BACKGROUND Animal studies have shown that the neuromuscular structures on the luminal side of the colonic circular muscle coordinate circular muscle activity. These structures have been identified by electron microscopy in the normal human colon, but have never been thoroughly studied in patients with acquired intestinal hypoganglionosis.

AIMS To perform histological, immunocytochemical, and electron microscopic examinations of the colon of a patient with acquired intestinal hypoganglionosis presenting as megacolon.

PATIENT A 32 year old man with a one year history of constipation and abdominal distention, a massively dilated ascending and transverse colon, and a normal calibre rectum and descending and sigmoid colon. He had a high titre of circulating serum anti-neuronal nuclear antibodies.

RESULTS The number of ganglion cells and nerve trunks was decreased throughout the colon. Disruption of the neural network and a loss of interstitial cells of Cajal were observed on the luminal side of the circular muscle; in their place, the non-dilated colon contained a hypertrophic fibromuscular layer.

CONCLUSIONS Striking architectural alterations occurred at the site regarded as the source of the coordination of colonic circular muscle activity in an adult patient with acquired intestinal hypoganglionosis presenting as megacolon.