Ganglion Cyst in Zone 2 of Guyon's Canal Causing Ulnar Neuropathy With Claw Hand Deformity: A Case Report and Literature Review.

Guyon's canal, a fibro-osseous anatomical tunnel, sometimes harbors underlying pathologies such as a ganglion cyst, leading to symptoms including dysesthesia, paresthesia, and motor weakness in the ulnar nerve distribution. Surgical excision is often the recommended approach to restore normal hand function. Ulnar nerve palsy caused by mechanical compression can benefit from surgical decompression; however, a timely diagnosis is often difficult. In this report, we describe the successful tumor excision and nerve decompression of a ganglion cyst in Guyon's canal. The observed intraoperative findings challenge the conventional classification of compression zones. The processes of diagnosing and treating tumors within Guyon's canal were thoroughly explained and elaborated. A 40-year-old female patient presented with right-sided ulnar wrist pain, progressive weakness of the intrinsic muscles, and a claw hand deformity, typically suggestive of a zone 1 compression within Guyon's canal. Magnetic resonance imaging revealed a cystic mass at the ulnar side of the wrist, prompting a referral to the Department of Plastic and Reconstructive Surgery for further management. Intraoperatively, a transparent cystic tumor was identified in zone 2 of the Guyon's canal, causing significant compression of the motor branch, while displacing the superficial branch upward, which mimicked the clinical presentation of zone 1 compression. The tumor was excised, and the nerve was successfully decompressed. A pathological report confirmed the diagnosis of a ganglion cyst. At the 1-year follow-up, the patient showed no signs of complications or recurrence. Her initial symptoms, including pain and intrinsic muscle weakness, improved significantly. Complete resolution of claw hand deformity indicated successful functional recovery. Compression of the ulnar nerve within Guyon's canal due to a ganglion cyst is uncommon, and the significance of the resulting neuropathy in the wrist is underrated. Meticulous clinical assessments, a thorough anatomical understanding and appropriate tests, are essential for accurate diagnosis. Timely decompression and surgical removal of the ganglion can facilitate a promising postoperative recovery.