Simultaneous Carpal Tunnel Syndrome and Guyon's Canal Syndrome Caused by a Lipoma Arising From the Flexor Tenosynovium: A Case Report.

Carpal tunnel syndrome (CTS) is the most common peripheral entrapment neuropathy. While most cases are idiopathic, secondary CTS due to space-occupying lesions such as tumors is relatively uncommon. We report a rare case of simultaneous compression of the median nerve and the dorsal cutaneous branch of the ulnar nerve by a small lipoma arising from the flexor tenosynovium. Magnetic resonance imaging clearly demonstrated the lesion within the carpal tunnel and near Guyon's canal. Surgical excision led to resolution of median nerve symptoms, whereas ulnar sensory disturbance persisted due to involvement of the unrecognized dorsal cutaneous branch of the ulnar nerve. The patient later developed cubital tunnel syndrome, and concurrent compression of the dorsal cutaneous branch of the ulnar nerve complicated neurological assessment. This case emphasizes the need for comprehensive assessment and early MRI evaluation in atypical or unilateral CTS.