Ulnar Neuropathy Caused by a Giant Epidermal Cyst at the Elbow: Case Report

Abstract

Here, we report an unusual case of ulnar neuropathy at the elbow caused by a giant epidermal cyst. A 76-year-old man was assessed on an outpatient basis for ulnar numbness of the left hand that had persisted for 6 months. A soft, elastic subcutaneous mass 6 cm in size was noted on his left elbow. He felt numbness on the ulnar aspect of the left fourth and fifth fingers, corresponding to the area innervated by the ulnar nerve, which worsened upon elbow flexion. An electrophysiological study revealed ulnar neuropathy at the elbow. To remove the subcutaneous mass at the left elbow and open up the ulnar tunnel, surgery was performed. There were no signs of nerve impingement or a neuroma on the ulnar nerve. The histological diagnosis was an epidermal cyst. On the day after surgery, numbness on the ulnar aspect of the left hand upon elbow flexion was markedly abated.

Keywords: cubital tunnel syndrome; epidermal cyst; ulnar neuropathy at the elbow.

Fig. 1

A. Photographs of the left elbow showing the large mass at the posterior side of the olecranon. B. An electrophysiological sensory nerve action potential study of the left ulnar nerve (left ulnar–digit V antidromic nerve). C. An electrophysiological compound muscle action potential study of the left ulnar nerve (left ulnar–ADM 3). D. Axial T1WI of the left elbow showing a well-defined mass (white arrow, mass; yellow arrow, ulnar nerve). E. Axial T2WI of the left elbow showing a well-defined mass.

Fig. 2

A. Intraoperative photograph showing a subcutaneous tumor mass. B. Photomicrograph of hematoxylin–eosin stain showing a cystic lesion lined by stratified squamous epithelium and containing layers of keratotic debris. C. A histological examination of the cystic lesion.