Guyon's canal lipoma causing ulnar neuropathy.

Abstract

64-year-old man presented with a chronic history of ulnar-sided pain and paresthesia in his left hand. The physical examination revealed a soft-tissue mass in the palmar aspect of the wrist. Radiographs showed a radiolucent soft-tissue mass in the volar aspect of the wrist (Fig. 1A). The MR examination revealed a lipomatous mass in Guyon’s canal that splayed the ulnar artery and nerve and displaced the carpal tunnel radially (Figs. 1B and 1C). The mass was completely excised. Histology showed mature adipose tissue consistent with a lipoma (Fig. 1D). Guyon’s canal is also known as the “pisohamate tunnel” or the “distal ulnar tunnel.” The roof of the tunnel consists of the palmar carpal ligament, the palmaris brevis, and the hypothenar fat and fibrous tissue. The tendons of the flexor digitorum profundus, the transverse carpal ligament, the pisohamate and pisometacarpal ligaments, and the opponens digiti minimi form the floor of the tunnel. The medial wall includes the flexor carpi ulnaris, the pisiform, and the abductor digiti minimi manus. The tendons of the extrinsic flexors, the transverse carpal ligament, and the hook of the hamate constitute the lateral wall. Guyon’s canal consists of three zones. Zone 1 extends from the proximal edge of the palmar carpal ligament to the bifurcation of the ulnar nerve. Zones 2 and 3 are adjacent to each other, extending from the bifurcation of the ulnar nerve just distal to the fibrous arch of the hypothenar muscles. These zones contain the deep motor branch and the superficial sensory branch of the ulnar nerve, respectively. Clinical symptoms correlate with the zone in which ulnar nerve compression occurs: combined motor and sensory deficits occur in zone 1 lesions; pure motor deficits, in zone 2 lesions; and isolated sensory deficits, in zone 3 lesions. Compressive neuropathies of the ulnar nerve occur most commonly at the elbow and less commonly at the wrist [1]. The most common causes of ulnar nerve compression at the wrist are ganglia, fractures, anomalous muscles, thrombosis, bursitis, and a thickened pisohamate ligament [2]. Repeated blunt trauma to the hypothenar area may cause ulnar neuritis,