Melanosis coli refers to the dark pigmentation of the colonic mucosa in patients taking anthracene-containing laxatives. While this pigmentation is harmless, it is a clue to the patient's chronic cathartic laxative use.
The melanosis pigment is not taken up by adenomatous tissue, so detection of adenomatous polyps in the background setting of melanosis coli can make polyp detection easier, as evidenced here.
Fleshy white protuberances appearing at the anorectal junction, as often seen best on retroflexion view of the region, are benign post inflammatory lesions that are not clinically significant. These should not be confused with polyps, and do not require removal.
Hypertrophied papillae, as seen here, are generally multiple, whiteish yellow in appearance, and irregular in shape, making them distinguishable from polyps.
A sigmoid volvulus presents as an acute colonic obstruction, most often in the sigmoid colon. Here, the colon has a “candy wrapper” twist, causing an obstruction, with colonic dilatation proximal to this region. With gentle pressure, the colonoscope can be advanced through this region in order to decompress the region more proximally. However, this generally provides only temporary relief of the obstruction, as opposed to a permanent solution preventing future occurrence of the volvulus.
It is generally easy to discern when the scope is above the region of the sigmoid volvulus. The colon is generally dilated from air and stool filled, causing the lighting of the region to be diminished, and an overall dim appearance.
An acute infection with Clostridium difficile will cause an acute colitis of the colon. The hallmark lesions are whitish yellow exudative lesions, which on histologic examination have a characteristic “volcano eruption” appearance.
Typical appearance of C. difficile colitis. Following antibiotic therapy, the colonic mucosa will appear normal.