Findings: Loops of markedly dilated colon down to the level of the rectum. There is a relative narrowing of the rectum with respect to the sigmoid colon, resulting in abnormal retrosigmoid index. The distal sigmoid colon gradually dilates up to become markedly dilated, and the rectum appears to be of normal caliber.

Diagnosis: Hirschsprung's disease.

Discussion: Hirschsprung's disease occurs in one out of 4500 live births. It affects more commonly boys and children with Down's syndrome. It is characterized by an absence of ganglion cells and myenteric plexus, secondary to failure of neuroblastic migration. It affects most commonly the distal sigmoid and the rectum (70%). 15% of cases of Hirschsprung's disease appear to involve the bowel proximal to the splenic flexure. Diagnosis is usually made in the first month of life. It presents with the failure of the child to pass meconium within the first 24 hours and the child also appears to have abdominal distention. Minority of patients can present with enterocolitis.

Conventional abdominal x-ray usually demonstrates low obstruction with multiple air fluid levels and bowel distention. The differential diagnosis usually includes imperforate anus, colonic atresia, Hirschsprung's disease, meconium plug and meconium ileus. Barium enema is usually useful in diagnosing Hirschsprung's disease, and is performed to evaluate for a transition zone. In Hirschsprung's disease the enema demonstrates an essentially normal caliber rectum and at some point in the upper rectum or distal sigmoid, there is an abrupt transition to an area of grossly dilated bowel. The rectosigmoid index is used to evaluate for a transition zone. A rectum to sigmoid ratio of greater than .9 exclude the diagnosis of Hirschsprung's disease.

Once the disease is diagnosed the management is usually surgical.

References:
Eisenberg RL. Gastrointestinal Radiology, a Pattern Approach, 2nd Edition, 1990.

Blickman H. Pediatric Radiology, the Requisites, 2nd Edition, 1998.

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