• Philipp Bäumer, Markus Weiler, Martin Bendszus, and Mirko Pham.
• From the Departments of Neuroradiology (P.B., M.B., M.P.) and Neurology (M.W.), Heidelberg University Hospital, Germany. philipp.baeumer@med.uni-heidelberg.de.
• Neurology. 2015 Apr 28; 84 (17): 1782-7.

ObjectivesTo investigate whether the human sciatic nerve might have a consistent somatotopic organization according to proximal fascicle input by spinal nerves.MethodsTwelve patients (55.3 ± 15.5 years) with confirmed lesions of either the L5 or S1 spinal nerve root underwent magnetic resonance neurography of sciatic nerve fascicles including thigh and knee levels (T2-weighted sequence with fat saturation, repetition time/echo time 7,552/52 milliseconds, voxel size 0.27 × 0.27 × 3.0 mm(3)). Twenty healthy subjects and 12 additional patients with an established diagnosis of peripheral polyneuropathy served as 2 separate age- and sex-matched control groups. Two blinded readers assessed patients and controls for presence of distinct lesion patterns. Spatial maps of normalized T2 signal were rendered after segmentation and coregistration of sciatic nerve voxels to detect fascicle lesion patterns.ResultsA clear somatotopic distribution of nerve fascicles was observed on cross-sections along the entire course of the sciatic nerve and was distinct between patients with L5 and those with S1 lesions. Fascicles emerging from L5 were ordered in anterolateral positions within sciatic nerve cross-sections, while fascicles emerging from S1 appeared posteromedially. Visual assessment discriminated these somatotopic lesions in all cases from both healthy and polyneuropathy controls.ConclusionA distinct pattern of somatotopy was identified within the sciatic nerve according to proximal fascicle input by L5 and S1 spinal nerves. Knowledge of human nerve somatotopy may have clinically useful implications in imaging-aided diagnosis of neuropathies.© 2015 American Academy of Neurology.

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