Elbow nerves: MR findings in 60 asymptomatic subjects--normal anatomy, variants, and pitfalls.

PURPOSE: To prospectively evaluate the signal intensity (SI), course, and diameter of elbow nerves and to identify anatomic variants that are potentially associated with nerve compression syndromes on magnetic resonance (MR) images of asymptomatic elbows.
MATERIALS AND METHODS: This study was approved by the institutional review board. Informed consent was obtained from each volunteer. Sixty subjects with asymptomatic elbows (age range, 22.4-51.7 years; median age, 32.8 years) underwent MR imaging. Increased SI compared with surrounding muscles on fluid-sensitive MR images, anatomic course, anatomic nerve and muscle variants potentially associated with nerve compression syndromes, and qualitative changes in nerve diameters were evaluated. Quantitative data on the shortest and longest nerve diameters were obtained.
RESULTS: Increased SI on fluid-sensitive MR images was seen in the ulnar nerve in 60% (36 of 60) of subjects but was never observed in the median and radial nerves. An atypical intermuscular course of the median nerve between the brachialis and pronator muscles was detected in 17% (10 of 60) of subjects. Ulnar nerve subluxation at the level of the cubital tunnel was seen in 2% (one of 60) of subjects; an anconeus epitrochlearis muscle, in 23% (14 of 60); and a hypertrophic leash of Henry, in 15% (nine of 60). Median nerve dimensions were 2.4 x 4.0 mm (range, 1.0-4.0 x 3.0-7.0 mm) for the ulnar nerve, 1.0 x 1.9 mm (range, 0.8-2.0 x 0.9-5.0 mm) for the radial nerve, and 3.0 x 5.4 mm (range, 1.0-5.0 x 3.0-9.0 mm) for the median nerve.
CONCLUSION: Increased SI of the ulnar nerve on fluid-sensitive images (60%), an atypical intermuscular course of the median nerve (17%), and an anconeus epitrochlearis muscle (23%) are common MR findings in asymptomatic elbows. (c) RSNA, 2009.