Familial cylindromatosis: A genetic syndrome in which numerous benign tumors of skin adnexa (such as the sweat glands) develop, principally on the head and neck. This disorder is inherited in an autosomal manner and is caused by mutation of the CYLD gene on chromosome 16q12-q13. Mutation of CYLD has been likened to having faulty brakes on a car. Instead of a pileup of cars, a pileup of cells results. Topical application of aspirin, another type of brake on cell proliferation, may possibly be useful. Also called the turban tumor syndrome.