Intraosseous epidermal cyst of the distal phalanx of the thumb: radiographic and magnetic resonance imaging findings.

We report conventional radiographic and magnetic resonance imaging (MRI) findings of an intraosseous epidermal cyst of the distal phalanx of the right thumb in a 39-year-old man. Conventional radiographs showed a sharply well-circumscribed osteolytic lesion of the distal phalanx with interruption of its tip. The osteolytic lesion itself showed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images without contrast enhancement. However, the soft tissues surrounding the osteolytic lesion demonstrated contrast enhancement on MRI. The combined conventional radiographic and MRI findings suggested the diagnosis of intraosseous epidermal cyst rather than enchondroma, giant cell tumor, intraosseous glomus tumor, aneurysmal bone cyst, or simple bone cyst.