Arteriovenous Malformation of the Thenar Region: A Diagnostic Challenge.

Arteriovenous malformations (AVMs) of the hand are rare, high-flow vascular anomalies that present diagnostic and therapeutic challenges owing to variable clinical manifestations and complex regional anatomy. We report a 38-year-old man with a 2-year history of a painful, progressively enlarging mass in the right thenar region associated with impaired grasp and pinch. Initial evaluation with radiographs and ultrasound was nondiagnostic. Magnetic resonance imaging demonstrated a well-circumscribed lesion in the first web space but did not reliably characterize its vascular nature. Complete surgical excision was undertaken. Histopathological analysis demonstrated a proliferation of arterial and venous channels within a fibroadipose stroma, consistent with a type B AVM. At 2-year follow-up, there was no evidence of recurrence and functional outcomes were satisfactory. This case underscores the limitations of conventional imaging in detecting high-flow vascular lesions of the hand and highlights the importance of maintaining diagnostic suspicion for AVMs in atypical soft tissue masses.