MSH: A tumor composed of cells resembling those of the hair matrix, which undergo 'mummification' and may calcify. It is a relatively uncommon tumor, which may occur at any age from infancy. The majority of patients are under 20, and females are affected more than males. The lesion is usually a solitary deep dermal or subcutaneous tumor 3-30 mm in diameter, situated in the head, neck, or upper extremity. (From Rook et al., Textbook of Dermatology, 4th ed, p2401),NCI: A benign adnexal neoplasm arising from hair-bearing skin surfaces, usually the head and neck and upper extremities. It usually presents as a solitary, slow-growing nodular mass. Morphologically, it displays differentiation towards the matrix and inner sheath of the normal hair follicle and the hair cortex. Complete surgical excision is usually curative. Occasionally, it may recur.,NCI: A benign adnexal neoplasm arising from hair-bearing skin surfaces.