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flat colorectal adenoma

Friday 9 March 2012

Flat Adenomas (Depressed colorectal adenomas)

Flat adenomas constitute a special subgroup of adenomas with a greater potential for malignant transformation while still small than is exhibited by exophytic adenomas.

The terms superficial, flat, and depressed adenoma are all used synonymously to describe this entity.

Flat adenomas can be single or multiple.

Because flat or depressed adenomas display little or no mucosal elevation, they can be very difficult to see endoscopically and patho-logically, especially in the proximal colon.

They areoften more clearly delineated endoscopically after spraying the mucosa with methylene blue or indigo carmine.

Endoscopically, flat adenomas are recognized as plaque-like lesions with vague redness or discoloration.

They tend to be small, usually not exceeding 1 to 2 cm in diameter.

Flat adenomas are much more readily identified in colectomy specimens following fixation than they are at the time of endoscopy, presumably because the gross features become highlighted following formalin fixation.

The failure to recognize these flat lesions may account for the lingering concept of "de novo colorectal carcinoma".

Depressed adenomas tend to arise more commonly in the right colon than elsewhere.

They occur in the HNPCC syndrome, sporadically, or in patients with FAP.

The frequency of flat adenoma is 50.7% in HNPCC patients.

Flat adenomas have a high incidence of high-grade dysplasia and a high association with synchronous and metachronous invasive colorectal carcinomas.

See also

- colorectal adenoma