Proximal Megacolon in an Adult

Abstract

A44-year-old woman, born and residing in the United States, presented with medically nonresponsive chronic constipation, requiring 1 gallon of polyethylene glycol electrolyte solution weekly to induce bowel movements. She consistently experienced incomplete evacuation. She was hospitalized once for suspected sigmoid volvulus that spontaneously resolved. Physical examination showed a distended tympanitic abdomen with palpable stool in the left lower quadrant. Rectal examination revealed a high resting anal sphincter tone and no coordinated perineal descent during simulation of defecation; these features were confirmed on anorectal manometry (high squeeze anal sphincter pressure and requirement of 200 g to facilitate 50-mL balloon evacuation from the rectum). Gastric emptying was normal, and colonic transit was delayed. She was diagnosed with pelvic floor dyssynergia and symptoms improved somewhat after biofeedback therapy. A plain abdominal radiograph (Figure A) showed a dilated colon, confirmed on computerized tomography scan. Sagittal views of the abdominal computerized tomography (Figure B) showed an elongated, dilated proximal colon with a decompressed rectum. Direct endoscopic visualization of the intersection of the dilated and nondilated colon showed no mass or constrictions. Because of persistent symptoms and megacolon, she underwent colectomy at another hospital. Figure C shows the resected specimen with a dilated ascending and transverse colon, normal-caliber descending colon and rectum, and no constricted transition zone between dilated and normal-caliber segments. No pathologic examination of the colon was available. The enteric nervous system is derived from vagal and sacral neural crest cells. Vagal neural crest cells migrate caudally through the entire length of the gastrointestinal tract and provide the majority of neurons and glia. The sacral neural crest cells migrate rostrally and contribute to the innervation of the distal colon and rectum. Colonic dysganglionosis presents as a continuous spectrum, ranging anatomically from hypoganglionosis in colonic sections of different lengths and distributions to a localized constriction with proximal dilatation in Hirschsprung disease (HD). Hypoganglionosis is a decrease vs a complete lack of ganglia, and it can present as localized or generalized megacolon, or it may occur concomitantly with HD. These disorders present with long-term constipation refractory to medical therapy. Although approximately 95% of HD cases are diagnosed before the age of 5, less severe cases may present after 10 years of age and are considered adult HD.