinsic nerve supply the abnormalities discovered have mostly been in

achalasia and almost no work has been done on similar lesions in Hirschsprung's

disease. Reduced numbers of cells in the dorsal motor nucleus of the vagus have

been found in achalasia (45, 46, 156). A similar lesion of the nucleus ambiguus,

the nucleus for the striated muscle of the oesophagus, was also found in human

achalasia (156). The lesions in the vagal nucleus are specific, bilateral and

only of that part of the dorsal motor nucleus that supplies the smooth muscle of

the oesophagus. In achalasia a lesion of the trunk of the vagus was first suggested

a long time ago (126) but no evidence was obtainable by light microscopy

(87, 175, 176). Recently electronmicroscopy shows a definite decrease in the

numbers of fibres and a progressive destruction of both myelinated and unmyelinated

fibres in the trunk of the vagus, although it is not certain whether they are

efferent or afferent (45).

•':

IS

ABNORMALITIES OF THE MUSCLE

Little attention has been paid to the muscle changes in achalasia. The sphincteric

muscle at the lower end of the oesophagus is usually of normal thickness (278)

although a few cases of hypertrophy have been described. The body of the

oesophagus may be normal, thickened or dilated and thin. It is possible that this

represents an early stage and the latter a terminal decompensated stage of the

disease process.

Rake in his original description noticed that some muscle fibres seemed larger than

usual (221). In the author's experience this usually applies only to the striated

muscle. Sclerosis of the smooth muscle is on the other hand commoner (7f 8,

175, 176, 280, 281). It predominantly affects the circular layer of muscle and the

muscularis mucosa (280) but this distribution is not so clear in those cases the author

studied. No evidence is available as to whether the body of the oesophagus or

the lower end are most affected but the sclerosis appears proportional to the ganglion

cell loss.

Electronmicroscopy has shown definite changes which consist of loss of intercellular

bridges, the nexus, alterations of cytoplasmic condensates, changes in the size and

the shape of the cells and intercellular collagen infiltration (45, 46, 119).

Occasional hypertrophy of individual smooth muscle has also been seen under the

electronmicroscope (119).

•I

19

PREVIOUS AETIOLOGICAL THEORIES

General

Many of the older aetiological theories, more frequent in achalasia than

Hirschsprung's disease, are completely untenable with our present knowledge of

physiology and the extent of the pathological lesions but others deserve careful

consideration. Before the discovery of the ganglion cell loss, weakness of the

oesophageal wall (297), compression of the oesophagus by the aorta (117), the

liver (196) or diaphragm (144) were suggested but these ideas have no physiological

basis.

Purton in 1821 described one of the first cases of achalasia and mentioned that the

patient had received a blow on the sternum thirty years previously (218). Trauma

was also considered important in the aetiology at the beginning of this century (103).

The subject was recently reviewed and thought to be significant (243) but the

majority of patients do not have a history of trauma. Many experienced clinicians

are impressed that achalasia patients are mentally abnormal. Two studies show that

the majority have some psychological abnormalities (184, 234). They were passive,

shy, sensitive and lack aggression. Systematic psychotherapy helped in all twelve

patients treated in one series (234). It is impossible to decide whether these

disturbances are the result or the cause of difficulty in swallowing. No such study

has been done on patients with Hirschsprung's disease who have had their symptoms

relieved by a successful operation. Mickulicz suggested that spasm of the sphincter

was the cause of achalasia (190) but oesophageal motility studies show no spasm but

rather a reduced or normal pressure in the zone of elevated pressure at the lower end

of the oesophagus (59, 85). As early as 1888 a failure of the sphincter to relax on

20

swallowing rather than spasm (82, 188) and an abnormality of the coordinating

mechanisms was postulated (232), but this theory had to mature a long time before

it was proved correct by oesophageal pressure recordings (59),

The discovery of the ganglion cell abnormalities made possible a more logical

approach to the aetiology but although this provided an anatomical basis for the

physiological changes. The cause remained unknown. To postulate that dilatation

itself caused the death of ganglion cells (290) does not help unless the cause of the

dilatation is known and is most unlikely to be true in the absence of experimental

evidence and the knowledge that the dilated bowel in Hirschsprung's disease contains

normal ganglion cells.

Bacterial invasion of Auerbach's plexus was proposed (36). A virus was incriminated

(17, 199), Etzel (88) also suggested Vitamin B| deficiency for the numerous cases

seen in Brasil, based on the clinical association with malnutrition. Experimental

work with vitamin B deficiency in other animals although producing motility disturbances,

has not produced achalasia (54). The main argument against the infectious theories

is that although a virus, such as the poliomyelitis virus, can be specific against a

specific type of nerve cell, they do not explain the anatomical distribution in which

only certain parts of the gut are affected. Oesophagitis as an underlying cause of

the bacterial invasion might explain the cellular infiltration at the lower end of the

oesophagus but does not explain why the body is more affected than the lower end.

There is usually no evidence of reflux in achalasia before treatment nor any colitis

in Hirschsprung's disease.

One infective lesion definitely does cause ganglion cell loss, not confined to

any one part, because Chagas1 disease affects the whole gut. At this stage the present

knowledge of this disease and whether it could be responsible for all cases of aganglionic

bowel will be discussed.

21

||. Chugas1 disease.

Chagas himself first suggested the possible connection between the "megas" and

acute Chagas disease which he first described in 1909 (48, 49). Individuals are

inoculated by the faeces of a reduviid bug, which contain trypanosoma Cruzi

parasites, and suffer from the acute phase of Chagas1 disease with a mortality of

lO^o. After the initial infection repeated inoculations take place and the individual

may or may not enter the chronic phase of the disease. Previous infection can be

recognised by a complement fixation test from which the number of people infected

in Brasil is estimated at about four million and in Venezuela one million (160). The

parasite passes into the lymphatics of the gut which are mainly between the muscular

layers. Reproduction occurs through an intermediate stage in a muscle cell, which

subsequently bursts and liberates parasites into the blood stream. Since Auerbach's

plexus is in this region it is liable to injury and the ganglion cells are killed either

by a neurotoxin (159) or an allergic arteritis (66, 206). The subsequent post-gang I ionic

denervation and muscle damage affects mainly the heart and gut (162) but the urogenital

tract, gall bladder and bile ducts may also dilate. The fact that most patients with

megacolon and megaoesophagus had a positive complement fixation test (66, 67, 69,216)

establishes some correlation and the discovery of leishmania stage in megaoesophagus

was additional circumstantial evidence (163). The experiments producing the chronic

form of the disease in mice (207), dogs (207) and monkeys (113) were proof that the

dilated gut could be caused by trypanosomiasis. The ganglion cell loss in Chagas1

disease affects the whole length of bowel indiscriminately but the colon dilated earlier

and more often than the oesophagus or small bowel. Motility studies of the oesophagus

revealed early changes in asymptomatic patients with proven Chagas1 disease, by

complement fixation test, which were more marked when a concomitant megacolon was

present (215). This work indicates that ganglion cell loss in the oesophagus with or

without dilatation may occur without symptoms. If the colon and oesophagus are

22

equally affected by ganglion cell loss, then the cause of decompensation of the

colon with the production of symptoms must be due to an inherent property of the

large bowel. This may be due to the solidity of its contents or the lack of normal

peristalsis and the absence of the effect of gravity. On this evidence many cases

of non-trypanosomal European achalasia may exist without symptoms.

The parasite itself has a wider distribution than South America and has been described

in the southern states of U.S.A. (31, 121, 124, 183, 279). The reduviid bug which

is the important vector, has also been found in the U.S.A. (286, 288). In one series

of children in an endemic area in U.S.A. Chagas1 disease was diagnosed by

complement fixation test in 2.5% but no permanent defects were noted (287).

Ingelfinger has described four possible cases of Chagas1 disease megaoesophagus in

the indigenous inhabitants of the Southern States, of which one also had E.C.G.

changes (89). This is the total extent of Chagas1 disease in the Southern States of

U.S.A., where both the parasite and the reduviid bug exist. There is no evidence

that Chagas1 disease exists in Europe (161) or Asia (131). Therefore infection by

trypanosomiasis is not the cause of agangi ionic bowel in countries outside South America.

HI. Extrinsic nerve lesions.

Numerous theories have been based on lesions of the extrinsic nerves. Since the

sympathetic system either has no effect on motility or increases the tone in the

musculature, only lesions of the parasympathetic have been postulated. These could

either exist in the vagal nucleus or the trunks of both vagi in achalasia or in the

pelvic parasympathetic in Hirschsprung's disease. No such theory has been postulated

for aganglionic megaduodenum.

23

The experimental evidence for such lesions is extensive and has a long history.

In 1839 Reid in Edinburgh produced dilatation of the oesophagus in rabbits and

dogs after section of the vagus and this was repeated by Claude Bernard in 1849.

Dilatation of the oesophagus can be obtained by lesions of the vagus above the

hilum of the lung, but below this level the effect is confined to the area supplied

below the divided nerve (44). Recently destruction of the vagal nucleus in the

medulla of cats and dogs (128, 238) and bilateral supranodal vagotomy in dogs has

produced a dilatation of the whole oesophagus (127). The results have been confused

by species differences and although permanent dilatation can be obtained in dogs

and rabbits it is only temporary in cats and monkeys. This is almost certainly due

to the return of autonomous peristaltic action in the oesophageal smooth muscle of

cats and monkeys whose distribution is the same as the human, whereas the striated

muscle which extends to the lower end of the oesophagus in dogs and rabbits never

recovers (38, 150). Sympathectomy normally has no effect on motility (107) and

after a preliminary vagotomy the return of normal activity caused by a sympathectomy

(149) must be considered part of the normal recovery of function in denervated smooth

muscle. The experimental evidence for extrinsic denervation in the colon and

rectum is not so extensive. Removal of the pelvic parasympathetic supply may cause

a dilated colon but there is usually retention of urine due to the denervated bladder

and the animals do not survive (3, 142). Although dilatation of the oesophagus may

be produced by bilateral vagal lesions at or above the cervical region, the condition

produced has certain important differences from achalasia. First, autonomous

peristalsis in the smooth muscle of the oesophagus returns after vagotomy. Secondly,

when the extrinsic nerves are destroyed, there is no evidence that the ganglion cells

degenerate. Although one study in monkeys has suggested a reduction in ganglion

24

cells in the oesophagus after vagotomy (24), the majority of evidence shows that

transynaptic degeneration of ganglion cells after pre-gangl ionic denervation does

not occur (129, 147, 150, 172, 185, 205, 229, 242, 253, 272, 276). Most of these

workers have concentrated on morphological changes but a recent study by the author

using a new histochemical technique, by which the ganglion cells in large areas of

oesophageal wall could be counted, showed no decrease in ganglion cells after

subhilar vagotomy in dogs. If an extrinsic nerve lesion does not cause degeneration

of the ganglion cells, the lesions found in the extrinsic nerves must be secondary to

the primary damage of the ganglion cells. Retrograde degeneration in the vagal

nucleus have been described experimentally (19, 97, 292). The probability of such

a wide anatomical distribution of a primary lesion is unlikely because it would be

extremely rare for a pathological process to destroy only a part of the dorsal motor

nucleus of the vagus on both sides of the medulla. But if retrograde degeneration

produces these separated lesions, then the primary pathological process is more likely

to be in the gut wall.

IV. Neural crest lesions.

Neural agenesis has been proposed as a cause of aganglionic bowel (93) and another

group of workers with great experience of Hirschsprung's disease have suggested a

lesion of the neural crest (26). They base the idea on the experimental work in the

chick embryo of Yntema and Hammond, who extirpated the vagal neural crest and

adjacent neural fold within the first few days of development (294, 295) and this

work has been repeated in a turtle (293). Complete removal caused the disappearance

of intrinsic ganglia in the lungs, heart, oesophagus, stomach and intestines and the

incomplete removal produced a decrease distally more than in the proximal parts of

25

the intestine. This idea is attractive because the degree of damage to the neural

crest changes the length of aganglionic bowel to explain the "short" and "long"

segments of Hirschsprung's disease. The lesions produced by neural crest extirpation

are widespread, involving heart and lung gangifa, absence of spinal ganglia at the

level of the lesion and a reduction or absence of sympathetic ganglia as well as the

changes mentioned above. No mention of vesical of ureteric ganglion loss was

made in this work but these would be expected. Such a widespread lesion obviously

does not occur clinically. If a lesion of the neural crest were to explain the loss

it would have to be finely localised to the neural crest of both sides and occur

between the 5th and 10th somite stage in the first week of embryonic life. In

Hirschsprung's disease, the area where Auerbach's plexus should be, are very

noticeably filled with neural fibres rather than cells. In a congenital lesion at

such an early stage one would expect no evidence of these spaces and histological

appearances are more compatible with the cells having been present and then

disappearing, than never having developed. Another objection to this theory is that

it can not explain achalasia, because this is probably an acquired disease to the

extent that ganglion cells are often seen degenerating, and a few may remain and

the distribution in this instance would be expected to involve the whole bowel.

A further criticism is that the "zonal" Hirschsprung's disease and aganglionic

megaduodenum are unlikely distributions of a centrally occurring lesion.

26

SUMMARY OF PREVIOUS AETIOLOGICAL THEORIES

It is valuable to summarise the argument at this point. None of the previously

suggested causes fits all the known facts. The theories of neural crest abnormalities

and extrinsic lesions of the para-sympathetic system are best but there is evidence

that they are not true. A hypothesis is needed that will fit the random distribution

of aganglionic bowel on (I) an epidemiological basis (2) the definite anatomical

distribution in accordance with the arterial blood supply and (3) the associated

lesions in the muscle. Lesions other than those occurring locally in the gut wallS^S

are extremely unlikely, because trans-synaptic degeneration does not occur and

the ganglion cells themselves must be primarily affected. Since the arterial"

distribution is an outstanding feature of the disease one is left with the possible

alternative that an arterial lesion producing ischaemia might be the cause.

EXPERIMENTAL ISCHAEMIA AS A CAUSE OF INTESTINAL ATRESIA

Ischaemia of the gut usually causes other lesions and a digression is necessary to

discuss the effects of ischaemia both in the adult gut and at an early stage of

intra-uterine development. Surgeons are familiar with the result of arterial

obstruction in the gut clinically. The gangrene that develops is either due to an

intra-arterial obstruction due to thrombosis, embolus or compression from the outside

usually by strangulation in a hernia, volvulus or intussusseption. This gangrenous

gut may either be removed surgically or perforate but in certain instances it recovers

spontaneously with ensuing stenosis. Over eighty cases of intestinal stenosis after

a strangulated hernia have been described (50). Experimental work in the dog has

27

elucidated the damage done by ischaemia and the time factors involved (153).

It was shown that epithelium regenerated but that the irreversibly damaged muscle

became stenotic. Experimental gangrene in adult dogs produced peritonitis after

perforation, but if the bowel was sterile peritonitis was unlikely. Experimentally,

dead sterile bowel can be absorbed without trace from the abdominal cavity (170)

but the only time when the bowel is sterile is in utero. Barnard, working with

Professor Wangensteen in Minneapolis, operated on pregnant dogs to produce

gangrenous gut in intra-uterine puppies and when the puppy was born fourteen days

later found a stenosis, web or atresia (12, 13). In these experiments the gangrene

was produced by a volvulus of the small intestine. With the proof of the basic

mechanism provided by this experimental work a classification was postulated for

congenital intestinal small bowel lesions depending on the severity of the

ischaemia (181).

1. stenosis

2. Type I atresia-membrane, septum, web or diaphragm.

3. Type II atresia-proximal and distal blind ends connected by aband-1 ike remnant with or without a V-shaped mesenteric defect.

4. Type III atresia-disconnected blind ends with or without aV-shaped mesenteric defect.

This classification of intestinal lesions is not yet universally accepted although it

has appeared in a textbook (284). Previous theories were based on the concept

that the once solid gut failed to recanalise. Tandler stated that the duodenum was

at one stage of development occluded by epithelium (265) and this was applied

indiscriminatelyito the rest of the gut, supportive evidence being cited that the

oesophagus of the logger-head turtle was also obliterated (148). In man this

probably does not occur (146, 197) although one report describes it (182).

As early as 1901, Bretschneider provided very strong circumstantial evidence that

the theory of "failure to recanalise" was untenable, because he found lanugo,

epithelial cells and meconium distal to the atresia and also demonstrated an atretic

area containing these tissues. This has also been confirmed by others (32, 204, 236).

The occlusion must occur later than the fourth week of intra-uterine life when

meconium is first secreted (284) and the gut must have been patent to allow the

passage of meconium and lanugo.

In 1883 Gartner suggested that atresia and stenosis were due to volvulus because

the lesions were common at the extremities of the bowel and most susceptible to

rotation (95). The finding of rotational defects in a significant number of colonic

atresias is circumstantial evidence for this (94). Bland-Button's principle that

congenital obstruction and narrowing are always found at the situation of embryological

events is applicable here (25). Most of the atresias and stenoses are situated where

the gut is most susceptible to volvulus, intussusseption or strangulation in a hernia.

Duodenal atresia may be caused by the rotational mechanism involved in placing

the duodenum on the right side of posterior abdominal wall, and may also be associated

with malrotation (90, 110). The numerous and often multiple small intestinal atresias

are more likely to be caused by obstruction in an umbilical hernia rather than the

main volvulus defect, although a volvulus affecting only the small bowel could exist.

The localised colonic atresias and possibly some of the small intestinal defects may

be caused by intussusseption. The finding of intussusseption with colonic atresia

29

by Parkulainen is additional evidence (21). It must be emphasized that although

Barnard's work shows that the basic mechanism of ischaemia could be a cause of

intestinal atresia this was only applied in the small intestine. The same mechanisms

for the remainder of the gut have not yet been proved experimentally.

TEMPORARY ISCHAEMIA

In atresia the ischaemia must last longer than a critical period after which most of

the tissues are irreversibly damaged. Little attention has been paid to the duration

of ischaemia or whether the volvulus corrected itself. If the volvulus untwists

itself, atresia may result.without any evidence of the accident having occurred.

Stenosis and the various types of atresia probably result from a long period of

ischaemia, but the bowel could be ischaemic for a shorter time without so much

muscle damage, and it is conceivable that nerve cells could be damaged without

the other tissues being affected. Kessler and Linden found that with experimental

ischaemia of the gut 3 1/2 - 4 hours was the critical period during which the neural

tissue was destroyed irreversibly without damaging connective tissue, muscle or

epithelium (153). The original work on temporary ischaemia of the gut was performed

by Cannon and Burket in 1913 (39). They compressed the small intestine of a cat

between glass plates to render it ischaemic for at least three and a half hours and

selectively destroyed ganglion cells. This compression technique has been

successfully applied to the oesophagus (55, 61, 238). Hukuhara developed this

further by perfusing the small intestine through its arterial supply with a non-

oxygenating substance (136, 137) and Okamoto and his associates with the same

method successfully destroyed ganglion cells in the oesophagus (205). They

shortened the time of anoxia to one hour by adding mercuric chloride to the perfusion

fluid. Their procedure is open to severe criticism because it does not assess the

physiological effects of ischaemia alone, the mercuric chloride adds an unknown

factor and almost certainly produces so much tissue damage that a stricture at

the lower end of the oesophagus is formed, as demonstrated by one of their illustrations.

A recent attempt to produce ischaemia of the oesophagus by a similar method

without mercuric chloride was made in fifteen dogs by the author (80). In these

experiments the lower end of the oesophagus was freed so that the left gastric artery

provided its sole arterial supply. After washing out the blood the area was left

ischaem'c for at least four hours and then the normal anatomy was reconstituted.

Early motility changes in the muscular coordination of the oesophagus were noted

but within nine months they returned to normal and there was no evidence of any

stricture. Morphological ganglion cell changes and a reduction in their number

were found. This series of experiments failed to produce a permanently dilated

oesophagus possibly because only the lower ten centimetres of the oesophagus were

made Sschgemic and the ganglion cell loss was only about 50% of the normal number.

It has been suggested by Koberle with his experience in Chagas1 disease that at

least 90% of the ganglion cells must be absent before incoordination of the

oesophagus leads to dilatation (161, 162). These experiments succeeded in showing

that the basic mechanism of the selective destruction of ganglion cells by temporary

ischaemia was possible. Other recent experiments with anoxia have selectively

destroyed ganglion cells without muscle damage in the small and large intestine

(137, 200, 262, 263) although one attempt has been unsuccessful in the colon of

the dog (73).

This temporary ischaemia is based on the concept that of the four basic tissues

in the intestinal wall-connective tissue, epithelium, muscle and nerve - the latter

is most sensitive to anoxia (75) and no regeneration of any remaining ganglion cells

is possible. Epithelial tissue is most easily damaged but regenerates (35), muscle

31

is also dmaged but shows very little change by light microscopy. No

electronmicroscopic change in smooth muscle or skeletal muscle are available

but evidence in cardiac muscle after ischaemia shows a striking increase in the

amount of intercellular separation (34). The ganglion cells themselves may be

irreversibly damaged and show cytological changes in the early phases after

ischaemia but may possibly take up to six months to disappear (80). Mitoses are

not seen in mature ganglion cells so hyperplasia is presumed not to occur. The

presence of a double nucleolus in the nucleus of a damaged ganglion cell is most

likely the result of the damage and does not indicate regeneration. Although this

evidence suggests that regeneration of neural tissue can not occur, ganglion cells

• can be grown under special conditions in tissue culture and an increase of cells has

been alleged in congenital pyloric stenosis (18), regional enteritis (65), above

stenosing jefunitis (114) and ulcerative colitis (255). If this hyperplasia occurs,

it is at the moment inexplicable and is the only known example of neural cells in

any part of the body undergoing compensatory hyperplasia. In the absence of any

positive evidence to the contrary it must be presumed that once the majority of

the ganglion cells are destroyed there is no regeneration of the remainder.

Experimental destruction of ganglion cells has also been achieved by placing

animals in a hypobaric pressure chamber representing an altitude of 4000 metres

(240) and by the use of carbon dioxide snow which causes vasoconstriction and

anoxia (7, 8). The damage produced by the cold from carbon dioxide snow is

not completely specific and the author thinks that strictures of the lower end of the

oesophagus were probably caused in this work, but the ganglion cells were

successfully destroyed. Sclerosis of the muscle such as seen in some human cases

of achalasia were produced. Alnor was the first to suggest that a localised

disturbance of circulation, producing ischaemia, might be the cause ofeanglion

cell loss (8).

32

There now appears to be sufficient experimental evidence that ischaemia of

approximately four hours duration can produce ganglion cell loss without destroying

other tissues. Obviously if the ischaemia lasts longer than four hours there is a

greater chance that all the ganglion cells will be destroyed, but some muscle

damage may occur (153). As long as the muscle damage is minimal no scarring

and no contraction will occur, but as soon as it is severe enough stenosis will

result. As atresia is probably caused by intra-uterine accidents of volvulus,

intussusseption or strangulation, it seems logical that aganglionic bowel could

occur in the same way. A review of the present knowledge of the embryology

is essential as the next step in this discussion so that the stage of development of

the gut in relation to intra-uterine vascular accidents is accurately known.

EARLY EMBRYOLOGICAL DEVELOPMENT OF THE GUT

The following paragraphs contain a discussion on the development of the individual

components of the intestinal wall, the development of the oesophagus and the

rotation that the gut undergoes in utero before it assumes its final adult configuration,

Smooth muscle layers in the intestine are present by 33-35 days (154). In striated

muscle, development can occur without innervation (2) and there is also evidence

that this can occur in smooth muscle (272). In humans the growth of smooth muscle

has not been as well studied as skeletal muscle but since the upper end of the

oesophagus contains skeletal muscle this may be pertinent. At seven weeks the

first individual skeletal muscle is differentiated, at ten weeks small identifiable

cells are recognised, by sixteen weeks there is no more splitting and striations

33

are present. In the second half of intra-uterine life there is an increase in the

size but not the number of muscle cells. Somatic nerves are seen in the connective

tissue at 10 weeks and make contact with the muscle at eleven weeks, with the

subsequent development of motor nerve endings at 12-24 weeks. Muscle spindles

are seen by eleven weeks and all essential elements are present by fourteen weeks.

By twelve weeks there is sufficient anatomical organisation for the earliest human

embryo reflexes to be present.

There is not so much evidence about neural tissue in the human as in the chick,

but the vagus is well formed by 30 days (256) and the myenteric plexus by the

38th day (154). The ganglion cells are in fact present at an earlier stage and

myelinated fibres have been reported in the intermuscular plexus by the 18th day

(249), but at this stage are usually only represented by Dogiel Type I (165).

In the chick embryo details about the development of neural innervation are

available In great detail but obviously the time factors cannot be indiscriminately

applied to humans. At 86 hours in the chick the visceral branch of the vagus is

present and by 125 hours the vagus reaches the pylorus where it stops ; by the 4th day

the sympathetic also has visceral fibres (272). If the extrinsic nerves are normal

the ganglion cells develop pari passu with the growth of the parasympathetic

from both ends (40, 272). If the vagus is divided in the chick before the ganglion

cells are seen the cells of Auerbach's plexus still develop (40, 68, 272).

|n spite of much work on whether the ganglion cells of Auerbach's plexus arise

from mesoblasts (272) parasympathetic neuroblasts (202, 294) or sympathetic

neuroblasts, the probability is that they arise from the parasympathetic nervous system.

34

Blood vessels are found entering the human embryo intestinal wall by the 37th

day (153) and definite adult type blood vessels develop later.

The development of the intestinal epithelium is controversial. In the oesophagus

the majority of the opinion is that the lumen is never occluded (146, 154) although

in the logger-head turtle an epithelial plug was found (148). The duodenum seems

more likely to be obstructed by a relative overgrowth of epithelium (265). The

rectum and colon are very rarely affected by this process in the human (182).

The development of the thorax and the descent of the diaphragm is important in

relation to the oesophagus. On the 33rd day the diaphragm is attached to the

caudal end of the infrahyoid mass and by the 34th day it is disconnected and

descending (154). This descent is caused by differential growth in which the

oesophagus markedly elongates. There is disagreement as to when the diaphragm

has fully descended. Keibel and Mall say at 36 days, but it may be later.

Between the 5th and IOth week the gut enlarges in length to such an extent that

there is not room in the abdominal cavity and it prolapses through a large umbilical

hernia. At the 5th week there is only a single loop but with the vast increase of

length the loops become more complex. Towards the 10th week the gut begins to

return, undergoing a 270 degree anti-clockwise rotation, so that the duodenum

reenters the abdomen first and the caecum abruptly and finally at the 10th week

(10, 77, 116). This anti-clockwise rotation is still evident in the adult by the

position of the bowel, the taeniae coli of the colon, the anti-clockwise spiralling

of the longitudinal muscle of the small intestine (42) and the oesophagus (252) and

the rotation of the vagi on the oesophageal wall.

35

A volvulus is most likely to occur when the gut is prolapsed through the umbilical

hernia between the 5th and 10th week of intra-uterine development. Since the

rotational effects of the gut are more evident towards the end of this period the

chances of volvulus occurring then are greater than in the 5th to 7th week.

It is probable that a volvulus results from excessive rotation between the 7th and

10th week. By the 7th week the intestinal wall has most of its essential components.

The smooth muscle cells are present but still dividing. Auerbach's plexus and

the extrinsic nerve supply are in situ. If four hours of ischaemia occurred at

this stage the nerve cells would be destroyed and any muscle damage would be

compensated by hyperplasia of the remainder, because this process normally

persists until the 16th week.

EMBRYOLOGY OF OESOPHAGEAL ATRESIA AND TRACHEO-OESOPHAGEAL FISTULA

The pathology of these early embryonic events has been described in an excellent

contribution on tracheo-oesophageal fistula by Smith (247). This study and that

of Streeter (256) are based on a survey of over a hundred human embryos in the

Carnegie Institute. Smith studied three of the five available early embryos with

oesophageal atresia ( 100, 112, 177, 196, 291). It was concluded that the lesion

occurred at the critical stage when the trachea and oesophagus are separating

before the fifth week of intra-urerine development (256) and emphasized that the

separation was caused by endothelial proliferation on the inside of the common

tracheo-oesophageal tube as with the endocardial cushions, rather than a

constriction from the outside. Tracheo-oesophageal fistula was compared with

urogenital fistula and it was mentioned that atresia of the ventral and secondary

developing system was rare. Lesions of Type I or II in the oesophagus may arise

from a failure of the fistula to persist or develop. Smith found no support for

the epithelial occlusion theory but suggested an abnormality of differential growth

r

36

and insufficient tissue availability. The value of this work lies in localising

the formation of a tracheo-oesophageal fistula to some time before the 33rd day.

Since the trachea and the oesophagus are separated after the 33rd day it would

be unlikely that a developmental error would cause a fistula after this. It is

suggested that those atresias of the oesophagus which are not associated with

fistula must be caused by a developmental error occurring after the fifth week

when the trachea and the oesophagus have already separated.

TRANSITIONAL AGANGLIONIC ZONE BETWEEN ATRETICAND NORMAL BOWEL

Further circumstantial evidence for the connection between atresia and

aganglionic bowel would be provided if they were both described in the same

patient. Indeed if the same aetiology is postulated there should be a zone of

transition between atresia and aganglionic bowel as well as the transition between

aganglionic and normal gut. Parkulainen and his associates have described the

transition of recta! atresia through aganglionic bowel to normal in 15 cases of

rectal atresia (211). This does not occur in every case but is more likely to occur

in Type III. The transitional zone has been reported by others (29, 214, 230)

but denied by Swenson (257), although one case was discovered in a series of

150. From the records of 32 paediatric centres it has been calculated that this

transition occurs in 3.4% of rectal atresia (155). But this percentage increases,

QS Parkulainen demonstrated, if Type III atresias alone are considered (211).

In the oesophagus there is physiological evidence of disturbed motility after the

repair of a tracheo-oesophageal fistula (72, 84, 115, 178, 246). This may be

the effect of the operation but deficient peristalsis has been noted in the distal

blind pouch before the operation (52, 157). This abnormal and deficient

37

peristalsis could be caused by a deficiency of ganglion cells in the body of the

oesophagus. The author studied the material available at the Mayo Clinic

representing unoperated tracheo-oesophageal fistulas and found definite evidence

of reduced ganglion cells in a few cases. This was rare/ and if found, occurred

usually in the distal segment and only for a few mm. It was quite often associated

with muscle damage but no correlation to the type of tracheo-oesophageal fistula

was possible. The explanation of why the lower end of oesophagus and not the

upper end is involved by this loss may be due to the poorer blood supply of the

lower end (18). No striated muscle was found in these cases in the distal segment,

so if an extrinsic nerve lesion were to have been caused during the repair, the

smooth muscle would be expected to resume autonomous control. In some cases

the gastro-oesophageal junction possibly contained reduced numbers of ganglion

cells but no definite conclusion can be drawn with the limitations of the present

technique and in the absence of further studies.

The hypoganglionic segment in Hirschsprung's disease shows a great variation in

length so the aganglionic transitional segment may be expected to show some

variation. There is enough objective evidence that agangl ionic and atretic

bowel can occur in the same patient with a transitional zone. This is not found

in every case and the reason for this is not obvious.

EPIDEMIOLOGY OF ATRESIA AND STENOSIS

It has been emphasized earlier that the anatomical distribution of aganglionic

bowel had certain similarities to that of stenosis and atresia. If the same mechanism

is postulated for these lesions, the incidence of the different types might help in

38»

elucidating some of the aetiological factors. Few epidemiological studies

are available to give a true incidence so the figures from hospital series must

be analysed. Such numbers are more reliable when the majority of the affected

patients are treated in any one centre. American and London figures are

suspect because many children are treated privately or in other hospitals.

Provincial centres such as Liverpool, where a neonatal unit treats almost all the

patients, provide the best available comparative figures (92, 277). Forshall

points out that since 75% of the children in Liverpool and the surroundings are

born in hospital there are relatively few patients lost because of failed diagnosis (92),

Oesophagus.

One epidemiological study assesses that oesophageal atresia in New England

occurs at the rate of I : 5000 or more live births (140). A calculation from the

available Liverpool figures gives a rate of : 4000 (92, 227). The figure of

I ; 800 pregnancies from Bristol is almost certainly biased by selection and is

too high (20). Oesophageal and rectal atresia each account for 30% or more

of the total number of atresias, which means that they are the most common

(92, 94), although the Great Ormond Street Hospital for Sick Children figures

suggest that oesophageal atresia is not so common as rectal atresia (56, 57). The

usual classification of tracheo-oesophageal fistula with oesophageal atresia is

that of Vogt (275) and his original figures, in which 8% are Type III and the

minority have atresia alone, are still basically true. It seems logical to add the

rarer tracheo-oesophageal fistula without atresia to the classification and the

latest figures from Great Ormond Street indicate this group form 5% of the

total (56). In 1966 only 70 of these had been described in children (195) but

they are frequently not diagnosed. The so-called traction divert!culum of the

mid-oesophagus with a fistula, once attributed to the traction of tuberculous glands

39

but whose incidence has not decreased with the reduction in tuberculosis, is

now considered congenital and would be the persistent equivalent of a fistula

without atresia (298). If the adult diverticula are considered to be congenital

then the incidence of tracheo-oesophageal fistula without atresia is probably 5%I m

of the total fistulas with or without fistula. Congenital stenosis of non-peptic

origin has been described in children and adults (106, 115, 244). They usually

consist of incomplete obstruction in the middle one-third or two-thirds extending

2-3 mm. or rarely longer. Girdany has described more than thirty such cases

From Pittsburgh in a ten-year period (99). These figures result from careful work

so the condition must be considerably under-diagnosed. Congenital webs are even

rarer (193) although Guisez was reported having found 5 in 2000 oesophagoscopies

(266). Webs and stenoses have been described together (106, 118, 135) and a

web with achalasia once (235). The prevalence of achalasia is I : 10,000

in the one epiderniologica! study available and the incidence is probably

I • 100,000 (.79).

From these figures it will be seen that atresia of the oesophagus with a fistula

occurs at about I : 5000 live births.

Atresia alone is ten times as rare at I : 50,000. The figures for congenital

stenosis are misleading because the condition is under-diagnosed. Achalasia

is even rare and occurs at about I : 100,000.

Rectum.

Rectal atresia is usually subdivided accordingly to the classification of Ladd (168)

but it has been pointed out that Type IV is colonic atresia and not rectal (94,236)

40r

although this is not universally accepted. No epidemiological study is

available for this condition but it has the same incidence as oesophageal atresia,

occurring at least in I : 5000 births (92, 94, 227). Most of the Type III, which

form the majority, but almost none of Type IV are associated with fistulas.

Stenosis of the rectum is rare, and it is difficult to assess the true incidence from

the literature. The classification of stenoses in the ano-rectal region is not as

simple as in the oesophagus. If Typ« IV is considered colonic then the figures

for colonic atresia and stenosis can be compared. Lesions of the colon are

fifty times rarer than those of the rectum (94) and the colon is more commonly

affected distally than proximally. In the same series there were two zonal

stenoses and three zonal afresias of the colon. Hirschsprung's disease occurs

at about I : 10,000 and the distal colon is far more frequently affected than the

proximal, with zonal aganglionisis at 1-2%.

From these figures no clear pattern arises. But rectal atresia is commoner than

Hirschsprung's disease. Stenotic and atretic lesions similar to the anatomical

distribution of Hirschsprung's disease occur with approximately the same proportional

incidence.

Duodenum.

Duodenal atresia is about half as common as oesophageal or rectal atresia (94)

and occurs in about I : 12,000 live births (92, 227), \5% have other lesions

distally (90). Stenosis is more than twice as rare. More than half are above

the duodenal papilla and the remainder are below (64, 251, 282). Aganglionic

megaduodenum and the distribution is unknown. Atresia is the commonest lesion.

Stenosis is rare and aganglionic megaduodenum is very uncommon.

41

Jejunum and ileum.

Atresia of the jejunum has about the same incidence as duodenal atresia (94).

Stenosis constitutes about one half of all atresias and stenoses in the small

intestine (III). Rarely stenosis may occur in the adult as a late result of

strangulated hernia but only about 80 have been described (50).

Both congenital atresia and stenosis may be multiple. Aganglionic jejunum

and ileum have only been described in Chagas1 disease. In this disease

aganglionic small bowel may exist without symptoms, so it could exist in counteies

outside South America without recognition. Stenosis must be of a small diameter

before symptoms occur, so many may not be diagnosed.

Once again atresia is commoner than stenosis. In the jejunum and ileum the

lesions are multiple and no aganglionic segment has been described.

Stomach.

To complete the spectrum 52 stenoses, webs and atresias have been described in

the stomach (96) and more webs have been recently added (231). Aganglionic

stomach exists in Chagas1 disease and in the fundus of patients with achalasia.

Stenosis, web and atresia are usually in the middle or the antrum of the stomach.

42

DISCUSSION OF EPIDEMIOLOGY

The distribution of stenosis, atresia and aganglionic bowel have all been

considered together because ischaemia may cause all these lesions. The

overall pattern emerges that atresias are more common than stenosis or aganglionic

bowel. If ischaemia, caused by a volvulus, causes all these lesions, there would

be more chance of permanent than temporary damage, which would affect only

the neural elements. Atresia would then be commoner than stenosis or

dganglionosis caused by lesser degress of ischaemia.

Atresia with a fistula must occur earlier in embryonic development than

atresia alone because the structures concerned have separated completely. The

critical stage is approximately in the 4th to 5th week. Although the gut can

be subjected to rotational stresses before separation has occurred, it is more

likely to occur later between the 5th and 10th weeks when the hernia is larger

and the gut undergoes rotation in its return to the abdomen. The mechanism

for the failure of separation in the development of a fistula with atresia at botfi

ends of the gut is unknown, but it could also be associated with a disturbance of

the blood supply. The effects of the volvulus are not due to the mechanical

compression of the gut itself but to the obstruction of the blood supply. When

the left gastric artery and the superior haemorrhoidal artery are obstructed, the

gut situated at the distal end of the distribution of these arteries is most likely

to be ischaemic. The presence of the descending diaphragm does not alter the

effect of obstructed blood supply and is almost complete before the rotational

stresses occur. When the gut is returning to the abdomen the secondary

43

rotation of the duodenum may cause ischaemia, but this is naturally rarer.

The multiple jejuna I and ileal lesions are more likely to occur later when the

majority of the gut has returned to the abdomen and a small umbilical hernia,

in which gut can strangulate, remains. The zonal lesions of the colon are

probably caused by intussusseption and are therefore extremely rare.

The epidemiology of these lesions offers almost no help in the search for other

causes. Although numerous familial incidences have been reported, overall

epidemiological studies comment on the relatively low position of congenital

malformations in the list of diseases with familial tendencies (158, 203). A

familial tendency to malrotation may be feasible, but the cause of this tendency

is still unknown. Allowing for the variations in diagnosis there seems to be no

change of the disease incidence in recent years, which would exclude any

environmental factors such as infection or irradiation. This comparison suggests

that more aganglionic megaduodenum and congenital stenosis of oesophagus should

be diagnosed than at present.

MUSCLE AND GANGLION CELL CHANGES IN SCLERODERMA.

Aganglionic bowel occurs randomly as achalasia or Hirschsprung's disease or with

a definite cause apparent such as Chagas1 disease where destruction of the ganglion

cell is caused by the Trypanosoma Cruzi. The only other disease known at the

moment where ganglion cell damage occurs is scleroderma, which is a generalised

disease of unknown origin. The smooth muscle of the small arteries is most

affected and a Raynaud's phenomenon may exist. Although the most obvious

44

changes occur in the skin, the oesophagus is abnormal (58). Peristalsis is

poor and there is a reduced zone of elevated pressure at the lower end of the

oesophagus. A reexamination of the two cases reported from the Mayo Clinic

(269) by the author showed in one advanced case loss of ganglion cells of the

oesophagus and stomach, and in the other a reduction in the number as well as

the marked muscular damage. This was first described in South Africa by

Goetz (101). Although the neural tissue loss may be secondary to the muscular

damage, it is suggested that the muscular changes and the ganglion cell loss

are secondary to damage of the small arteries and subsequent ischaemia. In

myotonic dystrophy and progressive muscular atrophy, there is patchy necrosis

of the muscles but the ganglion cells are normal or enlarged (217). The motor

abnormalities of the oesophagus in these diseases are due to muscle damage alone.

ARTERIAL LESIONS

Arterial anomalies were noted in some of the embryos examined by Smith with

oesophageal atresia and tracheo-oesophageal fistula (247) and it has been said

that I O^o have vascular anomalies (115). Whether these abnormal blood vessels

affect the blood supply of the oesophagus or not is unknown, but there is a

definite relationship. Damage to the small arteries in achalasia have been

previously noted (36, 175, 196) but damage to the larger arteries such as the

coeliac axis or the left gastric artery may also occur. Coeliac axis compression

has been diagnosed during life in 17 cases (225) and coeliac angina in 15 further

patients (78). In 110 autopsies 44^4 had a narrowed coeliac axis (71). The

older patients with achalasia may have generalised arteriosclerosis or specific

I

45

damage to the blood vessels for the nutrition of the oesophagus. Abnormalities

of oesophageal motility in nonagenarians (248) and reduction in ganglion cells

with increasing old age has been found (160, 175). Although arteriosclerosis

and old age may be concomitant, the connection between arteriosclerosis and

ganglion cell loss is mere supposition at the moment. In one case, who died after

a Heller's operation, a careful study by the author of the coeliac axis and the blood

vessel supply to the oesophagus revealed no abnormality, but the patient was

relatively young. Each main arterial axis of the abdominal aorta and its smaller

branches has its own specific syndrome and it is tempting, but possibly facile, to

suggest that the left gastric artery lesions produce achalasia.

HYPOCHLORHYDRIA OF THE STOMACH INACHAIASIA

There is a definite increased evidence of hypochlorhydria in achalasia (141),

which is a true finding not due to the failure to the stomach tube to pass through

the lower end of the oesophagus. A possible explanation is that this is also a

lesion of the extrinsic vagal nerve supply but it is probably due to aganglionic

stomach that is unable to respond to any nervous stimulation. In Chagas1 disease

aganglionic stomach has been found and hypochlorhydria has been noted in

20% (274) to 70% (86). When the stomach is hypersensitive to mecholyl,

denoting vagal denervation, there is hypochlorhydria in 100% (274). The

connection of this hypochlorhydria with aganglionic stomach, unassociated with

Chagas' disease, has yet to be proved, but it is unlikely to be due to a vagal

lesion because pyloric obstruction does not occur.

46

SUMMARY

It is considered justifiable to assess all aganglionic bowel together so that common

factors, important in aetiology, might emerge. The physiological differences in

the gut explain why the dilated segment of Hirschsprung's disease contains ganglion

cells and the dilated body of the oesophagus has no ganglion cells. A study of

the epidemiology of aganglionic gut reveals that the diseases affect other species,

most races and both sexes with a relatively random distribution, occurring with a

fixed incidence in populations but no definite aetiological factors emerge.

The anatomical distribution of achalasia of the oesophagus, aganglionic

megaduodenum and the various types of Hirschsprung's disease is analysed and

found to be distributed according to its arterial blood supply.

The associated muscular damage, lesions of the vagus and its nuclei are discussed.

It is deduced that the primary lesion must occur in the gut and that the other changes

are secondary. The experimental evidence for the selective destruction of

ganglion cells by four hours of ischaemia is cited and it is suggested that the areas

of aganglionic gut could have their blood supply interrupted for this length of

time. Between the 5th and 10th week of'intra-uterine life the gut undergoes

rotation through 270° before it returns to the abdominal cavity. Temporary

ischaemia at this stage would make either end of the gut ischaemic. Hirschsprung's

disease and the rare infantile achalasia would ensue and the same rotational

effect could affect the duodenum. The various length of bowel affected and the

numbers of ganglion cells lost are proportional to the type and severity of the

ischaemia. Decompensation of such a congenital lesion, if only a proportion of

the cells were destroyed, might occur 20 to 30 years later to explain some of the

cases of achalasia. If the oesophagus and the rectum were equally affected by

47

ganglion cell loss the rectum would decompensate first and dilate, because of

physiological differences partially associated with the solidity of the contents.

But evidence indicates that many cases of achalasia may be caused by ischaemia

occurring later in life when the blood supply is reduced by arterial obstruction

from thrombosis or arteriosclerosis.i'I

The experimental work of Barnard showed that ischaemia from an intra-uterine

volvulus could cause intestinal atresia or stenosis. A common mechanism would

explain the similarity of the anatomical and epidemiological distribution of atresia,

stenosis and aganglionic bowel.

Oesophageal atresia associated with tracheo-oesophageal fistula occurs before

the 5th week of intra-uterine life before the trachea and oesophagus are completely

separated and the associated fistulas of the rectum probably occur at the same time.

It is feasible but less likely that lesions with associated fistulas are associated with

ischaemia and malrotation of the gut. Atresias without associated fistulas must

occur later than the 5th week when the gut is separated from the surrounding

structures.

48

The hypothesis is that temporary ischaemia for approximately four hours can

selectively destroy the ganglion cells of the gut without damaging the other tissues

permanently and cause an aganglionic segment. This may occur in the adult to

explain achalasia when the arterial supply is obstructed by thrombosis or

arteriosclerosis or as a congenital intra-uterine lesion to explain Hirschsprung's

disease. Many cases of achalasia may represent a decompensated intra-uterine

lesion. Depending on the duration of ischaemia, one of five lesions may result ;

1. Aganglionic bowel

2. Stenosis5

3. Type I atresia - septum, web or diaphragm

4. Type II atresia - band-1 ike remnant

5. Type III atresia - disconnected blind end

49

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