Segmental dilatation of the colon is a very rare disease entity of unknown etiology and may mimic Hirschsprung's disease. It is characterized by dilatation of a segment of the colon of variable length with obstruction due to lack of peristalsis in a normally innervated intestine. Recently authors experienced a case of segmental dilatation of the sigmoid colon in a 6 month-old male, who presented with severe constipation, abdominal distention, and abdominal mass since 2 months of age. Down's syndrome and congenital nystagmus were associated. Barium enema demonstrated focal dilatation of the sigmoid colon, but the rectum and descending colon proximal to the affected colon were of normal caliber. Rectal suction biopsy with acetylcholinesterase staining was normal and anorectal manometry showed normal rectosphincteric reflex. At operation, there was a massively dilated and hypertrophied sigmoid colon with increased tortuous serosal vessels, measuring 15 cm in length and 10 cm in width. Teniae coli were identifiable in the affected segment. Frozen section biopsies at the proximal, affected, and distal colon showed ganglion cells. Descending loop colostomy was constructed initially and segmental resection and end to end colocolostomy were carried out 3 months later. Final histologic examination showed 1) normal colonic mucosa with ganglion cells, 2) prominent submucosal fibrosis and marked muscular hypertrophy, 3) unremarkable acetylcholinesterase activity and immunohistochemical findings against S-100 protein. On 8 months follow-up, he has been doing well and moves bowels 1-2 times daily.

The acetylcholinesterase(ACHE) activity in 37 biopsies from the patients with Hirschsprung's disease was analyzed for histochemical patterns according to age, and its evolutional behavior was also assessed. The histochemical criterion used for the diagnosis of Hirschsprung's disease was that of Chow, i.e., “the presence of many coarse discrete cholinergic fibers in the muscularis mucosae and in the immediately subjacent submucosa regardless of an infiltration of cholinergic fibers in the lamina propria.” The acetylcholinesterase activity in Hirschsprung's disease was further classified into 3 patterns, advocated by de Brito and Maksoud: Pattern I-many thick fibers exclusively in the muscularis mucosae and submucosa(newborn pattern). Pattern II-many thin fibers in the muscularis mucosae and submucosa with a clear infiltraiton of cholinergic fibers in the lamina propria(classical pattern). Pattern III-an intermediate pattern showing morphological characteristics of the two patterns with predominance of one or the other. Of 37 biopsies, Pattern 1 was seen excusively in 16 biopsies taken from the neonates. Pattern III was 11 of 37 biopsies and it was mainly seen in children between 2 to 12 months of age. Pattern II was seen in all 3 biopsies of older than 1 year of age and in 6 ones of 3 to 12 months of age. In summary, this study reinforces the impression that there is an evolutional character of the distribution and morphology of the cholinergic ACHE positive fiber with age. In other words, ACHE activity in Hirschsprung's disease appears to evolve with age from the newborn pattern to the intermediate pc.ttern finally to the classical pattern.