Sigmoidoscopy involves the insertion of a thin lighted instrument, the
sigmoidoscope, into the rectum to inspect the lining of the colon (the large intestine).
Similar to the flexible
sigmoidoscope, the colonoscope is a longer tube that allows the health care professional to examine the entire large intestine.
A study from Albert Einstein Medical Center in Philadelphia found that the percentage of cancers within reach of a flexible
sigmoidoscope declined from 65% in 1985 to 48% from 1985 to 1998.
With the arrival of fiber optics, it became possible to look directly at the inside of the colon--first through a short, flexible tube (the flexible
sigmoidoscope) and later, through a much longer version of the same instrument, the colono-scope, which extends four to six feet into the colon.
Colorectal cancer detection with the 60 cm flexible
sigmoidoscope in a solo general internist's office.
The most commonly used instrument is the rigid
sigmoidoscope, a metal instrument about 10 inches long that can view the interior of the rectum and the lower colon.
Of these 184 adenomatous polyps, 106 (58%) were potentially within reach of the flexible
sigmoidoscope. Only three adenocarcinomas were discovered during the entire study period.
During his clinical practice, the index physician (W.H.) realized that many of the patients examined with the flexible
sigmoidoscope actually required examination of the entire colon.
Only one of the four Dukes stage C cancers detected by FOBT was in the descending colon, sigmoid, or rectum and thus was potentially within reach of the flexible
sigmoidoscope. The other five patients with colorectal cancers who were compliant with the screening recommendations had their cancers detected after they were symptomatic, qualifying as false-negative FOBTs.