Acute radial nerve entrapment at the spiral groove: detection by DTI-based neurography.

OBJECTIVES: This study evaluated the potential of three-tesla diffusion tensor imaging (DTI) and tractography to detect changes of the radial (RN) and median (MN) nerves during transient upper arm compression by a silicon ring tourniquet.

METHODS: Axial T2-weighted and DTI sequences (b = 700 s/mm(2), 16 gradient encoding directions) of 13 healthy volunteers were obtained. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of the MN and RN were measured at the spiral groove and further visualized in 3D by deterministic tractography (thresholds: FA = .15, angle change = 27°).

RESULTS: Local/lesional RN FA values increased (p = 0.001) and ADC values decreased (p = 0.02) during a 20-min upper arm compression, whereas no significant FA (p = 0.49) or ADC (p = 0.73) changes of the MN were detected. There were no T2-w nerve signal changes or alterations of nerve trajectories in 3D.

CONCLUSIONS: Acute nerve compression of the RN leads to changes of its three-tesla DTI metrics. Peripheral nerve DTI provides non-invasive insights into the "selective" vulnerability of the RN at the spiral groove.

KEY POINTS: • DTI-based neurography detects nerve changes during acute nerve compression. • Compression leads to a transient increase in local radial nerve FA values. • DTI provides insights into radial nerve vulnerability at the spiral groove.