Hirschsprung Disease

Hirschsprung disease is a congenital disorder of intestinal innervation. Ganglion cells are absent from the myenteric (Auerbach) and submucosal (Meissner) plexuses of a variable segment of distal bowel, extending proximally from the anus for a variable distance.

The aganglionic segment fails to relax and permit normal peristaltic propulsion, producing functional obstruction. It is an important, common cause of neonatal and infant bowel obstruction.

Consider the diagnosis proactively in any infant with delayed passage of meconium beyond the first forty-eight hours of life. Prompt recognition and treatment help prevent the serious, potentially life-threatening complication of Hirschsprung-associated enterocolitis.

Pathophysiology and classification

• Failure of normal craniocaudal migration of neural crest cells during fetal development leaves the affected distal bowel without ganglion cells. The aganglionic segment invariably includes the rectum and extends proximally for a variable distance.
• The extent of aganglionosis classifies the condition. Short-segment disease is the commonest presentation and accounts for the substantial majority of cases. It is confined to the rectosigmoid region.
• Long-segment disease extends more proximally, involving a greater length of colon.
• In a small proportion of cases there is total colonic aganglionosis, involving the entire colon. In the rarest, most extensive cases it extends into the small bowel.
• The aganglionic segment remains persistently, tonically contracted. It fails to relax in response to an advancing bolus of bowel contents, producing a functional obstruction at this point.
• The normally innervated bowel proximal to the affected segment dilates. This accounts for the characteristic radiological appearance and the traditional, though somewhat imprecise, descriptive term "congenital megacolon".
• There is a recognised genetic association. A substantial proportion of cases involve mutations in the RET proto-oncogene. Incidence is well established as increased in children with Down syndrome and certain other genetic syndromes, so consider broader syndromic assessment in confirmed cases.

• Delayed passage of meconium beyond the first forty-eight hours of life is the classical early presenting feature in the neonatal period. Consider Hirschsprung disease in any infant with this pattern, as the great majority of healthy, term infants pass meconium within the first twenty-four hours of life.
• Where the diagnosis is not identified from delayed meconium passage alone, the neonatal presentation evolves. It is characterised by progressive abdominal distension, bilious vomiting from the developing functional obstruction, and difficulty with feeding. Severity and rate of progression vary with the extent of the aganglionic segment.
• A subset of children, particularly those with a shorter segment of aganglionosis, present later in infancy or childhood. The history is of severe, progressive constipation, often refractory to standard laxative treatment, with faltering growth and progressive abdominal distension.
• Consider the diagnosis in any child with unusually severe, treatment-refractory constipation, particularly with onset from early infancy. This distinguishes it from the far more common, generally more straightforward functional constipation.
• Digital rectal examination classically shows a tight, narrow anal canal and an empty rectal vault, as the functional obstruction prevents stool accumulating in the rectum.
• Withdrawal of the examining finger is characteristically followed by an often dramatic explosive release of gas and liquid stool, from sudden decompression of the obstructed, distended proximal bowel. This is a useful clinical sign supporting the diagnosis.
• Hirschsprung-associated enterocolitis is a serious, potentially life-threatening complication. It can occur both before and after definitive surgical treatment. It presents with fever, abdominal distension, explosive diarrhoea and, in severe cases, signs of sepsis and systemic illness.
• It needs urgent recognition and treatment, given the substantial morbidity and mortality risk if not promptly addressed.

• Rectal biopsy is the definitive, essential diagnostic investigation. Histological and histochemical examination shows absence of ganglion cells, hypertrophied nerve fibres and increased acetylcholinesterase staining.
• Suction rectal biopsy is generally the initial approach. It is relatively straightforward and minimally invasive, and suitable for neonates and young infants without general anaesthesia.
• Contrast enema does not give definitive histological confirmation, but supports the diagnosis and shows the likely extent of the aganglionic segment. It classically shows a transition zone between the narrowed, aganglionic distal segment and the dilated, normally innervated proximal bowel, with delayed contrast evacuation on subsequent imaging. It informs diagnostic support and surgical planning.
• In neonates the transition zone may not be clearly apparent, because there has been insufficient time for the characteristic proximal dilation to develop. A normal or non-diagnostic contrast enema in a neonate therefore does not reliably exclude the diagnosis.
• Anorectal manometry is a further, useful adjunct. It assesses the rectoanal inhibitory reflex, which is relaxation of the internal anal sphincter in response to rectal distension. The reflex is characteristically absent in Hirschsprung disease because of the underlying aganglionosis.
• The test is more readily and reliably performed in older children than in the youngest infants.
• Any neonate with delayed meconium passage beyond forty-eight hours, or any child with unusually severe, treatment-refractory chronic constipation from early infancy, warrants proactive consideration of this diagnosis and referral for specific diagnostic evaluation.

• Initial management of a neonate with suspected or confirmed Hirschsprung disease and significant bowel obstruction is bowel decompression. This is typically achieved through rectal irrigation: regular, gentle instillation and drainage of saline via a rectal tube, which helps decompress the distended, obstructed proximal bowel and reduces the risk of enterocolitis.
• Add nasogastric decompression and intravenous fluid support where clinically indicated by the severity of the presentation.
• Definitive surgical treatment is a pull-through procedure. The aganglionic segment is resected and the normally innervated, healthy proximal bowel is anastomosed to the anus.
• Several techniques are described, including the Swenson, Duhamel and Soave procedures, each differing in the technical approach to resection and anastomosis. The technique is selected according to surgeon experience, preference and patient factors.
• The procedure is increasingly performed via a minimally invasive, transanal approach in appropriately selected cases, avoiding formal laparotomy.
• Timing of definitive surgery is individualised to the clinical presentation and the infant's overall status.
• Some centres favour early, primary pull-through in the neonatal period, once the diagnosis is confirmed and the infant is otherwise stable.
• Others favour an initial period of bowel decompression, followed by staged definitive correction once the child has grown and decompression has been established. This may include a temporary diverting colostomy in more complex cases, particularly long-segment or total colonic disease, or where enterocolitis has occurred.
• Hirschsprung-associated enterocolitis, whether before or after definitive correction, needs urgent, aggressive management. It comprises bowel decompression (rectal irrigation), intravenous fluid resuscitation and broad-spectrum antibiotic therapy, given in time because of the substantial associated morbidity and mortality risk.
• Long-term follow up after definitive correction addresses ongoing bowel function. A proportion of children have persistent bowel dysfunction, including continued constipation or in some cases faecal incontinence, despite technically successful surgery, and need structured bowel management support.
• Continue surveillance for recurrent enterocolitis, which can occur even after apparently successful correction. Continue developmental and nutritional monitoring.