CLINICAL CONSIDERATIONS OF SIGMOID COLON 1. Colonic aganglionosis (Hirschsprung disease)
It is caused by the arrest of the caudal migration of neural crest cells. The hallmark is the absence of ganglionic cells in the myenteric and sub-mucosal plexuses, most commonly in the sigmoid colon and rectum, resulting in a narrow segment of colon (i.e., the colon fails to relax). Although the ganglionic cells are absent, there is a proliferation of hypertrophied nerve fiber bundles. The most characteristic functional finding is the failure of the internal anal sphincter to relax following rectal distention (i.e., abnormal rectoanal reflex). Mutations of the RET proto-oncogene (chromosome 10q.11.2) have been associated with Hirschsprung disease. Clinical findings include a distended abdomen, inability to pass meconium, gushing of fecal material upon a rectal digital exam, fecal retention, and a loss of peristalsis in the colon segment distal to the normal innervated colon. The barium radiograph shows a narrowed rectum and a classic transition zone (arrows). The upper segment (*) of the normal colon is distended with fecal material. The distal segment (**) of the colon is narrow and is the portion of colon where the myenteric plexus of ganglion cells is absent.
It is the presence of diverticula (abnormal pouches or sacs) most commonly found in the sigmoid colonin patients older than 60 years of age. It is associated with a low-fiber, modern Western-world diet. Perforation and/or inflammation of the diverticula result in diverticulitis.
Clinical findings include pain in the left lumbar region, palpable inflammatory mass in the left lumbar region, fever, leukocytosis, ileus, and peritonitis. The post-evacuation barium radiograph shows numerous small out-pouchings or diverticula (arrows) from the colonic lumen. These diverticula are filled with barium and fecal material.
3. Flexible sigmoidoscopy permits examination of the sigmoid colon and rectum. During sigmoidoscopy, the large intestine may be punctured if the angle at the rectosigmoid junction is not negotiated properly. At the recto-sigmoid junction, the sigmoid colon bends in an anterior direction and to the left. During sigmoidoscopy, the transverse rectal folds (Houston valves) must be negotiated also.i
4. Colostomy. The sigmoid colon is often used in a colostomy due to the mobility rendered by the sigmoid mesocolon (mesentery). An ostomy is an intestinal diversion that brings out a portion of the gastrointestinal (GI) tract through the rectus abdominis muscle. A colostomy may ablate the pelvic nerve plexus, which results in loss of ejaculation, loss of erection, urinary bladder retention, and decreased peristalsis in the remaining colon.