Introduction In this study we tested the hypothesis that fascicular constrictions
(FCs) of the median nerve proximal to the elbow joint characterize anterior interosseous
nerve syndrome (AINS). Methods Magnetic resonance neurography (MRN) and ultrasound
(US) examinations were evaluated in 45 patients with clinically suspected AINS. All
22 patients at site 1 underwent MRN and 8 underwent US; all 23 patients at site 2
underwent US. Results Median nerve FCs were identified in all MRN cases; FCs and/or
fascicular enlargements were identified in 88% of US cases. Most FCs were in the mediannerve
posterior/posteromedial region and were proximal to the elbow joint line (mean distance:
MRN, 5.4 cm; US, 7.5 cm), with the exception of a single FC (located 1 cm distal).
No extrinsic compression of median or anterior interosseous nerves was identified
in the arm or forearm. Discussion AINS is a noncompressive neuropathy characterized
by median nerve FCs in the arm.
