A 48-year-old man presented to our department with a 6-month history of progressive pain, numbness, and tingling around the medial epicondyle of the left elbow and the medial border of the forearm and hand. At the little finger, the two-point discrimination was 11 mm versus 6 mm on the right side. The patient had hand weakness with a decreased grip strength of 40 kg (right side, 50 kg) and pinch strength of 7 kg (right side, 19 kg). Froment's and Egawa's signs were positive, and there was atrophy of the adductor pollicis and first dorsal interosseous muscles. Electrophysiological studies demonstrated findings compatible with ulnar nerve compression (Table 1). At surgery, we found a fusiform epineural ganglion cyst (1.4 cm in diameter and 7.2 cm in length) encompassing the ulnar nerve in the cubital tunnel (Fig. 1). The proximal portion of the cyst was 1.4 cm superior to Struthers' ligament, and the distal portion extended into the right superior portion of Osborne's ligament; however, no connection to the elbow joint was found. The cyst contained a thick, jelly-like material. Under general anesthesia, we excised the ganglion cyst using microsurgery (Fig. 2) and performed ulnar nerve anterior transmuscular transposition (Fig. 3). Histology reported a "benign neural cyst with a myxoid matrix".

The patient was re-evaluated at 6 months postoperatively, both clinically and electrophysiologically. At 6 months, the patient was almost completely free of pain, tingling sensations, and numbness. In addition, his grip and pinch strength were improved and the adductor pollicis muscle wasting showed a dramatic recovery. A postoperative electrophysiological study showed some improvement, but the patient had not returned to normal at that time.

Our case has three distinct features. First, the fusiform epineural ganglion cyst had unique morphological characteristics. Specifically, it encompassed the ulnar nerve in the cubital tunnel. Second, the cyst did not originate from the medial aspect of the ulnohumeral joint. Finally, the clinical symptoms worsened gradually over a 6-month period, in contrast to reports of acute aggravation by a ganglion. Ganglia are not a common cause of peripheral nerve compression and have not been emphasized in the literature.1,2,5-10) Since the first report of a ganglion compressing the ulnar nerve in the hand,8) most studies have reported ganglia affecting the common peroneal nerve at the head of the fibula.7) Bowers and Doppelt2) reported that all ganglion cysts compressing the ulnar nerve in the cubital tunnel originated from the ulnohumeral joint and none were neural tissue. Ganglia commonly occur in middle-aged men, especially those with a history of elbow trauma.5,6) One case of ulnar nerve compression by a intraneural ganglion at the retrotrochlear groove was reported.5) That patient had symptoms for 3 months, no muscle atrophy was observed, and almost complete recovery of electrophysiological findings and clinical features were observed after ganglion excision. Boursinos and Dimitriou7) reported a patient who developed muscle wasting due to a longer symptomatic period; the ganglion was 2 cm in diameter, originated from the epineurium without being surrounded by nerve fibers, and had no connection to the elbow joint. In our case, the 6-month history of progressive symptoms in addition to the ganglion encompassing the nerve may explain the lack of complete recovery of electrophysiological parameters despite a significant clinical improvement 6 months postoperatively. Since ganglia are not a common cause of cubital tunnel syndrome, they are often misdiagnosed because preoperative imaging studies are not always performed. Since palpation before surgery revealed no evidence suggesting a mass in the cubital tunnel and the symptoms and physical examination made us suspect typical compressive neuropathy of the cubital tunnel, neither ultrasound (US) nor magnetic resonance imaging (MRI) was performed. MRI provides the best view of the cyst contents and its relationship to adjacent neurovascular structures. In addition, computed tomography and US may be useful. However, the patient's history, clinical symptoms, and electrophysiological findings are also sufficient for diagnosing typical compressive neuropathy. Total excision of the epineural ganglion may not always be possible without damaging the nerve, especially if the ganglion is intraneural.1-4) In all reported cases, an early diagnosis and careful excision was associated with a satisfactory outcome.5,6,9,10) Due to removed intermuscular septum, Osborne's ligament, flexor-pronator fascia during the exploration and excision for the ganglion, anterior transposition of the ulnar nerve was considered, as means of decompression and protection. As in other reports, the fusiform epineural ganglion was excised and ulnar nerve anterior transmuscular transposition, which the author prefers, was performed. At the 6-month follow-up, the patient was almost completely free of pain, sensory impairment, and numbness. Additionally, grip and pinch strength were improved and the adductor pollicis muscle wasting showed a dramatic recovery.