Teaching NeuroImages: Ganglion cyst causing pure sensory ulnar neuropathy at the wrist.

A 32-year-old woman presented with left wrist pain and tender mass at the wrist for 1 month. She described left 4th and 5th digit tingling which worsened with palpation of the mass. Sensory nerve action potential of the digital sensory branch of the left ulnar nerve was of low amplitude and prolonged distal latency. Motor conduction studies and needle EMG were normal. Wrist MRI (figure) showed a ganglion cyst compressing the ulnar nerve which was surgically removed with partial improvement in the patient’s symptoms. Ganglion cysts at the wrist are frequent and benign but can occasionally compromise the median or ulnar nerve as shown in this case.1