Compression of the ulnar nerve in Guyon's canal caused by a large hypothenar cyst

Abstract

Objective: We report the case of a 77-year-old man who presented with a long-standing, large swelling of the left hypothenar eminence. This was associated with recent-onset paresthesia and numbness of the ring and little fingers. Magnetic resonance imaging demonstrated a cystic lesion that occupied almost the entire bulk of the hypothenar eminence.

Methods: Surgical exploration revealed a 7-cm, encapsulated, yellow-brown cyst, around which were stretched the superficial sensory branches of the ulnar nerve. The hypothenar musculature lay flattened against the deep border of the mass.

Results: The cyst was removed and Guyon's canal was released. Histologic examination confirmed a large cyst containing proteinaceous debris and blood breakdown products. It might have resulted from hemorrhage into a long-standing ganglion. Removal of the cyst led to full resolution of the patient's symptoms.

Conclusions: This represents an unusual cause of ulnar tunnel syndrome. It is rare to encounter such a large cyst in the hand and interesting in the sense that the resulting symptoms were relatively mild and took many years to develop.

Figure 1

Patient's left hand showing large hypothenar mass.

Figure 2

Axial T2-weighted magnetic resonance imaging scan showing loculated lesion (C) of high signal intensity lying in the hypothenar eminence adjacent to Guyon's canal (white arrow).

Figure 3

Intraoperative view of the cyst (C) intimately associated with the superficial sensory branches of the ulnar nerve (N). A indicates ulnar artery; FCU, flexor carpi ulnaris tendon inserting onto pisiform.

Figure 4

Photomicrograph of the specimen showing fibrotic wall and proteinaceous debris and blood breakdown products with numerous cholesterol clefts inciting a giant cell response (H and E; magnification × 20.)