abdominal wall and umbilical cord anomalies

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ABDOMINAL WALL AND UMBILICAL CORD ANOMALIES

Julian N. Robinson, MD, and Alfred Z. Abuhamad, MD

The embryology of the anterior abdominal wall and umbilical cord is presented at the start of t h s article. A chronologic explanation of the abnormal embryology and resulting anomalies is presented in tabular form. This method of presentation demonstrates the effect of the timing of abnormal development on the pathophysiology and severity of the lesion. Techniques involved in the prenatal diagnosis of these abnormalities are described at the beginning of the article. Each of the developmental anomalies of the abdominal wall is then reviewed, again in chronologic order of embryologic development. Anomalies of the umbilical cord are reviewed at the end of the article.

EMBRYOLOGY OF THE UMBILICAL CORD AND ABDOMINAL WALL

. The embryogenesis of the anterior abdominal wall and the umbilical cord commences at the end of the third week, at the stage of the trilaminar germ disc (consisting of endoderm, mesoderm, and ectoderm). This disc is sandwiched between the amniotic cavity and the yolk sac (with the endoderm most proximal to the yolk sac). The ectoderm layer is proximal to the amniotic cavity and in continuum with the amnion. As the embryo grows and curls, this ectoderm- amnion border localizes as the primitive umbilical ring on the ventral surface of the embryo. It is this folding of the disc around the diminishing yolk sac that ultimately results in the formation of the anterior abdominal wall and umbilical cord. Some of the yolk sac is incorporated into the embryo as the midgut (endoderm) and the abdominal wall is formed from the mesoderm (musculature) and ectoderm (skin).

Folding occurs from all sides: cranial, caudal, and lateral. The resulting

From the Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Columbia Presbyterian Medical Center, New York, New York (JNR); and the Depart- ments of Radiology and Obstetrics and Gynecology, Eastern Virginia Medical School, Norfolk, Virginia ( M A )

CLINICS IN PERINATOLOGY

VOLUME 27 NUMBER 4 * DECEMBER 2000 947

948 ROBINSON & ABUHAMAD

umbilical ring contains the allantois; umbilical vessels; extraembryonic coelom; the vitelline duct (yolk sac stalk), and the associated vitelline vessels. As the amniotic cavity rapidly enlarges, the contents of this ring are compressed and elongated to form the umbilical cord. Distally, the cord contains the yolk sac stalk and umbilical vessels; proximally, it contains these and the remnant of the allantois and some loops of bowel. By the 12th week, the amniotic cavity has expanded to such a degree that it comes in contact and fuses with the chorion. The chorionic cavity is obliterated and the yolk sac shrinks and disappears. During the development of the abdominal cavity, there are different rates of development of the enclosed organs and the cavity itself. When more space is required by the abdominal contents, intestinal loops herniate into the extraembryonic coelomic space in the umbilical cord. By the end of the 12th week, however, this space has been obliterated. Similarly the allantois, vitelline duct, and accompanying vessels are obliterated, after which the umbilical vein (usually the left) and two umbilical arteries covered by amnion remain as the umbilical cord. Structural anomalies that result from abnormal embryogenesis and the mechanisms of the primary anomalies of the anterior abdominal wall are demonstrated in Table 1. It can be seen that, in general, the earlier the embryologic abnormality, the more complex the structural anomaly.

ALPHA-FETOPROTEIN AND DEFECTS OF THE ANTERIOR ABDOMINAL WALL AND UMBILICAL CORD

Bergstrand and CzarI5 reported alpha-fetoprotein (AFP) as a fetal-specific protein in 1956. AFP is a glycoprotein, synthesized by the yolk sac, fetal gastrointestinal tract, and liver. It is similar in structure to albumin; however, its exact function in fetal physiology remains to be determined. Under normal conditions AFP is excreted renally and can be detected in the amniotic AFP passes from the amniotic fluid to the maternal circulation by passive means, and can be detected in the maternal circulation, although at very much lower levels. AFP can be detected in the maternal serum as early as 7 weeks of gestation, but does not reach a peak until 28 to 32 Any defect in the fetal integument, excretion system, or placenta and membranes may lead to higher levels in the maternal serum. Increased levels of maternal serum AFP (MSAFP) may be used to screen for defects in the fetal anterior abdominal wall (and many other anomalies). Such screening is performed optimally at the 16th week of gestation. It has been reported that MSAFP is elevated in 89% of fetuses with omphalocele and in 100% with gastros~hisis.9~ If a defect in the fetal anterior abdominal wall is suspected, an elevated MSAFP can be investigated with ultrasound examination of the fetus. It has been reported that in 40 (91%) of 4.4 of fetuses with an anterior wall defect, the lesion could be detected successfully antenatally with ultrasound: and in another series of 21 cases of omphalocele, 18 were correctly diagnosed with ul t ra~ound.~~

ULTRASOUND EXAMINATION AND DEFECTS OF THE ANTERIOR ABDOMINAL WALL AND UMBILICAL CORD

The fetal anterior abdominal wall and umbilical cord should be visualized on routine anatomy survey. Ideally, the fetal anterior abdominal wall should be inspected along the entirety of its length in the transverse plane. In addition, a sagittal view should be obtained. A normal profile and intact integument should

ABDOMINAL WALL AND UMBILICAL CORD ANOMALIES 949

be noted in both of these planes. The abdominal insertion of the umbilical cord should be documented (and recorded) in the transverse plane. The bladder should be visualized and the presence and normal spatial relationships of the other intra-abdominal organs should be noted. For completeness, the genitalia should be examined and the spatial relationship of the lower extremities to the fetal abdomen should be noted. The placental insertion of the umbilical cord should be inspected and the number of cord vessels should be documented. The normal helical appearance of the umbilical cord should be noted. Doppler interrogation of the umbilical cord should be considered and carried out if indicated. Many sonographers routinely use color Doppler to document the number of cord vessels (by visualizing the arteries on either side of the fetal bladder). Pulse Doppler can be used to assess placental impedance by interrogating the umbilical artery and to assess cardiac compliance (in severe fetal compromise) by interrogating the umbilical vein.

GENETIC TESTING AND DEFECTS OF THE ANTERIOR ABDOMINAL WALL AND UMBILICAL CORD

There can be associated chromosomal abnormalities with certain anomalies of the anterior abdominal wall and umbilical cord. The overall risk of an associated chromosomal abnormality with an anterior abdominal wall defect is 24.1%.%, 55, 99, 114 There are many different rates quoted for associated chromosomal abnormality with these anomalies in the medical literature. The incidence varies according to gestational age at the time of diagnosis. The incidence decreases with advancing gestational age because of spontaneous fetal loss or medical intervention. The anterior abdominal wall defect with the strongest association with aneuploidy is omphalocele. The incidence of an associated aneuploidy is 8% for an isolated omphalocoele and can be as high as 46% if there are associated abnormalitie~.~~ Of possible associated aneuploidies, trisomy 18 is the cornmone~t.5~

If an anterior abdominal wall or umbilical cord defect is diagnosed, the parents should receive appropriate genetic counseling and be offered genetic testing (either chorionic villous sampling or amniocentesis). It should be noted that although certain types of anterior wall defects may not be associated with an aneuploidy, the parents may still desire genetic testing because although their risk of aneuploidy is no greater than background risk, an abnormal finding may affect their decision to continue with the pregnancy.

ANOMALIES OF THE ANTERIOR ABDOMINAL WALL

The structural anomalies of the anterior abdominal wall are addressed in the chronologic order of abnormality of embryologic development (Table 2).

Body Stalk Anomaly

Background

Body stalk anomaly (Fig. l), also known as limb body wall complex, congenital absence of the umbilical cord, short umbilical cord syndrome, or cyllosmas, is a very rare abnormality (1 in 14,000 at birth).lz There is some difference in opinion in

Tabl

e 1.

EM

BR

YO

LOG

Y O

F A

NO

MA

LIE

S O

F TH

E A

NTE

RIO

R A

BD

OM

INA

L W

ALL

Ges

tatio

nal

4-6

wk

Age

N

orm

al E

mbr

yoge

nesi

s E

mbr

yolo

gic

Def

ects

R

esul

ting

Ano

mal

y

Bod

y st

alk

anom

aly

In b

ody

stal

k an

omal

y th

ere

are

ofte

n m

any

asso

ciat

ed d

efec

ts a

part

fro

m th

e op

en a

nter

ior

abdo

min

al w

all

(hea

d, s

pine

, and

ext

rem

ities

can

be

invo

lved

). It

is th

ough

t tha

t the

re m

ay

be a

vas

cula

r ins

ult t

hat r

esul

ts in

isch

emia

and

hem

orrh

agic

nec

rosi

s. T

his

may

aff

ect m

any

tissu

es a

nd, i

n pa

rtic

ular

, the

ant

erio

r abd

omin

al w

all.’3

7

shor

t or

abse

nt u

mbi

lical

cor

d,

open

ant

erio

r abd

omin

al

wal

l, of

ten

with

oth

er

abno

rmal

ities

6-7

wk

The

um

bilic

al v

eins

sup

ply

the

ante

rior

ab

dom

inal

wal

l unt

il re

plac

ed b

y th

e om

phal

omes

ente

ric a

rter

ies

(bra

nche

s of

the

aort

a). I

n th

e 7t

h w

eek,

the

righ

t um

bilic

al v

ein

atro

phie

s as

doe

s th

e le

ft om

phal

omes

ente

ric a

rter

y. T

his

leav

es th

e le

ft u

mbi

lical

vei

n an

d th

e ri

ght

omph

alom

esen

teri

c art

ery

to s

uppl

y th

e an

teri

or a

bdom

inal

wal

l.

1. P

rem

atur

e at

roph

y or

per

sist

ence

of t

he

righ

t um

bilic

al v

ein

coul

d in

terf

ere

with

th

e de

velo

pmen

t of

aort

ic c

olla

tera

ls an

d ca

use

righ

t par

aum

bilic

al is

chem

ia.%

2.

Vas

cula

r acc

iden

t of

righ

t om

phal

omes

ente

ric a

rter

y le

ads

to r

ight

pa

raum

bilic

al i~

chem

ia.6

~

Gas

tros

chis

is

righ

t par

aum

bilic

al d

efec

t of

ante

rior

abd

omin

al w

all

7-8

wk

Fold

ing

is c

ompl

eted

with

the

fusi

on o

f th

e m

esod

erm

al m

yoto

mes

in th

e m

idlin

e. T

he

diap

hrag

m i

s fo

rmed

fro

m th

e se

ptum

tr

ansv

ersu

m (

a m

esod

erm

al p

late

bet

wee

n th

e th

orac

ic c

avity

and

the

yol

k sa

c), a

nd

the

vent

rom

edia

l m

igra

tion

of up

per

abdo

min

al m

esod

erm

al f

olds

. The

pl

euro

peri

card

ial

mem

bran

e se

para

tes

the

peri

card

ial

and

pleu

ral c

aviti

es a

nd f

orm

s th

e fi

brou

s pe

rica

rdiu

m.

mes

oder

mal

rid

ge th

at a

rise

s be

twee

n th

e al

lant

ois

and

the

hind

gut.

It se

para

tes

the

cloa

ca in

to th

e ur

ogen

ital s

inus

and

the

anor

ecta

l can

al.

The

uror

ecta

l sep

tum

is a

tran

sver

se

The

ante

rior

wal

l of

the

blad

der

and

over

lyin

g ab

dom

inal

wal

l is

form

ed b

y th

e m

esod

erm

al m

yoto

mes

mig

ratin

g ar

ound

th

e cl

oaca

l mem

bran

e an

d fu

sing

in th

e m

idlin

e.

Fold

ing

is c

ompl

eted

with

the

fus

ion

of th

e m

esod

erm

al m

yoto

mes

in th

e m

idlin

e. T

he

abdo

min

al c

avity

com

mun

icat

es w

ith t

he

umbi

lical

cor

d w

ith p

ossi

ble

phys

iolo

gic

hern

iatio

n of

the

inte

stin

es u

ntil

clos

ure

of

the

exoc

elom

ic sp

ace

at 1

2 w

k.

7-12

w

k

Def

ectiv

e fu

sion

of

the

mes

oder

mal

m

yoto

mes

in th

e m

idlin

e, la

ck o

f fo

rmat

ion

of t

he s

eptu

m tr

ansv

ersu

m,

faile

d m

igra

tion

of th

e up

per

abdo

min

al

mes

oder

mal

fol

ds, a

nd f

ailu

re o

f fo

rmat

ion

of th

e fi

brou

s pe

rica

rdiu

m.

Failu

re o

f de

velo

pmen

t of

cloa

cal m

embr

ane

and

failu

re o

f fo

rmat

ion

of t

he u

rore

ctal

se

ptum

and

def

ectiv

e fu

sion

of

the

mes

oder

mal

myo

tom

es in

the

mid

line.

Failu

re o

f de

velo

pmen

t of

clo

acal

mem

bran

e an

d fa

ilure

of

mig

ratio

n of

mes

oder

mal

m

yoto

mes

and

mid

line

fusi

on.

1. D

efec

tive

fusi

on o

f th

e m

yoto

mes

in th

e m

idlin

e.

2. F

ailu

re of

clo

sure

of

the

exoc

elom

ic sp

ace

with

per

sist

ent h

erni

atio

n of

abd

omin

al

cont

ents

.

Pent

alog

y of

Can

trel

l th

orac

oabd

omin

al e

ctop

ia

cord

is, o

mph

aloc

ele,

clef

t st

ernu

m, d

iaph

ragm

atic

and

pe

rica

rdia

l def

ect

Clo

aca1

exs

trop

hy

exst

roph

y of

blad

der,

impe

rfor

ate

anus

: oft

en

asso

ciat

ed w

ith o

mph

aloc

ele

and

low

er n

eura

l tu

be

defe

ct

Bla

dder

exs

trop

hy

exst

roph

y of

the

blad

der

on

the

ante

rior

abd

omin

al w

all

with

sym

phys

eal s

epar

atio

n

Om

phal

ocel

e de

fect

of

the

ante

rior

ab

dom

inal

wal

l at t

he b

ase

of th

e um

bilic

al c

ord

with

re

sulti

ng h

erni

atio

n of

abdo

min

al c

onte

nts

into

the

umbi

lical

cor

d

bn

wl N

Ta

ble

2. C

HA

RA

CTE

RIS

TIC

S O

F AN

TER

IOR

AB

DO

MIN

AL

WA

LL A

NO

MAL

IES

Pro

gnos

is

An o

m a I y

Str

uctu

ral D

efec

ts

Inci

denc

e K

aryo

tyP

e B

ody

stal

k Sh

ort o

r ab

sent

um

bilic

al c

ord,

1 in

14,

000’

* N

orm

al

Usu

ally

leth

al

anom

aly

com

bine

d w

ith a

ny o

f th

e fo

llow

ing:

ven

tral

wal

l de

fect

, or

abno

rmal

ity o

f th

e lim

bs, s

pine

, fac

e, o

r cr

aniu

m

the

abdo

min

al w

all a

llow

ing

evis

cera

tion

of th

e fe

tal

inte

stin

es

73%

sur

viva

l9*

Gas

tros

chis

is

A r

ight

par

aum

bilic

al d

efec

t of

0.3-

2 in

10,

000’

2 N

orm

al

Usu

ally

leth

al

Pent

alog

y of

T

hora

coab

dom

inal

ect

opia

1

in 1

00,0

00

Tris

omie

s 13

, 18,

and

21

cant

rell

cord

is, p

eric

ardi

al d

efec

t, cl

eft s

tern

um, a

ssoc

iate

d co

ngen

ital h

eart

def

ects

, an

teri

or d

iaph

ragm

atic

de

fect

s an

d su

prau

mbi

lical

an

teri

or a

bdom

inal

wal

l de

fect

E

xstr

ophy

of

the

blad

der,

1 in

200

,000

80

Nor

mal

U

sual

ly le

thal

, but

if

omph

aloc

ele,

impe

rfor

ate

mild

am

enab

le to

su

rgic

al c

orre

ctio

n an

us, a

nd s

pina

l def

ects

A

men

able

to s

urgi

cal

corr

ectio

n w

all a

nd a

nter

ior

blad

der

wal

l A

bdom

inal

con

tent

s, c

over

ed

by p

erito

neum

and

am

nion

, he

rnia

ted

into

the

base

of

the

umbi

lical

cor

d

Abs

ence

of a

nter

ior

abdo

min

al

1 in

40,

000

Nor

mal

Ass

ocia

ted

chro

mos

omal

Pr

ogno

sis

depe

nden

t on

anom

alie

s m

ainl

y pr

esen

ce o

r ab

senc

e tr

isom

ies

13 a

nd 1

8,

but

also

tris

omy

21,

aneu

ploi

dy

and

trip

loid

y A

men

able

to s

urgi

cal

1-3

in 1

0,00

02’

of a

ssoc

iate

d

corr

ectio

n

Clo

aca1

exst

roph

y

Bla

dder

exs

trop

hy

Om

phal

ocel

e


Figure 1. A case of body stalk anomaly demonstrating abdominoschisis and limb defects.

the literature about the exact definition of this condition.91, 96, 137 It has been reported that it can be diagnosed when two of the following are present: exencephaly or encephalocele with facial clefts, thoracoschisis or abdominoschisis, and limb defects?" 137 It has been pointed out, however, that this definition allows the diagnosis to be made in the absence of a ventral surface defect, whch seems counterintuitive?l It has been suggested that an abdominal wall defect must be present to allow the diagnosis?l Because the defect in embryologic development occurs very early (4 to 6 weeks of gestation), this is a very severe abnormality with many associated defects. It is thought that the abnormal development may be triggered by a vascular insult (resulting in ischemia and hemorrhagic necrosis). This vascular hypothesis is supported by a suggested association with cocaine use?O It has been reported that amniotic bands can present in 40% of cases.92 Indeed, it can be difficult to distinguish body stalk abnormality and severe cases of amniotic band syndrome and some investigators feel they may be the same entity with similar cause. Inheritance is sporadic. Body stalk anomaly, unless a mild variant, is not compatible with life.

Prenatal Diagnosis

MSAFP is markedly raised in cases of body stalk anomaly. Ultrasound examination may reveal short or absent umbilical cord; evisceration of the contents of the abdominal cavity (most often left lateral thoracoabdomi- noschisis); associated kyphoscoliosis; caudal regression; limb abnormalities (including partial or complete absence); midfacial clefts; and cranial defects, such as exencephaly, encephalocele, and holocranium. The fetus may appear fused to the placenta. The association with oligohydramnios and severe fetal abnormality may make a comprehensive anatomy survey very difficult.

Differential Diagnosis

talogy of Cantrell, and gastroschisis. Differential diagnosis includes amniotic band syndrome, omphalocele, pen-


Management

Management should be pursued with the knowledge that body stalk anomaly is a lethal abnormality unless in its mildest form. Termination of pregnancy should be offered. If this is not an acceptable management option for parents, expectant management should be pursued with intermittent checks for fetal viability because spontaneous demise may occur. If termination of pregnancy is performed, medical techniques are preferable, to maintain the possibility of fetal autopsy. Parents should be reassured that the recurrence risk is exceedingly small.

Gastroschisis

Background

Gastroschisis, also known as paraomphalocele or abdominoschisis, is a right- sided paraumbilical defect in the anterior abdominal wall (Fig. 2). There are no known teratogens associated with gastroschisis, although it has been noted that there is a markedly higher incidence in teenage m0thers.9~ The defect involves the full thickness of the abdominal wall and consequently there is no parietal peritoneum covering the free loops of intestine that herniate through the defect. The intestine is free to herniate because it is not attached to the posterior abdominal wall and has not undergone the usual bowel rotation and retraction into the abdominal cavity. The embryology of this anomaly is outlined in Table 1. Again, the mechanism is thought to be that of a vascular disruption, involving either the right umbilical vein or right omphalomesenteric artery. Classically, it is small intestine that herniates, but rarely a large defect can occur and other contents of the abdominal cavity can also eviscerate, such as large bowel and 1 i~e r . l~~ There may be associated gastrointestinal abnormalities, such as intestinal atresias.” These atresias are most likely secondary to the actual gastroschisis,

Figure 2. A transverse view of the fetal abdomen demonstrating gastroschisis.


because of such mechanisms as strangulation. The free-floating bowel may become matted and coated with a fibrous exudate or peel. Classically, it has been thought that the fibrous coating is caused by exposure to amniotic fluid, but this mechanism has recently been 35 Inheritance is usually sporadic; however, cases of familial inheritance have been reported, and an autosomal dominant pattern is suggested in these rare instances. Survival may be expected in 73% of Once the lesion has been surgically corrected, long-term prognosis is good, although further medical care for short-gut syndrome may be required. The degree of difficulty for surgical repair, and consequent complications, depends on the size and complexity of the lesion.

Gastroschisis is associated with intrauterine growth restriction.l8p 109 This can be difficult to assess, however, because the abdominal circumference is usually critical to formulas using fetal biometry to estimate fetal weight. Obviously, in gastroschisis the abdominal circumference is reduced because of the absence of intra-abdominal intestine. Raynor and Richards109 demonstrated, in a series of 46 prenatally diagnosed cases of gastroschisis, that the prevalence of intrauterine growth restriction is increased (23%), but is overestimated with prenatal ultrasonography (43%). It is suggested that femur length and head circumference should be used to assess growth in fetuses with gastroschisis.

Prenatal Diagnosis

As discussed previously, both MSAFP and ultrasound are good at detecting gastroschisis prenatally. Both are routinely used; however, the use of MSAFP dates from a time when ultrasound was not as advanced as it is today, and one expects routine ultrasound to be adequate for the diagnosis of gastroschisis. In routine ultrasound surveillance for gastroschisis, the cord insertion to the abdominal wall should be clearly visualized. If there is any doubt, color Doppler imaging should be used to discriminate coiled umbilical cord from possible 'extra-abdominal intestine. In addition, color Doppler demonstrates the mesenteric vessels within the bowel loops (Fig. 3). The defect is almost always to the right of the umbilical cord insertion, although it has been recorded on the left.16 Care should be taken to exclude a membranous sac (to discriminate gastroschisis from omphalocele), and the lack of such a sac is reflected by free-floating bowel loops with an irregular contour (see Fig. 2). Secondary findings in the abdominal cavity are related to the disturbed anatomy secondary to the deficit in intra- abdominal intestine. The usual spatial relationship of remaining intra-abdominal organs may be disturbed resulting in atypical location or relation of such organs as the bladder, stomach, and liver.


The differential diagnosis includes omphalocele; ruptured omphalocele; body stalk anomaly; and normal anatomy, such as umbilical cord artifact. It may be impossible to discriminate a gastroschisis from a ruptured omphalocele. The liver is more commonly extra-abdominal in omphalocele, but this is not pathognomonic. The possibility of a ruptured omphalocele should always be considered when diagnosing a gastroschisis. If any uncertainty persists, a fetal karyotype may be indicated because of the increased incidence of aneuploidy associated with omphalocele.

Figu

re 3

. A

trans

vers

e vi

ew o

f th

e fe

tal

abdo

men

with

col

or D

oppl

er d

emon

stra

ting

the

mes

ente

ric v

esse

ls w

ithin

the

gast

rosc

hisi

s.

Figu

re 8.

A tr

ansv

erse

vie

w o

f the

bla

dder

sho

win

g a

sing

le u

mbi

lical

arte

ry (d

emon

stra

ted

by o

nly

one

arte

ry p

assi

ng a

roun

d th

e fe

tal b

ladd

er).

Figu

re 9

. An

um

bilic

al c

ord

cyst

(co

lor

Dop

pler

dem

onst

rate

s th

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958 ROBINSON & ABLJHAMAD

Management At diagnosis of gastrosclusis, adequate counseling should be provided,

and coordinated care organized with a pediatric surgical team. Chromosomal abnormality is rarely associated with gastroschisis. In cases of isolated gastroschisis, invasive testing for fetal karyotype is generally not indicated. The parents should be informed of the long-term prognosis. Interaction with patient-help groups may be useful in this regard. In a recent series, 96% of those available to follow-up (with an average age of 16) were in good health with normal growth.34 Delivery should be planned at a site where such a pediatric surgery team is available. If the parents do not wish to continue with the pregnancy, there is no specific termination management protocol required for this condition.

The pregnancy should be monitored with serial ultrasound, both for surveillance of the gastroschisis and to monitor fetal growth. The possibility of intestinal perforation and meconium peritonitis should always be entertained and consequently care should be taken to look for intra-abdominal calcifications. Many investigators have looked for prenatal findings that may be prognostic for neonatal outcome or that may warrant early interruption of the ~regnancy.~, 6, 11,

32, n, ~ 6 , 136 Surprisingly, the size of the abdominal wall defect does not affect the outcome.ll Bowel thickening has been associated with poor outcome.n There are contradictory reports regarding bowel dilatation?, 6, 24, 86 Intestinal dilatation of greater than 17 mm has been reported as having a positive predictive value of 67% for bowel atresia." Similarly, it has been reported that a bowel diameter of greater than 10 mm between 28 and 32 weeks' gestation is the best predictor of poor neonatal outcome? Other investigators, however, have not found bowel dilatation to be a significant prognostic finding." 86 If bowel diameter is used in managing gastroschisis, caution should be taken to ensure that small bowel, and not large bowel, is being measured. When Doppler velocimetry of the superior mesenteric artery was studied in gastroschisis, it was not found to be predictive of outcome?

As long as prenatal surveillance remains reassuring, it can be planned to deliver a fetus with gastroschisis at term. Preterm delivery to improve neonatal outcome has not been found to be benefi~ial.3~ The recommended mode of delivery remains contr~versial.~~, 37, 43, 82, 94, 1 1 ~ , 135 Although some investigators have reported delivery by cesarean section to be 82, ll2, lZo, 135 others have refuted this.17, ~ 3 , 94, lol It may seem intuitive that a vaginal delivery may be more traumatic and deleterious to exposed organs. This is commonly accepted in cases where the liver is known to be extracorporeal, and in this instance cesarean delivery is widely practiced. In cases of extrusion of only bowel, however, findings regarding bowel injury and neonatal outcome have differed between researchers, and there can be no consensus recommendation. It is of note that one group that practices trial of labor for gastroschisis has reported the rate of intervention with cesarean delivery to be high (37%).8

Whatever the mode of delivery, great care should be taken with handling of the bowel at birth. It should be kept warm and moist, and care should be taken to avoid lying the baby in the prone position with the bowel draped to one side because this can lead to kinking of the superior mesenteric artery and consequent bowel ischemia and necrosis.

Pentalogy of Cantrell

Background Pentalogy of Cantrell, also known as Cantrel-Huller-Ravitch syndrome, thora-

coabdominal ectopia cordis, and peritoneopericardial diaphragmatic hernia, is exceed-


ingly rare. The major defect is that of a cleft sternum with ectopia cordis (Fig. 4), but there is often associated anterior abdominal wall, anterior diaphragmatic, and intracardiac defects. There may be many other associated congenital anomalies, and in particular an association with midline defects, such as cleft lip, with or without palate, and midline encephalocele has been reported.26 Cystic hygroma has also been associated in several cases.66 The embryology of this condition is described in Table 1. It has been postulated that the cause may be of vascular origin, although monozygotic twinning has also been suggested as a possible contributory mechani~m.3~ There are no known teratogens associated with this condition. Inheritance of this condition is sporadic, although there is one report in the literature of three brothers with extensive diaphragmatic defects, two of whom had pentalogy of CantreKS9 There may be an associated aneuploidy (13, 18, or 21).76

There is controversy in the medical literature regarding the prognosis of pentalogy of Cantrell.Z9* 41, 49, Some authors regard it as a uniformly lethal abnormality, whereas others consider it appropriate to contemplate corrective surgery. One series of 10 prenatally diagnosed cases has been reported with a universally fatal In this manuscript, the authors reviewed the published literature on prenatally diagnosed cases of pentalogy of Cantrell and documented a universally fatal 0utcome.4~ Other centers, however, have reported their experience with treating this condition. In a recent report of four cases of pentalogy of Cantrell, two neonates were treated with corrective surgery41; however, only one case survived. There are other reports of successful corrective

and one institution has reported successful corrective surgery (with the children surviving beyond infancy) in four of eight cases.64 In assessing any possibility of viability, particularly if the case is a mild variant, one should consider any associated intracardiac lesion very carefully, because associated intracardiac anomalies are common and have a profound bearing on prognosis.

Figure 4. Ectopia cordis. The two cardiac ventricles can be seen in the center of the picture, with the apex of the heart pointing toward the transducer.


Prenatal Diagnosis

MSAFP is raised in cases of pentalogy of Cantrell because of the ectopia cordis and anterior abdominal wall defect. The primary means of prenatal diagnosis, however, is ultrasound examination. The heart is often totally outside the chest with the cardiac apex in a cephalic orientation. As a result of the displaced heart, the thorax is smaller than normally expected. Cases have been reported with ultrasound diagnosis as early as 10 and 11 weeks of Because of the severity of this condition, diagnosis is often obvious. It should be borne in mind, however, that there can be mild variants. The discovery of any of the associated abnormalities should precipitate a detailed search for this condition. In particular, if an omphalocele and pericardial effusion have been found in combination, it is recommended that great care be taken to rule out a variant of pentalogy of Cantrell.lm If this condition is diagnosed, an exhaustive search for associated intracardiac lesions should be performed.


body stalk anomaly, and amniotic band syndrome. The differential diagnosis includes omphalocele, isolated ectopia cordis,

Management

Once a case of pentalogy of Cantrell is diagnosed, the parents should receive extensive counseling. The counseling should be multidisciplinary and be carried out in conjunction with a pediatric surgery team. Because of the possible associated aneuploidies, a fetal karyotype may be obtained. It may be preferable to obtain the karyotype by amniocentesis because although amniotic fluid AFP is expected to be markedly elevated, an acetylcholinesterase level may suggest a subtle neural tube defect not diagnosed by ultrasound. A fetal echocardiogram should be obtained, because of the prognostic importance of associated intracardiac abnormalities. If the parents decide not to continue with the pregnancy, termination can be performed either by surgical or medical means. If after appropriate counseling, however, the parents decide against such intervention, the pregnancy can be followed expectantly. Regular ultrasound evaluation may be performed for surveillance of the fetal anomalies. Bearing in mind the grim prognosis, it is appropriate to guide the parents toward minimum intervention, particularly regarding fetal monitoring and mode of delivery. Parents should be reassured that recurrence risk is exceedingly small.

Cloacal Exstrophy

Background

Cloacal exstrophy, although similar to bladder exstrophy, is a much more severe abnormality. The early occurrence of the embryologic abnormality and the observation of the lesion in monozygotic twinsso have led investigators to speculate that both of these are manifestations of the same disturbance of early blastogenesisso (similar observations have been made for pentalogy of Cantrell).39 Failure of development of cloaca1 membrane and failure of formation of the urorectal septum and defective fusion of the mesodermal myotomes leads to the association of exstrophy of the bladder, omphalocele, imperforate anus, and neural tube defects. This condition is also known as extrophia splanchnica and


omphalocele, exstrophy, imperforate anus spinal defects syndrome. There is associated failure of fusion of the pubic rami. There may be other associated abnormalities, particularly of the genitourinary and renal systems. It is exceedingly rare with a reported incidence of 1 in 200,00022 Because of the severity of this condition, survivors do not have preserved reproductive function and, although possible, genetic inheritance is unknown. Cloaca1 exstrophy has been reported in siblings from separate pregnancies and consequently a genetic basis of inheritance is fea~ib1e.I~~ To date, the occurrence of this condition is considered to be sporadic. There are no known teratogens associated with this condition.

Prenatal Diagnosis MSAFP is elevated in cloacal exstrophy, as is amniotic fluid acetylcholines-

terase. Ultrasound examination, however, is the primary technique for diagnosis of this condition. The most obvious abnormality in this syndrome is the omphalocele. If an omphalocele is observed, an exhaustive search should be carried out for the other features of this syndrome. If there is no omphalocele, which is the case in a significant proportion, the diagnosis of this condition can be considerably more difficult. The cloacal exstrophy itself may not be visualized, although it can be inferred from the inability to visualize the bladder in the presence of normal amniotic fluid volume. If there is uncertainty about the position of the bladder, interrogation of the umbilical arteries with color Doppler may help locate its position. When the fetal abdomen is viewed in a sagittal plane, an irregular anterior mass may sometimes be visualized. Interestingly, cloacal exstrophy can be first diagnosed, either as a soft tissue mass105 or cystic structure in the pelvis, which eventually disappear^.^^ The differential diagnosis for a cystic structure includes that of cloacal cyst; however, it should be noted that cloacal cysts are not an associated finding of omphaloceles. Any of these findings should initiate an extensive anatomy survey, both for cloacal exstrophy but also for possible associated abnormalities. In particular, a detailed search for 'a neural tube defect (amniotic fluid acetylcholinesterase may be of use if there is difficulty); abnormalities of the kidneys; and abnormalities of the external genitalia (if male). It may also be noted that the legs are in an abnormal position secondary to significant symphiseal diathesis.

The finding of a pelvic cystic structure, which goes on to disappear, in this anomaly is of particular interest, because it appears to challenge the currently accepted theory for the formation of cloacal exstrophy. The formation of a cystic structure, which then disappears, is suggestive of rupture of the urorectal septum rather than failure of formation of such a septum. This apparent discrepancy between clinical finding and scientific theory is yet to be resolved.


amniotic band syndrome. The differential diagnosis includes omphalocele, body stalk anomaly, and

Management

In most cases of cloacal exstrophy, the condition is incompatible with life and termination of pregnancy should be offered. In milder cases, surgical correction may be attempted at birth. If the latter management is being contemplated, the parents should be extensively counseled (with pediatric involvement) as to the nature of the multiple, extensive surgeries that are required and the quality of


life to be expected if the baby survives. There is no specific obstetric management protocol either for continuation or termination of pregnancy.

Bladder Exstrophy

Background In bladder exstrophy, also known as exstrophy-epispadias complex, the failure

to develop a cloacal membrane and failure of midline fusion of the myotomes leads to a defect in the covering of the urogenital system. The defect may be mild, only being clinically apparent as an epispadias, or it may be very significant with complete exposure of the posterior bladder wall. A case with bladder exstrophy but intact anterior abdominal wall (diagnosed postnatally) has been described.= Because the urorectal septum develops normally, there is no gastrointestinal involvement. As in cloacal exstrophy, however, there may be separation of the pubic rami. There may be associated or secondary renal abnormalities. Bladder exstrophy is much more common than cloacal exstrophy, with an incidence of approximately 1 in 40,000. It is two to three times more common in boys. There are no teratogens associated with this condition. The inheritance is multifactorial, and the chance of an affected parent having an affected child has been quoted as 1 in 70 and the recurrence risk as 1%.lZ6 At least 18 familial cases have been identified in the literature.93

Prenatal Diagnosis

The MSAFP may be markedly raised. This is of importance in the diagnosis of bladder exstrophy because the ultrasound diagnosis may not be obvious. Certainly, in the presence of an unexplained elevated MSAFP the fetal urinary bladder must be documented on ultrasound examination. As in cloacal exstrophy, the exstrophy itself may not be easily visualized but can be inferred from the absence of the bladder in the presence'of normal amniotic fluid volume. To confirm an absent bladder, prolonged examination is required in case it is just transiently empty. Color Doppler interrogation of the umbilical arteries may be useful to identify where the bladder should be. On sagittal view of the anterior abdominal wall a small mass, representing the extruding posterior bladder wall, may be visualized. Separation of the pubic rami may be reflected by abnormal widening of the iliac crests. The umbilical cord insertion may be lower than expected, and the external genitalia (if male) may be higher than expected.

Diagnosis of bladder exstrophy prenatally is difficult. In a retrospective series of 25 babies born with bladder exstrophy, it was found that 17 of the pregnancies had undergone ultrasound examination, but only 3 cases had been identified.46 When the ultrasound images were reviewed it was noted that the bladder was not visualized in 12 (71%) of 17 cases, a lower anterior abdominal bulge was noted in 8 (47%), of 17 cases, anteriorly displaced genitalia was identified in 8 (57%) of 14 boys, the umbilical cord insertion was low in 5 (29%) of 17 cases, and there was abnormal widening of the iliac crests in 3 (18%) of 17 cases.


siently empty normal bladder. The differential diagnosis includes omphalocele, cloacal exstrophy, and tran-


Management

The surgical correction of bladder exstrophy involves a staged approach. As such, many operations are performed over a long period.45 Urinary continence is achieved in most cases. There may be significant abnormalities of the external genitalia and in extreme cases gender reassignment may be considered. This medical ordeal imposes considerable strains on the chldren involved and their parents.*32 This information should be imparted to the parents during extensive prenatal counseling with a multidisciplinary approach. If the parents decide to terminate the pregnancy it is preferable to use medical means for postnatal confirmation of prenatal findings. If the parents decide to pursue the pregnancy, no alteration in pregnancy management or mode of delivery is indicated.

Omphalocele

Background

Omphalocele (Fig. 5), also known as exomphalos, results from failure of the normal closure of the exocelomic space with persistent herniation of abdominal contents into the base of the umbilical cord. The omphalocele may contain just intestine; however, larger defects often contain liver and very large defects containing many intra-abdominal organs can occur. As in gastroschsis, the normal developmental bowel rotation does not occur. Omphalocele can also result from failure of midline fusion of the myotomes. In the latter mechanism, there is often etiologic overlap with other syndromes, such as cloaca1 exstrophy and pentalogy of Cantrell. The incidence of omphalocele is 1 to 3 in 10,000.27 Omphaloceles are associated with both other structural (50%)" and chromosomal abnormalities (approximately 50%).92, 98 Most often, associated structural abnor-

Figure 5. A transverse view of the fetal abdomen demonstrating a large omphalocele, with the stomach herniating with the other small intestines.


malities are in the heart, where any of a wide spectrum of intracardiac and aortic anomalies may be The major association of cloacal exstrophy and pentalogy of Cantrell is discussed previously; however, there are many other associated abnormalities, including neural tube defects, facial clefts, and abnormalities of the renal, gastrointestinal, and skeletal systems. The associated chromosomal abnormalitie~~~, 98 are most frequently trisomies of 13 and 18; however, trisomies of chromosome 21 and triploidy can occur. If the omphalocele contains only or if there is oligohydramnios or polyhydrarmios,102 an associated chromosomal abnormality is more likely. There are no known teratogens associated with omphalocele, although it has been recently suggested that misoprostol exposure is a possible teratogen.a Inheritance of this condition is usually sporadic with a recurrence risk of less than 1%.

Prognosis for omphalocele depends greatly on whether or not there is an associated chromosomal abnormality. The surgical repair can be immediate, delayed, or staged depending on the size of the lesion.'4o In isolated lesions, with no associated chromosomal abnormality, survival rates are excellent (>90%),w3 92

although there may be surgical complications through childhood79 and indeed in later life.

Prenatal Diagnosis

As stated previously, MSAFP is elevated in 89% of fetuses with omphalo- ~ e l e ~ ~ and more than 90% should be picked up with ultra~ound.~~ Both techniques are good to screen for omphalocele. As with gastroschisis, with today's technology, ultrasound alone should detect most omphaloceles. The ultrasound appearance of omphalocele differs from gastroschisis in that the abdominal contents are enclosed (rounded and not free floating); the lesion is located at the base of the umbilical cord (rather than to the right of the insertion); and the liver is often included. This lesion cannot be diagnosed before the end of the 12th week of pregnancy because it is normal for the bowel to herniate into the cord before this time. Also, the converse can happen after 12 weeks, when omphaloceles can transiently reduce during an examination. It should be noted that a true umbilical hernia is indistinguishable from an omphalocele. Color Doppler interrogation of the umbilical cord can help locate the exact site of the defect. If the diagnosis of omphalocele is suspected, it is important to look for an acute angle between the fetal abdomen and the origin of the sac on a transverse plane (see Fig. 5). This reduces the chance of the finding being artifactual secondary to an oblique imaging plane or excessive transducer pressure.

If an omphalocele is diagnosed, as with every abnormality, an exhaustive search should be carried out for associated anomalies. In the case of omphalocele, particular care should be taken to look for other structural defects associated with trisomies 13 and 18. In particular, a sagittal profile of the face should be obtained and the heart, fingers, and feet should be imaged carefully.


The differential diagnosis includes normal physiologic herniation before 12 weeks; gastroschisis; umbilical hernia; cloacal exstrophy; Beckwith-Weidemann syndrome; and artifactual finding (pseudo-omphalocele).


Management

If an omphalocele is diagnosed a detailed examination for other associated abnormalities is performed. Because of the considerable difference in prognosis if there is an associated chromosomal abnormality, genetic counseling is appropriate and a fetal karyotype should be obtained. A fetal echocardiogram should also be performed. If other structural abnormalities are discovered, counseling has to be tailored to the specific situation. Counseling should be multidisciplinary and involve the pediatric surgical team. If the parents opt for termination of pregnancy, a medical method is preferred in the presence of multiple anomalies for potential postnatal correlation of prenatal findings. Otherwise, pregnancy management does not differ from that of a normal pregnancy. Serial ultrasound examinations may be performed for surveillance of the abnormality. Mode of delivery is less controversial than for gastroschisis and the aim should be for a normal vaginal delivery:7* 83, 85 unless other factors intervene. In cases of giant omphalocele, however, especially containing liver, it may be reasonable to per- form cesarean delivery at term to avoid dystocia.

Beckwith-Wiedemann Syndrome

The Beckwith-Wiedemann syndrome, also known as exomphalos-rnacroglossia- gigantism syndrome, is the association of omphalocele, macrosomia, organomegaly, macroglossia, and neonatal hypoglycemia. Omphalocele is present in most cases, and this syndrome should be considered whenever an omphalocele is diagnosed. It should be noted, however, that an omphalocele is not obligatory to the diagnosis: this syndrome should also be considered if macroglossia or any organomegaly is noted on ultrasound examination. Most cases are sporadic, but it can be autosomal dominant with variable transmission in inheritance. The management of this syndrome is similar to that of omphalocele.

UMBILICAL CORD

Background

The normal embryologic development of the umbilical cord is described at the beginning of this article. At the end of embryologic development, the umbilical cord consists of the umbilical vein and two umbilical arteries covered by amnion. The amnion is closely adherent to the cord and cannot be elevated from it. The cord is surrounded in Wharton's jelly (a mucopolysaccharide gel). The normal cord length is approximately 55 cm95 with a diameter of approximately 1 to 2 cm.28 Cord lengths of up to 300 cm7 and diameters of greater than 3 cmZ8 have been reported in normal pregnancies. A normal cord also has a helical structure, with the average number of helices being 11, but as many as 380 have been re~0rded.l~ In most cases, these helices are to the fetal left. It has been suggested that both length and helical pattern are related to fetal movement. Short cords can be associated with conditions with decreased fetal movement, such as oligohydramnios and breech pre~entati0n.l~ There has been much debate as to the origin of the direction of the helices. Although theories based on fetal "handedness" and the earth's rotation have been aired, it is likely that the larger size of the right umbilical artery and associated hydrostatic pressure


initiates the spiral effect.78 It has been reported that straight cords without helices are associated with adverse perinatal

The umbilical cord is studied with ultrasound prenatally. It can be visualized in the longitudinal or transverse plane. In the transverse plane, the two smaller arteries can be seen in relation to the larger vein, as the ears to a "Mickey Mouse face" (Fig. 6) . Some investigators, however, like to use color Doppler to delineate the number of vessels in the cord, which can be done by showing the arteries diverge around the fetal bladder because this finding infers the presence of two umbilical arteries. This latter technique can lead to overdiagnosis of a single umbilical artery because the two arteries may fuse before the fetal cord origin; however, it is a widely accepted and practiced techmque. The cord insertions at both the fetus and the placenta should be visualized at routine ultrasound examination; the former to rule out defects of the anterior abdominal wall and the latter to rule out such abnormalities as a velamentous cord insertion (which can be associated with intrauterine growth restriction). Because of the association of a straight cord with adverse perinatal it should be observed if the cord has the normal helical appearance or not (a straight cord is shown in Figure 7). Although abnormalities of cord length can also be associated with complications of pregnancy,14 measurement of cord length at ultrasound examination may be impractical. Doppler velocimetry studies of both the umbilical arteries and vein may be carried out to assess placental function and fetal well- being. This article, however, is limited to structural assessment alone.

Single Umbilical Artery

A single umbilical artery, if present, should be detected on routine obstetric ultrasound examination (Fig. 8). A single umbilical artery may result from atrophy of an existing vessel or by lack of formation of another artery in the first place. It has been reported that the left artery is more commonly absent than the right; moreover, absence of the left umbilical artery is more likely to be associated with fetal anomalies? Associated fetal anomalies have been reported in 20%57 to 50%Io3 of cases of single umbilical artery. Chromosome abnormalities may also be associated with this finding.% Associated aneuploidies include trisomies of 13 and 18 and triploidy (associated trisomy 21 being uncommon).121

Figure 6. A transverse view of a three-vessel cord.


Figure 7. A straight umbilical cord.

Associated structural anomalies can be found in any organ system of the fetus and in some cases there may be multiple anomalies. This finding should always precipitate a detailed anatomy survey and consideration should be given to obtaining a fetal karyotype (either by amniocentesis or chorionic villous sampling). The decision to obtain a fetal karyotype should depend in large part on the presence or absence of additional malformations. At least one investigator has reported an association with intrauterine growth re~triction~~ and consideration may be given to third-trimester ultrasound examination to assess fetal growth.

,Persistent Right Umbilical Vein

The right umbilical vein, if present, runs through the fetal abdomen to the right of the gallbladder and may join the right portal vein or enter directly into the right atrium. The right umbilical vein persists when there has been involu- tion of the left umbilical vein. The original description of this anomaly, in a series of six, suggested that there may be other associated structural anomalies and recommended detailed ultrasound anatomy survey when found.n More recent reports, however, suggest that this is a more common finding than previously realized and is not as sinister a finding as originally ~uspected.'~, lz7

The incidence of persistent right umbilical vein is approximately 1 in 400.19 The most recent report (and the largest reported series) suggests this finding to be benign, with only one of the 69 fetuses with a persistent right umbilical vein having a major anomaly. Indeed, because of the subtle nature of this finding, it may often be overlooked.

Cord Masses

Umbilical Cord Cysts

Umbilical cord cysts are often irregular in shape, are located in the central part of the cord between the blood vessels (Fig. 9), and usually resolve by the end of the first trimester."* The prevalence of cysts in the first trimester is


approximately 3%.l18 True cysts are vestiges of the allantoic or omphalomesenteric duct. Pseudocysts are localized fluid collections in Wharton’s jelly. True cysts have an epithelial lining and are located, more commonly, near to the fetal insertion of the umbilical cord. They range from 4 to 60 mm in size.118 True cysts have been reported to be associated with omphalocele,42 patent urachus,” hydronephrosis,lzz and Meckel’s divertic~lum.~~ Pseudocysts are associated with omphalocele, hemangiomas, or chromosomal abnormalities.*70, 75, 108, It is of note that pseudocysts have been reported on a number of occasions in association with trisomy 18.68, lo8, Pseudocysts do not have an epithelial lining (the true diagnosis may often be made retrospectively with histologic confirmation); are more common than true cysts; and are also most commonly located near the fetal cord insertion.l18 In more than 20% of cases of umbilical cord cysts (of either type), there are associated chromosomal or structural anomalies.l18 The longer the cyst persists in pregnancy, the more likely it is to be associated with an associated anomaly. It is thought that true cysts are more likely to persist than pseudocysts.l18

Umbilical cord cysts are often located near the fetal insertion of the umbilical cord. When routinely visualizing this area during an anatomy survey (to rule out ventral wall anomalies) it is simple to carry out a cursory inspection for such cysts. If suspected, color flow may be used to clarify the cyst and accurately delineate their location. These cysts may be more easily seen in the first trimester because of the relative size of the cyst to the cord vessels. If located, follow-up ultrasound examinations should be carried out to find if the cyst resolves or not. If not, the stronger association with anomaly should be considered and imparted to the patient at counseling. Consideration should be given to obtaining a fetal karyotype and certainly a minimum of a detailed second-trimester ultrasound should be performed.

Umbilical Cord Varix Umbilical cord varix (Fig. lo), also known as umbilical vein ectasia, can occur

in the intra-amniotic or intra-abdominal portion of the umbilical vein. It is simply a cystic dilatation of the umbilical vein. There are numerous case reports in the literature.’” 113* 139, 141 The two larger case series in the literature give conflicting reports as to the prognosis of this lesion.40,87 One series of five cases reports good perinatal outcome in all five.4o The other series of nine cases, however, reports subsequent demise in four of the cases (one with trisomy 21).87 There is certainly a potential for adverse fetal outcome because there may be a vascular steal effect and left ventricular cardiac strain, or failure, secondary to a state of high cardiac output. If the umbilical cord varix does not impose any prenatal problems, it is most likely to resolve postnatally because after birth blood flow through the umbilical vein ceases. The cystic structure collapses postnatally secondary to the lack of blood

When first visualized with gray-scale ultrasound, this anomaly appears as a simple cystic structure, either in the umbilical cord or in the fetal abdomen below the cord insertion. When interrogated with color Doppler, however, marked turbulent flow is noted through the lesion in direct continuity with the umbilical vein (see Fig. 10).l13 Because of the series of cases with poor perinatal

we recommend follow-up with regular fetal testing and thrd-trimester growth scans.

Umbilical Cord Tumors Tumors of epithelial cell origin can occur in the umbilical cord. Although

rare, the two major classes of tumors that can be found on the umbilical cord


are hemangiomas and teratomas. In contrast to umbilical cord cysts, tumors are often found at the placental end of the umbilical cord.lZ8 In contrast to umbilical cord masses of vascular origin, tumors are usually echogenic in nature. Any type of tumor can lead to cord obstruction, vascular compromise, and shortening of the cord; angiomas can lead to high cardiac output states with resulting cardiac failure and hydrops. Angiomas in particular can be associated with very high levels of AFP.'O6> no If a tumor of the umbilical cord is detected, serial ultrasound scans should be carried out to monitor fetal growth and well-being. In particular, if an hemangioma is suspected, tricuspid regurgitation, right atrial enlargement, and the signs of hydrops should always be looked for. If there is concern about possible constriction of the umbilical vessels, regular interrogation of both the artery and vein should be performed with pulse Doppler.

Other Vascular Anomalies of the Umbilical Cord

There are other very rare vascular abnormalities of the umbilical cord that have been reported. These include an arteriovenous malformation of the umbilical cord (which resulted in disseminated intravascular coagulopathy of the fetus)111; umbilical cord aneurysms, both arteria1lZ9 and venouslZ8, 138; and persistent vitelline artery.lZ4 Umbilical cord hematomas can also occur: these can be iatrogenic, secondary to an invasive prenatal pr~cedure,"~, 134 but have also been reported of spontaneous 0r ig in ,2~ ,~~~ and in association with a cord cyst." What- ever the cause of the hematoma, the prognosis can be very poor with resulting fetal demise.", 31, Cord thrombosis has also been reported,', 13, 31 both arterial (with the thrombosis extending into the fetal aorta) and venous (resulting in fetal demise).', l3 If any of these vascular abnormalities are detected, it is prudent to follow the pregnancy with serial ultrasound to monitor fetal growth and well- being. Again, if an arteriovascular malformation or aneurysm is detected, routine ultrasound surveillance should also look for tricuspid regurgitation, right atrial enlargement, and the signs of hydrops.

ABNORMALITIES OF CORD INSERTION, POSITION, AND COURSE

Velamentous Insertion

A velementous cord insertion is where the umbilical cord inserts into a point away from the placenta and the vessels then pass to the placenta across the membranes (between the amnion and chorion) with no surrounding protec- tive tissues (Fig. 11). This condition is associated with intrapartum complications and low birth weight.38 It is of note, however, that prenatal ultrasound is very poor at detecting this condition with only 1 of 80 being detected in the largest published ~eries.5~ It should be noted that velementous cord insertion has been diagnosed prenatally with ultrasonographylOO and that the association of a lower MSAFP and higher maternal serum human chorionic gonadotrophin with this condition has also been made.60 If a velementous insertion is detected, serial third-trimester ultrasound should be instituted, as required, to follow fetal growth.


Figure 11. A velementous cord insertion with the cord insertion separate from the placenta (the vessels joining the placenta across the intervening membranes).

Vasa Previa

Vasa previa occurs when a velementous cord insertion, or vessels running in the membranes between a placenta and succenturiate lobe, pass in front of the presenting part of the fetus (Fig. 12). This is obviously a very high-risk situation because these vessels may be ruptured, either spontaneously or artifi- cially during labor. This condition can be detected antenatally both by abdominal:6 vaginal,lM or transperineaP ultrasound examination. Color Doppler can be used to follow the course of the vessels and pulse Doppler can be used to calculate the pulse in an arterial vessel and determine if the vessel is truly fetal in origin. This abnormality can be detected prenatally on routine ultrasound. The internal cervical 0s should be visualized routinely on any ultrasound examination to make the diagnosis of placenta previa possible. If a series of gray lines are seen in the vicinity of the internal cervical os, the diagnosis of vasa previa should be entertained. This can be followed-up with transvaginal, color, and pulsed Doppler interrogation as required. Using this strategy, a recent series diagnosed 18 cases of vasa previa.8l In this series the mean gestational age of diagnosis was 26 weeks and the diagnosis was made as early as 15.6 weeks. This information can be used in the prenatal management of the pregnancy, usually resulting in cesarean section after the confirmation of fetal lung maturity (if the abnormality persists on follow-up ultrasound examination). The authors believe that an endovaginal ultrasound with color flow Doppler should be performed on every pregnancy with a succenturiate lobe given the increased association with vasa previa.

Funic Presentation and Cord Prolapse

When the umbilical cord lies in front of the fetal presenting part (i.e., the umbilical cord is the presenting part) it is known as afunic presentation (Fig. 13).


This is of concern because if the membranes rupture, there is an increased likelihood of a cord prolapse. Indeed, occult cord prolapse has been diagnosed with both gray-scale ultrasound53 and color Doppler.” Prolapse of the umbilical cord is considered to be an obstetric emergency. Prenatal diagnosis of a funic presentation of the umbilical cord was first described by Raga et al.Io7 The diagnosis of t h s abnormality in the presence of ruptured membranes should lead to hospital admission and bed rest with cesarean section being indicated at the onset of labor, fetal distress, or cord prolapse. Management options, when the diagnosis is made in the presence of intact membranes, are less clear, because the funic presentation may resolve spontaneously or be reduced by the presenting part with the onset of labor.

Nuchal Cord

A nuchal cord, when the umbilical cord has wrapped itself around the fetal neck, at least one time and often more, can be detected with prenatal ultrasound examination (Fig. 14). This was first described by Joupilla and Kirkinen.74 This abnormality can be suspected on gray-scale ultrasound with the direct visualiza- tion of the cord, or by indentations on the sagital profile of the fetal neck, and can be more clearly imaged with color Doppler sonography. A large prospective study of 180 random patients demonstrated that color Doppler imaging had a sensitivity of 93% when used in t h s application after 36 weeks of ge~tat ion.~~ There is greater accuracy for this investigation when there are multiple nuchal cords and for when the test is carried out close to delivery, presumably, in both cases, because in these instances the nuchal cord is less likely to spontaneously reduce.71 The difficulty with this diagnosis is the lack of a clear definitive management plan once the diagnosis is made. A nuchal cord, single or multiple, is a very common diagnosis at normal vaginal delivery and is most often not associated with any abnormality. Intervention based on this finding alone is not

Figure 14. A nuchal cord.


warranted. It is prudent to follow-up such cases with rigorous fetal testing, however, including Doppler velocimetry studies of the umbilical vein and artery.

Umbilical Cord Knots

True knots of the umbilical are rare but can be associated with adverse perinatal outcome.20 A true knot is formed when fetal movement causes the fetus to pass through a loop of cord. This is more likely to occur early in pregnancy when there is proportionally more amniotic fluid and the range of fetal movement is greater. In contrast, false knots are more common and are not associated with adverse perinatal outcome.61 False knots are formed by a focal bulge in the cord or exaggerated looping of umbilical vessels. It is thought that false knots result from the umbilical vein being comparatively longer than the umbilical arteries. Close inspection is required to discriminate between the two types of knot. Unfortunately, prenatal ultrasound is not good at detecting umbilical cord knots (Fig. 15). Sepulveda et all" retrospectively examined 18 cases in which a true umbilical knot was found at delivery. All of the parturients in this series had a normal second-trimester scan in which no cord abnormality was detected. Moreover, in two cases where a diagnosis of true knot had been entertained prenatally, at delivery only a false knot was found in one and no abnormality was found in the other.

The concern when a true umbilical cord knot is present is that there is constriction of the umbilical cord vessels if the knot tightens. If cord occlusion is suspected, pulse Doppler velocimetry studies should be used to assess the blood flow in the umbilical vessels. Abnormal venous Doppler waveform has been demonstrated in a case of true umbilical cord kn0t.4~ Similarly, other cases of cord constriction have been demonstrated with abnormal Doppler arterial waveforms.2 115,

Figure 15. A transverse view of an umbilical cord knot.


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abdominal wall and umbilical cord anomalies

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