title: Anterior interosseous nerve syndrome: fascicular motor lesions of median nerve trunk.
abstract: OBJECTIVE
  We sought to determine lesion sites and spatial lesion patterns in spontaneous anterior interosseous nerve syndrome (AINS) with high-resolution magnetic resonance neurography (MRN).
  
  
  METHODS
  In 20 patients with AINS and 20 age- and sex-matched controls, MRN of median nerve fascicles was performed at 3T with large longitudinal anatomical coverage (upper arm/elbow/forearm): 135 contiguous axial slices (T2-weighted: echo time/repetition time 52/7,020 ms, time of acquisition: 15 minutes 48 seconds, in-plane resolution: 0.25 × 0.25 mm). Lesion classification was performed by visual inspection and by quantitative analysis of normalized T2 signal after segmentation of median nerve voxels.
  
  
  RESULTS
  In all patients and no controls, T2 lesions of individual fascicles were observed within upper arm median nerve trunk and strictly followed a somatotopic/internal topography: affected were those motor fascicles that will form the anterior interosseous nerve further distally while other fascicles were spared. Predominant lesion focus was at a mean distance of 14.6 ± 5.4 cm proximal to the humeroradial joint. Discriminative power of quantitative T2 signal analysis and of qualitative lesion rating was high, with 100% sensitivity and 100% specificity (p < 0.0001). Fascicular T2 lesion patterns were rated as multifocal (n = 17), monofocal (n = 2), or indeterminate (n = 1) by 2 independent observers with strong agreement (kappa = 0.83).
  
  
  CONCLUSIONS
  It has been difficult to prove the existence of fascicular/partial nerve lesions in spontaneous neuropathies using clinical and electrophysiologic findings. With MRN, fascicular lesions with strict somatotopic organization were observed in upper arm median nerve trunks of patients with AINS. Our data strongly support that AINS in the majority of cases is not a surgically treatable entrapment neuropathy but a multifocal mononeuropathy selectively involving, within the main trunk of the median nerve, the motor fascicles that continue distally to form the anterior interosseous nerve.
authors.affiliation: From the Departments of Neuroradiology (M.P., P.B., M.B.) and Neurology (H.-M.M., M.W.), Heidelberg University Hospital; Clinical Cooperation Unit Neurooncology (M.W.), German Cancer Research Center (DKFZ), Heidelberg; Department of Neurology (J.S.), RWTH University Hospital Aachen; and Center for Neurology and Clinical Neurophysiology Neuer Wall (H.K.), Hamburg, Germany.
authors.forename: Mirko
authors.initials: M
authors.lastname: Pham
authors.forename: Philipp
authors.initials: P
authors.lastname: Bäumer
authors.forename: Hans-Michael
authors.initials: HM
authors.lastname: Meinck
authors.forename: Johannes
authors.initials: J
authors.lastname: Schiefer
authors.forename: Markus
authors.initials: M
authors.lastname: Weiler
authors.forename: Martin
authors.initials: M
authors.lastname: Bendszus
authors.forename: Henrich
authors.initials: H
authors.lastname: Kele
mesh_terms: D000328:Adult; D001132:Arm / Q000294:innervation*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods; D008297:Male; D008475:Median Nerve / Q000473:pathology*; D008875:Middle Aged; D016472:Motor Neuron Disease / Q000175:diagnosis / Q000473:pathology / Q000503:physiopathology; D010523:Peripheral Nervous System Diseases / Q000175:diagnosis* / Q000473:pathology* / Q000503:physiopathology; D013577:Syndrome