Intermetatarsophalangeal bursitis induced by a plantar epidermal cyst.

A 44-year-old woman was admitted to the authors' institution for evaluation of two masses in the right forefoot. Standard radiographs showed foci of calcification within the mass. Magnetic resonance imaging and macroscopic findings during surgery revealed the lesion was composed mainly of two different portions: dorsal cystic masses and a solid mass in the plantar side of the fifth metatarsal head. Histologic and immunohistochemical examinations showed that the former was an intermetatarsophalangeal bursitis induced by keratinous material, whereas the latter was a ruptured epidermal cyst. To the best of the authors' knowledge, the current case is the first report of intermetatarsophalangeal bursitis caused by an untreated epidermal cyst.