A rare presentation of cubital tunnel syndrome by accessory anconeus muscle

Abstract

Cubital tunnel syndrome (Cu TS) is the second most frequent upper extremity compressive neuropathy after carpal tunnel syndrome. Cu TS is idiopathic; however, it has been linked to ulnar nerve vulnerability and anconeus epitrochlearis (AE) muscle hypertrophy. Although there are few studies in the literature that reveal AE muscle as one of the causes of Cu TS, its prevalence is low. The goal of this case report is to raise awareness regarding the existence of AE muscle as a potential cause of Cu TS, as well as the imaging findings of Cu TS in magnetic resonance imaging (MRI). A 17-year-old male patient complained of intermittent pain in the medial aspect of the left elbow and paresthesia in the left hand. Examination revealed hyperextension of meta carpalphalangeal joints and flexion of proximal interphalangeal joints of the 4th and 5th digits, besides the sensory deficit along the ulnar border of the 5th digit. A nerve conduction study revealed non-stimulable sensory and motor components of the right ulnar nerve. MRI with T1-weighted fast spin echo, Fat sat proton density-weighted, and gradient echo T2*-weighted sequence showed AE - on the posteromedial aspect of the elbow. The ulnar nerve within the cubital tunnel appeared thickened and edematous with bright perineural fat signals with maintained fascicular architecture, secondary to compression by the anconeus muscle. This paper reviews imaging findings of ulnar neuropathy secondary to accessory anconeus muscle and explains the importance of MRI imaging for accurate diagnosis. Knowing MRI imaging is vital in the modern imaging era for accurate diagnosis.