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FAP : Extraintestinal Lesions

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Extraintestinal Manifestations in Familial Adenomatous Polyposis: Besides intestinal polyposis, FAP or its variants can show bone abnormalities (osteomas of mandible, skull, and long bones; exostoses; dental abnormalities; mandibular cysts), desmoid tumors (Gardner syndrome), congenital hypertrophy of retinal pigment epithelium, epidermoid cysts, fibromas, and tumors of adrenal and thyroid gland.

Desmoid tumors develop in one-thirds of FAP patients and may be fatal. They show familial aggregation. The disease-causing mutations are distal to codon 1444 of the APC gene. They result from proliferation of mesenteric fibroblasts triggered by abdominal surgery (e.g. prophylactic colectomy). Rarely, they arise spontaneously. The fibrosis can cause GI obstruction and encase arteries, veins, ureters and other vital structures resulting in a mortality rate of 10-50%. The treatment usually consists of radiation when localized and a combination of sulindac (an NSAID) and tamoxifen (anti-estrogen) when the fibromatosis is more widespread.

The photograph from an FAP patient shows a colectomy specimen that was carpeted with a well over 1000 small adenomas.

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