Bowler's thumb: ultrasound diagnosis of a neuroma of the ulnar digital nerve of the thumb.

Bowler's thumb is a rare traumatic neuropathy of the ulnar digital nerve of the thumb. We present a case of bowler's thumb in a 21-year-old male recreational bowler who presented with a painful mass on the ulnar side of the right thumb. Magnetic resonance (MR) imaging of the hand was inconclusive. However, subsequent ultrasound (US) showed asymmetric enlargement of the ulnar digital nerve of the thumb with marked epineural thickening corresponding to the palpable mass, confirming the clinical diagnosis of bowler's thumb. Although this condition is typically diagnosed clinically, imaging can help to clarify clinical findings. In our experience, MR imaging is a clinician's preferred choice when further evaluating physical findings of digital nerve pathology despite the lack of evidence to support MR as a primary imaging modality for these patients. This case illustrates the role that US can play as an initial imaging modality for the evaluation of small peripheral nerves.