Subungual keratoacanthoma: ultrasound and magnetic resonance imaging findings.

Subungual keratoacanthoma is a rare, squamoproliferative neoplasm arising at the nail bed. It may cause erosion of the underlying bone. We report a case of subungual keratoacanthoma of the right thumb in a 63-year-old man. Radiographs showed cortical erosion of the distal phalanx of the right thumb. Ultrasonography showed a mixed echoic tumor. On magnetic resonance imaging (MRI), the tumor showed intermediate signal intensity on T1-weighted images and mixed intermediate and high signal intensity on T2-weighted images with peripheral thin rim enhancement.