Correct answer: B . Absence of ganglion cells on rectal biopsy.
Rationale
Hirschsprung's disease occurs in approximately 1 out of 5,000 live births and is caused by absence of ganglion cells in the myenteric plexus of the intestine. The condition arises from failure of the neural crest cells to fully migrate caudally along the intestine during early gestation, resulting in a distal portion of the intestine being aganglionic. Rectal and distal sigmoid involvement is seen in around 85% of cases, with the other 15 percent involving more proximal intestine. It can rarely involve the entire colon and small intestine. Ganglion cells inhibit local smooth muscles, resulting in the characteristic inability for aganglionic bowel to relax. This lack of inhibition gives rise to the absence of rectoanal inhibitory reflex (RAIRs) during anorectal manometry. The lack of inhibition also produces a transition zone on contrast enema, with the distal aganglionic bowel being narrow and the more proximal bowel containing ganglia being dilated. Lack of meconium passage in the first 48 hours of life raises concern for Hirschsprung's disease. Other causes for possible failure to pass meconium include cystic fibrosis, anorectal malformation, small left colon syndrome, meconium plug syndrome and megacystis-microcolon-intestinal hypoperistalsis syndrome.
References
Kenny, S et al. Semin Pediatr Surg. 2010 Aug;19(3):194-200.
Wyllie R et al. Pediatric Gastrointestinal and Liver Disease. 4th edition. Elsevier Saunders, Philadelphia, 2011.
