Cystic pilomatrixoma of the wrist mimicking a ganglion cyst in a child.

We describe a patient with a cystic pilomatrixoma mimicking a ganglion cyst on ultrasound. A 9-year-old boy had a subcutaneous mass on his left wrist. Ultrasound displayed a well-defined, multilobulated anechoic mass containing a few internal septa between the extensor pollicis longus and the extensor carpi radialis longus tendons. Sonographic findings suggested that the mass was a ganglion cyst. After excisional biopsy, histopathologic examination confirmed the diagnosis of pilomatrixoma.