soap bubble

Indian Journal of Pediatrics, Volume 72—May, 2005 403

Symposium on Common Pediatric Surgical Problems-II

Correspondence and Reprint requests : Dr. Arun Kumar Gupta,Professor, Department of Radiodiagnosis, All India Institute ofMedical Sciences, New Delhi-110029. Fax : 91-26588641, 26588663

A wide spectrum of congenital anomalies may affectgastrointestinal tract, some of which manifest early afterbirth while others may not present till late childhood oradulthood. Imaging plays a very useful role in thesedevelopmental lesions, most of which present withobstruction. In most cases, plain radiography,gastrointestinal contrast study or Ultrasound (US) suffice.Computed tomography (CT) and Magnetic ResonanceImaging (MRI) are increasingly proving more useful toprovide an accurate diagnosis specially in difficult cases.

Developmental lesions of the neonatal gastrointestinaltract can be grouped as follows: 1

Structural

Attributed to embryologic maldevelopment• Esophageal atresia with or without fistula• Antro-pyloric atresia• Antral diaphragm• Duodenal atresia• Duodenal stenosis

Intrinsic: windsock duodenum Extrinsic: annular pancreas

• Midgut malrotation with peritoneal bands• Duplication or mesenteric cyst• Anorectal atresia

Imaging of Congenital Anomalies of the GastrointestinalTract

Arun Kumar Gupta and Bhuvnesh Guglani

Department of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India.

Attributed to in utero vascular (ischemic) complication• Jejuno-ileal atresia• Colonic atresia or stenosis• Complicated meconium ileus

Functional

• Meconium plug syndrome and its variants• Megacystis-microcolon-intestinal hypoperistalsis

Structural and Functional Combined

• Hypertrophic pyloric stenosis• Midgut vovulus (complicating midgut

malrotation)• Uncomplicated meconium ileus• Colonic aganglionosis

In a normal neonate, swallowing begins almostimmediately after birth and gas should be present in thestomach within few minutes.3 Within 3 hours of birth, theentire small bowel usually contains gas while the sigmoidcolon is seen only after 8-9 hours.4 Disruption of thiscommon pattern is seen in obstruction or presence ofunderlying illness such as brain damage, septicemia orhypoglycemia.

Plain radiograph is a useful, simple and mostinexpensive tool in the evaluation of the neonate withgastrointestinal (GI) obstruction. Unlike adults and olderchildren, in neonates the small and large bowel usually

Abstract. The radiological imaging plays a vital role in the evaluatin of patients with congenital anomalies of thegastrointestinal tract. The evaluation of these patients, most of which present early after birth, frequently requires the use ofvarious imaging modalities for making the correct diagnosis and planning surgical correction. This article reviews the commoncongenital anomalies of the gastrointestinal tract including obstructive lesions, anomalies of rotation and fixation, anorectalanomalies, and intestinal duplications. The plain radiograph is often diagnostic in neonates with complete gastric of upperintestinal obstruction and further radiologic evaluation may be unnecessary. An upper gastrointestinal series should beperformed in all patients with incomplete intestinal obstruction. Sonography is useful in the evaluation of many congenitalanomalies affecting pediatric gastrointestinal tract especially hypertrophic pyloric stenosis, enteric duplication cysts, midgutmalrotation, meconium ileus and meconium peritonitis. Moreover, CT and MRI has assumed a greater importance as theseprovide excellent anatomic details which may be necessary for correct diagnosis as well as treatment planning. This isparticularly true in evaluation of congenital anomalies such as esophageal/enteric duplications, vascular rings and anorectalanomalies. It is important to be familiar with the role nad usefulness of the various imaging modalities so that these can be usedjudiciously to avoid unnecessary radiation exposure while minimizing the patient discomfort.[Indian J Pediatr 2005; 72 (5) : 403-414]

Key words : GIT; Congenital anomalies; Intestinal abnormalities


404 Indian Journal of Pediatrics, Volume 72—May, 2005

cannot be distinguished. The gas is distributedthroughout the small and large bowel where a little fluidis present resulting in sharp bowel-air interfaces whichappear as multiple closely apposed rounded orpolyhedral structures on plain radiograph.2 The preciselevel of obstruction may be evident in high GI obstructionbut is difficult to determine in a low gut obstruction. HighGI obstruction occurs most commonly at the level ofduodenum and proximal jejunum and plain radiographyalone is often diagnostic.

Bilious vomiting indicates obstruction distal to theampulla of Vater. Although there is little role of contrastexamintion in high gut obstruction,5 GI contrastexamination should be performed in obstructionspresenting beyond first few days of life to rule outmalrotation and midgut volvulus. The stomach isemptied through a nasogastric tube before upper GIcontrast study is undertaken.

Barium suspension is not used in cases of suspectedperforation or if there is a risk of barium inspissations.Aspiration into lungs should be avoided while usingcontrast agents because commonly used high osmolalityionic contrast may produce severe pulmonary edema.Hypertonic water-soluble ionic contrast media may beuseful in relieving obstruction in meconium ileus bydrawing water into the bowel lumen. However, this maycause fluid and electrolyte imbalance. Therefore, infantshould be hydrated and serum electrolytes monitoredbefore the procedure. Non-ionic low osmolality contrastmedia are preferred in most circumstances. Barium ispreferred in cases of suspected Hirschsprung’s disease orother conditions where delayed films have diagnosticvalue.High Intestinal Obstruction: The usual presentation isvomiting which may be bile stained if obstruction is distalto ampulla of Vater. The plain radiograph is oftendiagnostic and further radiological evaluation may beunnecessary. However, an upper gastrointestinal seriesmust be performed in all patients with incompleteintestinal obstruction. The causes of high obstructioninclude pyloric atresia, duodenal atresia, malrotation withmidgut volvulus or Ladd’s bands and proximal jejunalatresia.2 Partial obstruction results from jejunal stenosis,peritoneal bands, duplication cyst, malrotation andMeckel’s diverticulum.4

Low Intestinal Obstruction: Failure to pass meconium inthe first 24-48 hours of life may be due to structural orfunctional reasons. The causes include ileal or colonatresia, Anorectal malformations, Hirschsprung’s disease,meconium plug syndrome, and neonatal small left colonsyndrome.

Ultrasonography (US) is often the first modality to beused in investigation of child with abdominal lump orsuspected hypertrophic pyloric stenosis. US is highlyaccurate in the diagnosis of hypertrophic pyloric stenosisand extremely useful in the investigation of mass lesionssuch as enteric duplication cysts and mesenteric or

omental cysts.1

US is the modality of choice for prenatal screening, butoccasionally additional imaging information is needed.6

MRI is being increasingly used for prenatal imaging ofcongenital anomalies. The use of fast sequences like singleshot fast spin echo and echoplanar imaging has enabledsuccessful prenatal MR imaging. Esophageal, duodenal,or small bowel atresia can be diagnosed on antenatal MRI.On MRI, the signal intensity differences of the dilatedbowel may provide additional information comple-mentary to the US in identifying the site of obstruction.The proximal small bowel (fluid content) appearshyperintense on single-shot fast spin echo (SSFSE) andhypointense on T1-weighted fast spin echo (FSE)imaging. In contrast, the distal small bowel and colonappear hypointense on SSFSE and hyperintense on T1-weighted FSE imaging due to presence of meconium.7,8

ESOPHAGUS

Esophageal Atresia (EA) and Tracheo-Esophagealfistula (TEF)

The presence of polyhydramnios, reduced intraluminalliquid in the fetal gut and inability to detect the fetalstomach on prenatal ultrasound may provide an earlyclue to the possibility of esophageal atresia.9

The chest radiographs (AP and Lateral) demonstrateproximal esophageal pouch filled with air. The abdomenis always included in the radiograph to look for air in thegastrointestinal tract. The absence of gas in stomach orintestinal tract is suggestive of pure esophageal atresia(EA) without fistula or EA with proximal tracheo-esophageal fistula. The position of aortic arch should beconveyed to the surgeon as it may help determine thesurgical approach. When plain radiographs fail toindicate the side of the arch, and as a preoperative work-up, echocardiography should be performed beforesurgery to prognosticate and plan successful outcome.10

Chest radiograph may show consolidation due toaspiration pneumonia especially in the dependant upperlobes in supine position.

Radiographically, there is inability to pass a red rubbercatheter into the stomach. The proximal pouch may beoutlined due to swallowed air (Fig 1a). Gentle injection ofair via the tube may distend the proximal pouch. Thedistance between proximal and distal esophageal pouchcan be assessed only after a gastrostomy in a stagedprocedure. Isolated long gap esophageal atresia is knownto be associated with 13 pair of ribs.12

The diagnosis is frequently delayed in H-type fistula.The fistula is more precisely termed as N-type fistula as itcourses obliquely from the esophagus upwards to thetrachea (Fig 1b). Most H-fistulas are at thoracic inlet (T2-3). Tube esophagogram under fluoroscopic guidance withpatient in the lateral or steep prone oblique position is thebest way to demonstrate H-type fistula. The nasogastrictube placed at GE junction is gradually withdrawn while

Imaging of Congenital Anomalies of the Gastrointestinal Tract


up radiographs may be obtained if initial findings aresuspicious.

Associated anomalies are frequently seen in suchindividuals including features of the VACTREL spectrum(vertebral anomalies, anorectal malformation,cardiovascular malformation, tracheo-esophageal fistulawith esophageal atresia, renal anomalies and limbdefects). The other recognized associations are trisomy 18,trisomy 21, CHARGE syndrome, Potter syndrome andpresence of 13 pair of ribs.3,15

The dilatation of upper pouch may persist for monthsfollowing repair of atresia. Patients with repairedesophageal atresia show a high incidence of abnormalperistalsis in the esophagus, which may causedysphagia.3,16 Anastomotic strictures and gastro-esophageal reflux occur commonly after EA and TEFrepair. The incidence of stricture increases in patients withlong gap EA with a delayed primary repair17 and reflux.

STOMACH

Gastric Atresia, Antro-pyloric Membranes: Congenitalgastric obstruction is rare. Isolated pyloric atresia,pyloric/ prepyloric membrane, or antral webs areuncommon causes of gastric obstruction in the newborn.Pyloric atresia is classified into three types: (a) completeatresia with no connection between the stomach andduodenum, (b) complete atresia with a fibrous band

injecting contrast at various levels.10 A small amount ofisotonic non-ionic contrast medium or properly dilutedbarium should be used. The contrast should be aspiratedback immediately after the study.

Esophageal stenosis and webs may be associated withtracheoesophageal fistula.13,14 Up to one quarter of patientswith EA & TEF have associated with GI anomaliesincluding pyloric stenosis, duodenal/small bowel atresia,anorectal malformations. There should be high index ofsuspicion for associated anomalies. The pattern of airdistribution on plain radiographs may provide clue tothese anomalies. Air confined to the stomach and orduodenum suggests associated duodenal atresia. Follow

Fig 1a. Oesophageal Atresia with distal Tracheosophageal fistula.Lateral radiograph shows air filled dilated proximaloesophageal pouch. The presence of air in the stomach andthe bowel indicate distal tracheosophageal fistula.

Fig 1b. H-type tracheoesophageal fistula. The contrast studydemonstrates the superiorly angulated fistula (arrow) fromthe oesophagus to the trachea.



connecting the stomach and duodenum, (c) and a gastricmembrane or diaphragm.18,19 The congenital antro-pyloricwebs can be diagnosed on UGI contrast study wherethey are seen as linear defects resulting in ‘ pseudo doublebulb’ appearance, as the inflowing barium outlines thespace between the antrum and pylorus first and then theduodenal bulb.20 The membrane may be detected onsonography if the stomach is filled with clear fluid.

Congenital Hypertrophic Pyloric Stenosis (CHPS):

CHPS is characterized by hypertrophy of the circularmuscles. Recent work suggests that impaired neuronalnitric oxide synthase synthesis in the myenteric plexus isan important contributing factor in the pathogenesis ofinfantile hypertrophic pyloric stenosis as well as ofachalasia, diabetic gastroparesis, Hirschsprung’s disease,and Chaga’s disease.21 The mainstay of diagnosis remainspalpation of the hypertrophied pylorus in a quietlyfeeding baby. Ultrasonography is the primary imagingmethod, if required, and has replaced contrast evaluation.There is controversy over exact measurements of thegastric outlet in normal and hypertrophic pylorus. Thethickness of the muscle is the most discriminating andaccurate criterion for the diagnosis of hypertrophicpyloric stenosis.22

Ultrasonographically the antro-pyloric muscle of eachpatient is measured in the midlongitudinal plane (Fig 2a).The stomach is usually well distended allowing easyidentification of the antro-pyloric region. The water orglucose solution may be given in cases of inadequatedistention but should be removed after examination toprevent vomiting and aspiration. The antro-pyloricmuscle less than 2 mm thick should be consideredunequivocally normal.23 The muscle thickness of 3 mm ormore is abnormal (Fig 2b) and diagnostic for pyloricstenosis, whereas muscle thickness from 2mm to less than3 mm is abnormal but not specifically diagnostic forpyloric stenosis.24 The sonographic measurements in

pylorospasm may overlap those accepted as positive forhypertrophic pyloric stenosis. In pylorospasm, there isconsiderable variability in measurement or imageappearance with time during the study.24 This is animportant clue for diagnosing pylorospasm. Thesonographic double-track sign can be seen in cases ofpylorospasm as well as hypertrophic pyloric stenosis. It isnot pathognomonic for hypertrophic pyloric stenosis.25

A barium study may be performed if ultrasound isinconclusive or if gastro-oesophageal reflux is suspected(Fig 2c). The hypertrophied muscle mass causeselongation and narrowing of pyloric canal (‘string sign’)as well as a bulge in the distal antrum with streak of

Fig 2a. Hypertrophic pyloric stenosis (HPS): Longitudinal view onsonography shows elongated pyloric canal with thickenedhypoechoeic muscle (arrow).

Fig 2b. Hypertrophic pyloric stenosis (HPS): On tranverse view,hypertrophied pylorus has a doughnut appearance. Themucosa is echogenic with surrounding hypoechoic musclelayer (between cursors).

Fig 2c. Hypertrophic pyloric stenosis (HPS): Upper GI barium studyshows narrowed and elongated pyloric canal. Thehypertrophied muscle mass produces indentation on theduodenal cap and the antrum.



barium pointing towards pyloric channel (‘beak sign’).The barium may outline crowded mucosal folds asparallel lines (‘double/triple track sign’). These findings,if transient, should be interpreted with caution. Theimportance of clinical examination and test feed isemphasized especially in cases with equivocalsonographic or barium findings. This will reduce the riskof false-positive diagnoses and negative laparotomies.26

DUODENUM

Duodenal Atresia/StenosesComplete duodenal obstruction is much more commonthan congenital gastric obstruction. Vomiting is usuallybilious as obstruction is often distal to the ampulla ofVater. The plain radiograph of the abdomen shows‘double bubble’ sign corresponding to air in stomach anddilated proximal duodenum with absence of air in distalgastrointestinal tract. This condition may be diagnosedwith antenatal ultrasound showing fluid filled double-bubble and polyhydramnios. Fetal karyotype should beobtained as up to 30% of patients have Down’ssyndrome.9 There is a frequent association with otheranomalies in up to 50% of cases. Partial duodenalobstruction is caused by annular pancreas, Ladd’s bands,midgut volvulus, pre-duodenal portal vein andduplication cyst.

A pre-duodenal portal vein (persistent left vitellinevein) results from normal situs asymmetry, and iscommonly found in patients with heterotaxy. Theresultant portal vein courses anterior to the pancreas andduodenum. The diagnosis is made by identifying theprepancreatic course of the portal vein on sonography, CTor MR imaging. It is now believed that in most cases ofduodenal obstruction associated with preduodenal portalvein, the obstruction is due to a primary, obstructingduodenal lesion such as intraluminal membrane or weband such a lesion should be suspected in these patients ifduodenal obstruction is present. 2, 27

SMALL BOWEL

Jejunal/ileal atresia

Intestinal atresias account for about one third of all casesof neonatal intestinal obstruction. Prenatalultrasonography is more reliable in detection of duodenalatresia than the more distal lesions. The survival rate hasimproved significantly in most of the series with theoperative mortality being less than 1%. More distal theatresia better is the survival. An increased mortality isobserved in multiple atresias, ‘apple peel’ syndrome, andwhen atresia is associated with meconium ileus,meconium peritonitis and gastroschisis.28 Intestinal atresiaoccurs in approximately 10% to 20% of neonates withgastroschisis and may be missed at the initial closure if athick ‘peel’ obscures the bowel.29

Jejuno-ileal atresia results from vascular occlusion andischemic injury to the developing gut. Jejuno-ileal atresiais classified into four types. Type I is a simple intraluminaldiaphragm composed of mucosal and submucosalelements. No interruption of the muscularis is present.Type II represents an atresia with solid fibrous cord (allthe layers of intestinal wall interrupted) connecting theblind ends of the bowel. Type III is an atresia withcomplete separation of the blind ends and an associatedmesenteric defect. The familial form of multiple atresias isconsidered as Type IV.10, 30

The disproportionate dilatation of the bowelimmediately proximal to the atresia results in a bulbouscontour suggestive of congenital small bowelobstruction.31 Plain radiography is usually diagnostic andfurther radiological evaluation (upper GI series) is notnecessary (Fig. 3). In cases of partial obstruction littleamount of distal gas is usually present. A small amount ofair may be injected through a nasogastric tube to confirmcomplete or partial jejunal obstruction. In isolatedproximal atresia of the duodenum or jejunum, the colonis of normal size because the remaining bowel distal tothe atresia produces sufficient intestinal secretions toproduce a normal caliber colon.4 In ileal atresia, the colonhas a normal location but the caliber is reduced(functional microcolon) 32. In low intestinal obstructioncontrast enema should be done to exclude colonic lesion,meconium ileus or Hirschsprung’s disease especially

Fig 3. Small bowel atresia: Plain radiograph demonstrates multipledilated bowel loops and fluid levels. Peritoneal calcificationsare seen as a result of meconium peritonitis.



when dilated small bowel or colon cannot bedifferentiated on plain radiography.4, 10 Sonography maybe useful in differentiating meconium ileus and ilealatresia. In meconium ileus, the dilated bowel loops arefilled with echogenic material, whereas in ileal atresia thebowel contents are echo-poor.33

The ‘apple peel’ syndrome is thought to followintrauterine occlusion of the distal superior mesentericartery (SMA) resulting in a proximal jejunal atresia withabsence of mid-small bowel and the dorsal mesentery.The distal bowel derives its blood supply from theproximal SMA. The distal small bowel spirals around itssingle vascular supply and resembles an “apple peel.”34, 35

Intestinal stenoses are much less common thanintestinal atresias. Stenoses result from three majorcauses: external compression of the bowel lumen,intramural narrowing resulting from rests of heterotopictissue, and incompletely perforated intraluninal webs.10

Stenoses caused by extrinsic impression on the bowellumen are almost entirely confined to the duodenum asa result of annular pancreas36 or peritoneal bands.

Malrotation

In the fetal life, the primitive midgut herniates into theextraembryonic celom and later returns into theabdominal cavity between 6-10 weeks. During thisprocess, the primitive midgut rotates anticlockwisethrough 270 degrees around the axis of the superiormesenteric artery. Both, duodeno-jejunal junction andcaecal pole undergo 270 degree anti-clockwise rotationfollowed by fixation of duodeno-jejunal junction in theleft upper quadrant and the ileo-caecal junction in theright lower quadrant. Interruption of this process at anypoint results in a narrow base of small bowel mesenterywith predisposition to volvulus.2 The term ‘malrotation’or ‘Nonrotation’ is a misnomer as it results from lack ofcomplete intestinal rotation The Ladd’s bands orhyperfixation bands can form due to faulty peritonealattachments as a result of malfixation and malrotation ofthe intestine. Rotational abnormalities are seen inapproximately 70% of patients with situs ambiguous(heterotaxy).

A neonate with bilious vomiting on the first day of lifeand radiographic evidence of complete duodenalobstruction does not require further radiologicalevaluation. On the other hand a neonate with biliousvomiting who has been normal for first few days or withradiographic evidence of incomplete obstruction(presence of gas in distal part of gut) requires furtherevaluation.4 An upper gastrointestinal series is usuallyperformed initially to demonstrate the level and nature ofobstruction. On a supine radiograph the normal C- loopcrosses the midline and duodeno-jejunal junction lies tothe left of the left vertebral pedicles at the level of theduodenal bulb. The normal duodeno-jejunal junction maybe mobile and easily displaceable in infancy, especially inchildren less than 4 months of age.37

Any duodenal obstruction that occurs after immediatepostnatal period should be assumed to be midgutvolvulus until proved otherwise.38 The upper gastro-intestinal examination shows a typical corkscrew appea-rance of the duodenum and proximal jejunum (Fig 4). Thedistal jejunum lies to the right of midline. The Ladd’sbands result in Z-shaped duodeno-jejunal configurationand usually obstruct at the third portion of the duodenumbut can obstruct more distally.39 A barium meal should bedone for suspected malrotation since a normal bariumenema does not exclude malrotation. The position ofcaecum may be normal in a significant number of patientswith malrotation.20 The UGI examination remains thegold standard for the diagnosis of malrotation

Fig 4. Midgut volvulus: Upper GI barium study demonstrates theclassic ‘corkscrew’ appearance of the duodenum andproximal jejunum.

Superior mesenteric vein (SMV) normally lies to theright of superior mesenteric artery (SMA). Malrotationmay be suggested on US if the SMV is to the left oranterior to the artery. However, this is neither a sensitivenor a specific sign. The sonographic “whirlpool sign” isobjective and a definite sign as volvulus, is shown at colorDoppler US as clockwise spiraling of the mesentery andSMV around the SMA.40, 41 Recent literature is replete withmany diagnostic criteria for various imaging modalities.The multiplicity of the findings is a testimony to theunsatisfactory nature of their yield.

Meconium peritonitis

Meconium peritonitis results from an in-utero bowelperforation proximal to a complete obstruction. Althoughcommonly associated with bowel atresias, it may bepresent in asymptomatic neonates with in-utero sealedbowel perforation. Plain abdominal radiograph may



show peritoneal calcifications due to calcified meconium(Fig 5). The small bowel loops may be dilated in cases ofassociated bowel atreasia. These calcific densities may beseen in the scrotum also if the processus vaginalis ispatent. On ultrasound, the calcifications are seen asechogenic densities outside the bowel wall.

length of the gut where they lie along the mesentericborder and share a common muscle wall and bloodsupply. The duplications commonly occur in the distalileum (Fig 7) and esophagus. Duplication cysts are usuallyspherical lesions and less often tubular. Thecommunication with the adjacent bowel is uncommon inspherical lesions and is more likely to occur with tubularduplications.43

Meconium ileus

Meconium ileus is a low intestinal obstruction caused byinspissated meconium usually in the terminal ileum andis almost always associated with cystic fibrosis. The plainabdominal radiograph usually shows low small bowelobstruction with dilated small bowel loops but absent orscant fluid levels. Although the absence of air-fluid levelsstrongly suggests meconium ileus, the presence of airfluid levels does not exclude it as some cases dodemonstrate air-fluid levels, especially those withassociated complications such as volvulus and stenosis oratresia.18,42 Volvulus of a meconium laden heavy bowelloop is common and can lead to intestinal stenoses,atresias, gangrene and perforation. The “soap bubble”appearance caused by admixture of air and meconium isfrequently seen (Fig 6). It can, however, also be seen withileal atresia, colon atresia, Hirschsprung’s disease and themeconium plug syndrome.18 Calcifications or pseudocystmay be seen due to meconium peritonitis and localizedascitis

Enteric Duplication Cyst

Enteric duplication cysts can occur anywhere along the

Fig 5. Meconium ileus: plain radiograph shows multiple dilatedbowel loops (low intestinal obstruction) and ‘soap bubble’appearance in the right lower quadrant.

Fig 6. Sonogram of a distal ileal duplication cyst. An anechoiclesion with typical wall characteristics is seen-innerechogenic mucosal stripe and outer hypoechoic muscle layer(arrow).

Ultrasound is the imaging modality of choice for theevaluation of an abdominal mass in the neonate. The mostcommon clinical manifestation of intra-abdominal entericduplication cysts is intestinal obstruction. Occasionally,

Fig 7. Hirschsprung’s disease (recto-sigmoid): Contrast enema(lateral radiograph) shows abnormal rectosigmoid index andtransition zone with narrow caliber of the rectosigmoid anddilated proximal ganglionated sigmoid colon. The extensiveulcerations are due to enterocolitis.



haemorrhage or gastrointestinal bleeding may occur dueto ectopic gastric mucosa which is seen in 10-20% of caseswhich makes it visible with technetium-99mpertechnetate scanning and may be of diagnostic value.

The cyst shows the echogenic inner rim of mucosa andhypoechoic outer rim of the muscle layer (double wallsign). This is most easily identified in the dependentportion of the cyst.44 Peristalsis of the cyst wall whenvisible, is another useful sign.45 The cyst is fluid filled,usually unilocular and anechoic. Occasionally, internalechoes and septations may be seen due to hemorrhage orinspissated mucoid material. Rarely, the cyst iscompletely echogenic and gives false impression of asolid lesion. Multiple duplication cysts may be present in15-20% of cases.46

Esophageal duplication cyst: duplications of theesophagus are the second most common duplication ofthe gastrointestinal tract after ileal duplications.43,47 Anesophageal duplication cyst may present with pressuresymptoms such as dysphagea, stridor, or breathingdifficulty. On chest radiograph, duplication cyst is seen asposterior mediastinal mass. Ultrasound may demonstratedouble-layered wall especially in large cysts abuttingposterior chest wall. CT and MRI demonstrate welldelineated outlines with non-enhancing attenuationvalues of water. Endoscopic US can accurately diagnoseduplication cyst by demonstrating contiguity of themuscularis propria of the esophagus with the musclelayer of the cyst wall.48

Duodenal duplication cyst is a rare congenital anomalyand usually presents with symptoms of obstruction, butmay cause biliary obstruction and pancreatitis. 49 Thedifferential diagnosis of duodenal duplication includes acholedochocele, a pancreatic pseudocyst and intraluminaldiverticulum.50

Mesenteric Cyst (Lymphangioma)

Mesenteric cyst is a congenital malformation arising dueto sequestration of lymphatic vessels.51 These are usuallyseen in the mesentery and less often in omentum andretroperitoneum. Children usually present in the firstdecade, with increasing abdominal girth or a palpableabdominal mass. Sonography reveals a thin-walledunilocular or multilocular cystic lesion, whereas CT andMRI demonstrate variable characteristics of the cystcontents (usually water-to fat) depending upon whetherfluid is chylous, infected or haemorrhagic. Ultrasound isparticularly useful to demonstrate the thin septationswhich may not be well seen on CT. Rarely, a mesentericlymphangioma may contain calcification mimicking amesenteric teratoma. 52

LARGE BOWEL

Colonic Obstruction

Colonic atresia is quite rare and often indistinguishable

from obstruction of the distal ileum. The right colon ismost commonly affected.53 Plain radiographdemonstrates features of a low intestinal obstruction withair-fluid levels or mottled pattern due to retainedmeconium. Contrast enema shows a distal microcolonand complete obstruction at the level of atresia. On US,dilatation of the distal small bowel and proximal colonwith echogenic contents due to retained meconium maybe seen.4

Hirschsprung’s Disease

Approximately one-fifth of neonatal intestinalobstructions are due to Hirschsprung’s disease.2 In aboutthree quarters of these cases, the area of aganglionosis islimited to the rectum and sigmoid (short segmentdisease).54 Long segment disease involves a variableportion of the colon proximal to the sigmoid and in totalaganglionosis coli the entire colon and a part of theterminal ileum20 is involved. Total colonic aganglionosisand ‘ultra short segment’ disease is rare.

The majority of patients present within the first 6weeks in life. Neonates present with failure to passmeconium, abdominal distention, vomiting orenterocolitis. Enterocolitis is the leading cause of death inHirschsprung’s disease.55 Enterocolitis and perforation ismore common in the long segment disease. Theperforation occurs most commonly in the ascending colonor in the appendix.56, 57

Imaging Features: Plain radiograph shows features oflow bowel obstruction with colonic dilatation out ofproportion to the small bowel.58 There may be absence ofrectal gas or small amount of gas may be seen in rectum(especially on prone films) on plain radiograph. However,the absence of rectal gas is not specific for Hirschsprung’sdisease, being more commonly seen in infants with sepsisand necrotizing enterocolitis.59

Digital examination of the rectum or enemas,inpatients scheduled for barium studies should not be doneas it may distort the findings.10 For the same reason, thestudy (enema) is never performed with an inflated Foleycatheter in the rectum.10 Barium enema is performedcarefully on an unprepared patient by inserting a straight-tipped catheter to a point just beyond the anal sphincter.The patient should be placed in lateral position andbarium infused slowly as rapid infusion can distend andmask the transition zone. The contrast agent should beprepared with normal saline to avoid possibility of waterabsorption from the large surface area of dilated colon.3

The diagnostic feature in short segment disease is funnelshaped transition zone and reversal of the recto-sigmoidratio (Fig 7). Normally, the rectum is the most distensibleportion of the bowel and has a diameter greater than thatof the sigmoid colon (recto: sigmoid ratio >1).20 Theradiological transition zone is commonly found distal tothe pathological transition zone.60 There may be irregular,uncoordinated contractions in the aganglionic segment(20% of cases) which may be mistaken for mucosal



ulcerations. Delayed films after 24 hrs may demonstrateprolonged retention of barium in the sigmoid colon (notrectum which normally holds barium for 24 hours). Thisis a strong indicator of Hirschsprung’s disease, even whenthe enema findings have been inconclusive. Rectal biopsyis always necessary for confirmation.

The diagnosis of total colonic aganglionosis is muchmore difficult. The radiological findings viz.foreshortening, rounding of the colonic flexures and smallcaliber colon2 are relatively nonspecific. The prolongedretention of barium on delayed films should alert one tosuspect the diagnosis.61 Presence of skip lesions inHirschsprung’s disease is extremely rare (controversial ).Awareness of this variant aids in the interpretation of thebarium enema in children with signs and symptoms ofaganglionosis, especially when the rectal biopsy isnormal.62 The associations of Hirschsprung’s diseaseinclude Down’s syndrome, ileal and colon atresia andneuro-cristopathies.63-65

Anorectal Anomalies

The anorectal malformations are divided into high andlow types depending upon whether the termination ofhindgut is above or below the puborectalis sling.Anorectal anomalies are often associated with fistuloustracts opening into the genitourinary system. Althoughthe distinction between high and low lesions can be madeclinically, the radiologic study is required to evaluate theinternal anatomy. This is usually accomplished usingcontrast studies. In both male and female infants with lowlesions, there is usually a visible perineal opening and thecommunication with the genitourinary tract is absent10,20

However, there are cases with imperforate anus withexternal signs of a low lesion with demonstrable fistulainto the anterior urethra either at surgery or byradiographic studies.66 These cases should be consideredan intermediate form of imperforate anus with externalsigns of a low lesion but with fistula characteristically tothe membranous or bulbous urethra.65 High lesions aretreated with initial diverting colostomy and definitiverepair at a later age. A pressure augmented distalcolostogram is recommended prior to definitive repair,both to confirm the level of rectal atresia and to define anyassociated fistulous communication.67 Water- solublecontrast medium is injected under mild pressure througha Foley’s catheter with its balloon inflated to occlude thestoma. The fistulous tract not identified on theconventional contrast colostogram (Fig 8) may bedelineated when an augmented-pressure modification ofthe technique is utilized.66 Micturating cystourethro-graphy (MCU) and/or retrograde urethrography (RGU)are also useful to demonstrate fistula and presence ofvesicoureteric reflux.

The easily available plain radiograghy is simple and isoften the preliminary investigation to be used inevaluation of these patients. Prone cross table lateral viewwith babies kept in genu-pectoral position is useful in

determining the level of atresia.68 The use of invertogramis to be discouraged as it causes unnecessary stress.During invertogram, the baby usually keeps cryingcausing contraction of puborectalis sling and obliterationof the lower rectum. Also, the rectum may be pulled in thecephalic direction resulting in error of classification. Inthose anomalies, which are associated with fistulae withthe urinary or genital tract, the fistula becomes the highestpoint of rectum in an invertogram and gas may escaperesulting in less distension of the rectum. In proneposition, the fistula is lowest and therefore rectum isbetter distended causing adequate delineation of therectal gas 68. The pubococcygeal line and M line areimaginary lines used to represent the level of puborectalissling on lateral radiographs. The “M” line is a betteranatomic correlate of puborectalis sling. The “M” linepasses horizontally through the junction of the lower thirdand upper two thirds of the ischium.

Ultrasonography can assess the distance of the rectalpouch in relation to the perineal surface. A pouch perinealdistance of < 1.5 cm is indicative of low anomalies, whilea pouch that terminates above the base of the bladder(superior extent of urogenital diaphragm) is indicative ofa high lesion.69 However, the distinction between highand intermediate anomaly cannot be made out with thistechnique. Recently, anal endosonography has been usedas an accurate alternative to MRI in the assessment ofanorectal malformations after repair.70

CT and MRI are the modalities of choice to delineatepelvic anatomy including puborectalis muscle andexternal sphincter. Congenital anorectal malformationsare found in many forms, and are frequently associated

Fig 8. Lateral view of distal cologram shows rectourethral fistula ina male infant with a high anorectal malformation. Associatedsacral dysgenesis is seen.



with other anomalies, especially of the spine, spinal cord,and urogenital system.71 Magnetic resonance imaginghas proven to be the single stop modality to answer all thecrucial questions such as level and type of malformation,type of fistula, developmental state of the sphinctermuscle complex, and the presence of associatedanomalies.71-73 MRI has contributed to a better insight inthe morphology and pathogenesis of such complexcongenital malformations.71.

Spinal radiographs must be examined carefully forabnormalities, because spinal pathology has profoundeffect on the outcome. Normal radiographic andsonographic appearance of spinal anatomy in childrenwith anorectal malformation makes MRI superfluous, butif radiographs or ultrasound are uninformative/abnormal, MRI should be used to accurately depictpossible intraspinal pathology.74 Sonography of theurinary tract for associated renal anomalies is essential inall patients with anorectal malformation.

Megacystis-Microcolon-Intestinal HypoperistalsisSyndrome (Berdon Syndrome)75

This syndrome is a rare congenital cause of intestinalobstruction. The abdominal distention is due to dilatedbladder and dilated short bowel in absence of organicobstruction. There is hypomotility of small bowel withretrograde peristalsis on upper GI contrast study while anenema shows a microcolon. Ultrasound will show adilated bladder and bilateral hydrourteronephrosis. Theanterior abdominal wall musculature is thin, similar toprune belly syndrome.

Meconium Plug Syndrome

Immature left colon is a form of functional obstructionassociated with prematurity, maternal drug ingestion(magnesium preparations or high doses of sedatives),andin babies of diabetic mothers.4,76 The affected infantspresent with distal bowel obstruction and delayedmeconium passage. However, the bowel distention is lesssevere than with a mechanical obstruction. The contrastenema typically shows a mildly dilated right andtransverse colon and a small left colon with an abrupttransition at the level of splenic flexure. The meconiumplugs are seen as multiple elongated filling defects indilated colon. The contrast enema using water-solublecontrast media is both diagnostic as well as therapeutic. Ifclinical improvement does not follow over next few hoursor days, suction rectal biopsy is recommended to rule outHirschsprung’s disease.

CONCLUSION

The goal of imaging is to provide an accurate diagnosisand other relevant information to the clinician whileminimizing patient discomfort and radiation exposure.The judicious choice of various imaging modalitiesrequires a concerted effort of the clinician and the

radiologist aimed at providing best information and helpto the treating clinician to plan out the most suitabletreatment efficaciously.

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Hyperalgesia: Molecular Mechanism and Clinical ImplicationsI read the book “Hyperalgesia: Molecular Mechanism and Clinical Implications” with a great interest.

Pain is the terrible fear of mankind and it is more terrible than death itself. Pain relief is the most importanttask of a physician. There are various theory and treatment associated with acute and chronic pain, still chronicpain most of the time and in most of the world remain untreated, may be because of lack of understanding ofits etiology and mechanism. Before treating pain at each level it is important to understand mechanism of actionat peripheral and central level.

This book consists of 26 contributions submitted by renowned researchers from different parts of the world.The book is divided into five sections, the first section discusses the basic question and defined very well abouthyper excitability. This section also gives very good insight about which nomenclature should be used in variousconditions of pain.

Second section describes the exiting new developments in molecular research and common pathwayemerging to understand peripheral mechanism of hyperalgesia like discovery of the capsaicin receptor on theunderstanding of peripheral sensitization, contribution of tetrodotoxin-resistant sodium channels indevelopment of peripheral hyperalgesia, VR-1 receptors or TRPV1 receptors is a key substrate in hyperalgesia.

Third section describes transudation mechanism of nociceptors following the pathological process. Forexample, mechanism of cold hyperalgesia induced by inflammatory process, visceral pain and hyperalgesia,ASIC3 is responsible for development of mechanical hyperalgesia following muscle injury. This section alsoexplains why it is difficult to adequately treat pain in cancer patients.

The fourth section describes the role of central nervous system in hyperalgesia and explains very well themolecular mechanism of central hyperalgesia and its neurobiological features.

The fifth section explains that many brain specific functions also contribute to hyperalgesia and painchronicity.

It is a good reference book for clinician and basic scientist working in the area of molecular biology,neurobiology, molecular pharmacology.

It is also a good reference book for people working in the area of genetics and trying to find out the cause ofpain at genetic level. In addition, it is a useful reference book for pharmaceutical industries involved in makinganalgesic/and doing pain research.

For general practitioner and clinician it may be of limited use as the main emphasis is on molecular aspectof pain and its mechnism.

Dr. Sushma Bhatnagar,Associate Professor,

Unit of AnaesthesiologyDr BRAIRCH, AIIMS,

New Delhi.

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