Affected infants present shortly after birth with a large bowel obstruction secondary to transient dysmotility in the descending colon. Although the cause is unknown, immaturity of the colonic myenteric plexuses has been demonstrated in some cases. More than 50% of affected infants are born to mothers with diabetes. Other predisposing factors include hypoglycemia and sepsis.
Hypoglycemia stimulates the sympathetic nervous system and the vagus nerve. Sympathetic stimulation results in decreased peristalsis in the left colon, and vagal stimulation leads to increased motility to the level of the splenic flexure. Hyperglucagonemia, which may result from hypoglycemia or sepsis, also leads to decreased peristalsis in the left colon. Decreased motility results in increased absorption of water from the colon, which eventuates in the formation of abnormal meconium.
Infants with small left colon syndrome present with progressive abdominal distention, vomiting, and failure to pass meconium. Unusual late complications include bowel perforation and peritonitis.
Plain abdominal radiographs show dilated intestinal loops; air-fluid levels are seen frequently (A). A barium enema shows a small left colon, usually to the level of the splenic flexure, with proximal dilatation of the large bowel (B). The contrast enema is usually followed by rapid evacuation of meconium and decompression of the bowel, which relieves the condition. A rectal biopsy is warranted if symptoms of intestinal obstruction persist.