13.4 Hirschsprung Disease & Biliary Atresia

Hirschsprung Disease

Hirschsprung disease (HD) is a congenital motility disorder caused by failure of neural crest cells to migrate completely into the distal hindgut during gestation, leaving a segment of bowel without ganglion cells in the submucosal (Meissner) and myenteric (Auerbach) plexuses. The aganglionic segment cannot relax, so it remains tonically contracted and functionally obstructs the passage of stool; the disease is always described by the extent of aganglionosis starting at the anus and extending proximally, most commonly confined to the rectosigmoid colon (short-segment disease, roughly 80% of cases). HD is more common in males, occurs in approximately 1 in 5,000 live births, and is associated with Down syndrome (trisomy 21) and other neurocristopathies such as multiple endocrine neoplasia type 2.

Presentation

The single most testable historical clue is failure to pass meconium within the first 48 hours of life in a term infant, a finding present in the large majority of HD cases and one that should always trigger consideration of HD rather than being dismissed. Affected neonates go on to develop progressive abdominal distention and bilious vomiting. On digital rectal exam, withdrawal of the examining finger is often followed by an explosive release of gas and stool, sometimes called the "squirt sign," as the obstruction is transiently decompressed — a classic bedside finding. Children with shorter aganglionic segments may present later in infancy or even childhood with chronic constipation, abdominal distention, and failure to thrive rather than a neonatal emergency, which broadens the differential with functional constipation; red flags favoring HD over functional constipation include onset from birth, failure to thrive, and an empty rectal vault despite a distended abdomen.

The most feared complication is Hirschsprung-associated enterocolitis (HAEC), which can occur before or after surgical correction and presents with fever, marked abdominal distention, explosive or foul-smelling diarrhea, and rapid progression to sepsis and shock if untreated; management requires rectal irrigation, bowel decompression, IV fluids, and broad-spectrum antibiotics.

Diagnosis and Treatment

Rectal suction biopsy is the gold-standard diagnostic test: histology demonstrates the absence of ganglion cells in the submucosal plexus along with hypertrophied nerve trunks, and acetylcholinesterase histochemical staining shows increased, coarse acetylcholinesterase-positive fibers in the lamina propria, confirming the diagnosis when ganglion cells are absent. A contrast (barium) enema may show a transition zone — a caliber change between the narrow aganglionic distal segment and the dilated, normally innervated proximal bowel — but this zone can be subtle or absent in neonates because the proximal bowel has not yet had time to dilate, so a normal-appearing enema does not exclude HD and biopsy remains definitive.

Definitive treatment is surgical: a pull-through procedure, which resects the aganglionic segment and brings normally innervated, ganglionic bowel down to the anus, performed once the transition to normal ganglionic bowel is confirmed intraoperatively or by pathology, often after an initial period of decompression via rectal irrigations or, in some cases, a temporary colostomy.

Biliary Atresia and Neonatal Cholestasis

Biliary atresia (BA) is a progressive, fibro-obliterative process destroying the extrahepatic, and eventually intrahepatic, bile ducts, causing complete obstruction to bile flow. It is the single most common indication for pediatric liver transplantation and, if untreated, progresses to biliary cirrhosis and liver failure within the first two years of life.

The defining clinical feature is conjugated (direct) hyperbilirubinemia — jaundice that persists beyond the first 2 weeks of life (3 weeks in breastfed infants by some criteria) accompanied by pale, acholic stools and dark urine, reflecting failure of bilirubin to reach the gut. Hepatomegaly develops as obstruction progresses. The single highest-yield exam rule in this domain: any infant with jaundice persisting beyond 2 weeks of age must have a conjugated (direct) bilirubin fraction measured — jaundice should never be attributed to breast milk jaundice or physiologic jaundice without first excluding a conjugated hyperbilirubinemia, because early diagnosis of BA is time-critical.

Workup

Once conjugated hyperbilirubinemia is confirmed (generally direct bilirubin above 1 mg/dL if total bilirubin is below 5 mg/dL, or above 20% of total if higher), evaluation proceeds urgently:

The differential for conjugated hyperbilirubinemia in a neonate also includes choledochal cyst, neonatal (idiopathic) hepatitis, alpha-1 antitrypsin deficiency, TORCH infections, and metabolic or genetic cholestatic syndromes, all of which the workup above is designed to exclude.

Treatment

Definitive treatment is the Kasai portoenterostomy, in which the fibrotic extrahepatic biliary remnant is excised and a loop of jejunum is anastomosed directly to the porta hepatis to restore bile drainage from residual microscopic ductules. Outcomes are strongly time-dependent: success in achieving bile flow and clearing jaundice is substantially higher when the Kasai is performed before approximately 45-60 days of life, and outcomes decline with older age at surgery. This urgency is why the "jaundice beyond 2 weeks means check conjugated bilirubin" rule exists — every week of delay in recognizing BA is a week closer to a Kasai performed too late to succeed. Even after a successful Kasai, many children eventually develop progressive fibrosis and require liver transplantation, but a well-timed Kasai delays that need, often by years.