Sigmoidoscopy and Anoscopy

These procedures permit examination of the distal large bowel without extensive preparation or sedation. Disease within the anal canal is best seen with an anoscope--a short tubular instrument with an acutely angulated bevel that allows direct visualization of the canal and the distal rectum. The rigid sigmoidoscope, when passed to its full length of 25 cm, permits inspection of the rectum and distal sigmoid colon. The 60-cm flexible sigmoidoscope permits inspection of the rectum, sigmoid, and most of the descending colon.

Performing a digital rectal examination along with sigmoidoscopy and anoscopy allows the physician to discover and treat precancerous polyps. It is important to discover and remove benign lesions within 6 cm of the anus (the area in which cancer usually requires removal of the rectum and anus), and thus avoid the need for colostomy if the lesions become malignant.

Indications

The flexible sigmoidoscope may be used to evaluate the left side of the colon, where two thirds of neoplasms appear. Rigid or flexible sigmoidoscopy can evaluate the distal colon for suspected disease; either procedure may complement a barium enema. Anoscopy is best suited for visualizing perianal problems (eg, fissures, fistulas, hemorrhoids).

Sigmoidoscopy and anoscopy are valuable for early detection of most colorectal polyps and cancer, which increase in incidence with age and have a predominantly left-sided distribution. For an asymptomatic person, sigmoidoscopy is recommended every 3 to 5 years for patients > 50 years to diagnose adenomas at a stage when their removal will prevent development of colorectal cancer. If polyps are discovered during flexible sigmoidoscopy, they should not be removed because more extensive preparation and complete evaluation of the colon are required.

Contraindications

A recent myocardial infarction contraindicates this procedure. Flexible sigmoidoscopy should not be substituted when indications for colonoscopy (anemia, positive results of a fecal occult blood test, polypectomy) are present.

Procedure and Complications

One or two phosphate enemas cleanse the bowel adequately. Sedation is not required. The patient usually lies on the left side for flexible sigmoidoscopy but assumes the knee-chest position for rigid sigmoidoscopy or anoscopy.

Complications are extremely rare but may include perforation. Air insufflation or instrument looping in the colon may cause cramps and discomfort.