Congenital megacolon, also known as aganglionosis or Hirschsprung disease (HD), occurs due to persistent spasms in the distal segment of the rectum or colon, leading to fecal retention in the proximal colon, which subsequently becomes hypertrophied and dilated. This condition is one of the most common congenital intestinal malformations in infants, with an incidence rate of approximately 1 in 5,000 to 1 in 2,000 live births. The male-to-female ratio is between (3:1) and (4:1), and it has a hereditary predisposition.
Etiology and Pathophysiology
The disease results from a combination of polygenic inheritance and environmental factors. The primary pathological change is the absence of ganglion cells in the neural plexuses within the muscle and submucosal layers of the spastic segment of the intestine. There is an increased number of unmyelinated parasympathetic nerve fibers that are hypertrophied, thickened, and tightly intertwined. In the dilated segment, the muscle layer becomes hypertrophic, the mucosa inflamed, and small ulcers may be present, while the ganglion cells in the muscle and submucosal layers remain normal.
In terms of morphology, the affected bowel is divided into three parts: the spastic segment, the transition segment, and the dilated segment. Beyond the formation of megacolon, other physiological effects include the loss of normal defecation reflexes. Based on the length of the spastic segment, Hirschsprung disease can be classified into:
- Common Type (approximately 85% of cases).
- Short-Segment Type (about 10%).
- Long-Segment Type (approximately 4%).
- Total Colonic Type (around 1%).
- Total Intestinal Type (extremely rare).
Clinical Manifestations
Delayed Passage of Meconium, Persistent Constipation, and Abdominal Distension
Most affected newborns fail to pass meconium or pass only small amounts within 24–48 hours after birth. Symptoms of low intestinal obstruction may become apparent between the second and third day. Persistent constipation follows, with bowel movements occurring every 3–7 days, or even as infrequently as once every 1–2 weeks. Severe cases may show complete dependence on enemas for defecation. The longer the length of the spastic segment, the earlier and more severe the constipation. Abdominal distension progressively worsens, with a tight, shiny abdominal wall, visible venous dilation, intestinal loops, and peristaltic waves. Increased diaphragmatic elevation may result in respiratory distress.
Vomiting, Nutritional Deficiencies, and Growth Retardation
Intestinal obstruction leads to vomiting, which is usually mild and contains bile, but severe cases may exhibit fecal-like vomitus. Chronic abdominal distension and constipation impair the child’s appetite and nutrient absorption, resulting in growth retardation, weight loss, anemia, and hypoproteinemia with accompanying edema.
Rectal Examination
The rectal ampulla is typically empty. Upon withdrawal of the examining finger, a large amount of foul-smelling gas and stool is expelled due to fecal accumulation in the proximal colon.
Complications
Enterocolitis
Enterocolitis is the most common complication and can occur at any age, especially in neonates. Intestinal obstruction in the distal segment causes significant colonic dilation. Increased intraluminal pressure leads to ischemia of the intestinal mucosa, weakening its barrier function and allowing bacterial toxins and metabolic by-products to enter the bloodstream. The affected child may develop high fever, severe abdominal distension, vomiting, and foul-smelling, bloody diarrhea. Mucosal ischemia can result in edema and ulcers, leading to bloody stool and intestinal perforation. Severe cases may involve inflammation extending into the muscle layer, causing serosal congestion, edema, and thickening, which may lead to exudative peritonitis. Vomiting, diarrhea, and the accumulation of intestinal fluid in the dilated bowel quickly result in dehydration and metabolic acidosis, with a high risk of mortality.
Intestinal Perforation
Intestinal perforation is more common in neonates, particularly in the sigmoid colon and cecum.
Secondary Infections
Complications such as sepsis or pneumonia may occur.
Auxiliary Examinations
X-Ray Imaging
Diagnosis is often confirmed using X-ray imaging.
Abdominal Upright Plain X-Ray
This typically shows low incomplete intestinal obstruction, proximal colonic dilation, and absent or minimal gas in the pelvis.
Barium Enema Study
This method has a diagnostic accuracy of approximately 90%. It reveals characteristic findings, including the spastic segment, transition segment, and dilated segment, forming a "funnel-like" appearance. Impaired barium evacuation from the dilated bowel above the spastic segment and mucosal thickening with "saw-tooth" changes suggest concurrent enterocolitis.
Rectal and Anal Pressure Testing
Reflex pressure changes in the internal and external anal sphincters are measured. Affected children often lack the reflexive relaxation of the internal sphincter, resulting in a negative recto-anal inhibition reflex (RAIR). Neonates under two weeks old may exhibit false negatives, limiting the applicability of the test in very young infants.
Rectal Mucosal Suction Biopsy
Histochemical analysis evaluates mucosal acetylcholine levels and cholinesterase activity. However, diagnostic accuracy for neonates is low. Immunohistochemical methods can detect neuron-specific enolase and other markers.
Full-Thickness Rectal Biopsy
Full-thickness biopsy involves sampling bowel tissue from the rectal wall at a depth including the muscle layer. Hematoxylin and eosin staining is used to determine the presence and density of ganglion cells. Affected bowel segments lack ganglion cells and demonstrate proliferated, thickened unmyelinated nerve fibers.
Diagnosis and Differential Diagnosis
Delayed or absent passage of meconium in neonates, accompanied by abdominal distension and vomiting, suggests the possibility of congenital megacolon. Infants and young children with a history of chronic constipation and abdominal distension should undergo specific diagnostic evaluations. The disease requires differentiation from the following conditions:
Neonatal Period
Meconium Plug Syndrome (Meconium Obstruction of the Newborn)
This condition occurs due to the thick and concentrated consistency of meconium, leading to transient low intestinal obstruction. Symptoms resolve after enema evacuation of the meconium, and normal bowel movements resume without recurrence.
Congenital Intestinal Atresia
This condition can involve any part of the intestinal tract in neonates, with ileal atresia being the most common. It presents with symptoms of intestinal obstruction. Rectal examination reveals only small amounts of gray-white jelly-like stool, and saline enemas fail to induce defecation. An upright abdominal X-ray shows absence of gas in the lower abdomen, and contrast imaging confirms the diagnosis.
Neonatal Necrotizing Enterocolitis (NEC)
Differentiating NEC from congenital megacolon complicated by enterocolitis can be challenging. NEC commonly occurs in premature infants, often with a history of perinatal asphyxia, hypoxia, infection, or shock, and is frequently accompanied by bloody stool. Abdominal X-rays may show pneumatosis intestinalis (air in the intestinal wall) and/or portal venous gas.
Infant and Childhood Period
Secondary Megacolon
Organic lesions at the anus or distal rectum, such as congenital anal stenosis, postoperative cicatricial strictures, or extrinsic compression from rectal tumors, can cause defecation difficulty, fecal retention, and secondary colonic dilatation. Digital rectal examination can confirm these conditions.
Functional Constipation
Functional constipation is a chronic condition of unknown etiology and can be categorized as slow-transit type, outlet-obstruction type, or mixed type. It is characterized by infrequent bowel movements, difficulty during defecation, hard or pellet-like stools, and a sensation of incomplete evacuation. Some individuals may require manual assistance (manual evacuation) to pass stool. A diagnosis is made after ruling out organic diseases.
Treatment
Definitive treatment involves surgical resection of the aganglionic segment and part of the dilated colon. Many complications of congenital megacolon occur within the first two months of life, necessitating special attention during this period.
Conservative Treatment
Oral Medications
Laxatives or lubricants are administered to aid defecation.
Local Measures
Glycerin suppositories and anal dilatation can be used to stimulate the sphincter and induce defecation.
Enemas
This involves inserting a rectal catheter beyond the stenotic segment and injecting saline once daily. Abdominal massage facilitates the evacuation of both enema fluid and fecal matter. Repeated sessions help gradually clear the accumulated stool.
Surgical Treatment
Surgical options include colostomy and definitive corrective surgery. Conditions warranting colostomy include cases complicated by uncontrolled enterocolitis, malnutrition, high fever, anemia, severe abdominal distension, or situations where the patient is unable to tolerate definitive surgery. It also applies to cases with significant respiratory compromise due to severe abdominal distension or when conservative measures prove ineffective.
Early corrective surgery is now often advocated. It is generally considered appropriate to perform definitive surgery in patients with a body weight above 3 kg and stable overall condition.