Thickened hyperechoic outer epineurium, a sonographic sign suggesting snapping ulnar nerve syndrome?

PURPOSE

Snapping ulnar nerve syndrome (dislocation of the ulnar nerve over the medial epicondyle) is one of many causes of ulnar neuropathy at the elbow. This preliminary study was performed to search for sonographic signs suggesting the presence of this condition.

METHODS AND MATERIALS

We retrospectively investigated 11 patients with snapping ulnar nerve syndrome (SNAP) in comparison with an age-matched group of 20 patients with idiopathic cubital tunnel syndrome (SNU). Patients were grouped according to the presence of paretic or merely sensory deficits. Nerve cross section area (CSA) and thickness of outer epineurium (ET) was measured and correlated with neurological findings. Statistical differences were evaluated with the Mann-Whitney U-Test.

RESULTS

5 SNAP (10 SNU) patients had sensory symptoms only, 6 SNAP (10 SNU) patients had paretic deficits. CSA in sensory SNU was 0.14 cm(2), in paretic SNU 0.19 cm(2), in sensory SNAP 0.15 cm(2) and in paretic SNAP 0.14 cm(2). ET in sensory SNU was 0.85 mm, 0.8 mm in paretic SNU, 1.05 mm in sensory SNAP and 1.1 in paretic SNAP. Differences in CSA were not significant depending on symptoms or group, differences in ET were not significant depending on symptoms but on group (SNAP versus SNU) at α = 0.05.

CONCLUSION

A thickened, hyperechoic outer epineurium in a patient with ulnar neuropathy at the elbow might be a statistically significant differential feature of snapping ulnar nerve syndrome and should be involved in a further functional sonographic evaluation during flexion/extension of the elbow.