Review Question - QID 213015

A 55-year-old patient presents with numbness and tingling in the right small and ring fingers and associated hand weakness. On examination, there is decreased sensation on the volar, ulnar and radial aspect of the small finger and the volar, and ulnar aspect of the ring finger, but the sensation on the dorsum of the hand is preserved. Symptoms are reproduced with pressure over the wrist during flexion. There is weakness of finger adduction and grip strength, but flexor digitorum profundus strength of the ring and small finger remains preserved. The patient denies any previous trauma to the right hand or wrist. What study would most likely identify the causative lesion?