Fascicular torsions of the anterior and posterior interosseous nerve in 4 cases: neuroimaging methods to improve diagnosis

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Diagnosis of spontaneous fascicular nerve torsions is difficult and often delayed until surgical exploration is performed. This case series raises awareness of peripheral nerve torsions and will facilitate an earlier diagnosis by using nerve ultrasound (NUS) and magnetic resonance neurography (MRN). Four patients with previously ambiguous upper-extremity mononeuropathies underwent NUS and 3T MRN. Neuroimaging detected proximal torsions of the anterior and posterior interosseous nerve fascicles within median or radial nerve trunks in all patients. In NUS, most cases presented with a thickening of affected nerve fascicles, followed by an abrupt caliber decrease, leading to the pathognomonic sausage-like configuration. MRN showed T2-weighted hyperintense signal alterations of fascicles at and distal to the torsion site, and directly visualized the distorted nerves. Three patients had favorable outcomes after being transferred to emergency surgical intervention, while 1 patient with existing chronic muscle atrophy was no longer eligible for surgery. NUS and MRN are complementary diagnostic methods, and both can detect nerve torsions on a fascicular level. Neuroimaging is indispensable for diagnosing fascicular nerve torsions, and should be applied in all unclear cases of mononeuropathy to determine the diagnosis and if necessary, to guide surgical therapies, as only timely interventions enable favorable outcomes.

ABBREVIATIONS AIN = anterior interosseous nerve; EMG = electromyography; MRN = magnetic resonance neurography; NCS = nerve conduction studies; NUS = nerve ultrasound; PIN = posterior interosseous nerve.

Article Information

Correspondence Jennifer Kollmer: Heidelberg University Hospital, Heidelberg, Germany. jennifer.kollmer@med.uni-heidelberg.de.

INCLUDE WHEN CITING Published online May 24, 2019; DOI: 10.3171/2019.3.JNS183302.

Disclosures Dr. Kollmer received a research grant from Alnylam Pharmaceuticals, the Olympia Morata grant from the Medical Faculty of the University of Heidelberg, personal fees from Pfizer and Alnylam, financial support for conference attendance from Pfizer and the Amyloidosis Foundation, and honoraria for consultancy from Akcea Therapeutics. Prof. Bendszus received grants from the German Research Foundation (SFB 1118), Hopp Foundation, Novartis, European Union, Medtronic, Stryker, Siemens, Guerbet, and Codman; received honoraria for consultancy from BBraun, Roche, Boehringer, Ingelheim, Guerbet, Codman, and Vascular Dynamics; and received payments for lectures from Novartis, Guerbet, Codman, Bayer, Teva, and Roche.

© AANS, except where prohibited by US copyright law.

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    AIN torsion. Case 1. Axial (A) and coronal (B) MRN (high-resolution T2-weighted turbo spin echo sequence with spectral fat-saturation) at the level of the upper arm revealed a marked caliber and T2-weighted signal increase in several AIN fascicles within the median nerve at and distal to the torsion (arrowhead, A), as well as a typical focal decrease in nerve caliber directly at the torsion site (arrowhead, B). Note the normal T2-weighted signal of unaffected adjacent fascicles (arrow) within the same nerve (A). Case 2. MRN in the axial direction (high-resolution T2-weighted turbo spin echo sequence with spectral fat-saturation) revealed a marked increase of caliber and T2-weighted signal within several twisted AIN fascicles (arrowhead, C) next to unaffected median nerve fascicles with normal T2-weighted signal and caliber (arrow, C). In NUS, the torsion presented with a blurred sausage-like configuration (arrowhead, D). In the same patient, the surgical setting is shown directly after opening of the epineurium (E), and after careful preparation of the affected AIN fascicle (F). Here, a torsion could be confirmed (arrowheads) and was found at the exact anatomical location that was identified by MRN and NUS. Figure is available in color online only.

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    PIN torsion and neuroborreliosis in case 3. For illustration purposes, a 3D TRUFI (true fast imaging with steady-state free precession) sequence with coronal reformations, which was optimized for imaging of peripheral nerves and provided a high contrast and spatial resolution, was additionally acquired in this patient (A). It enabled visualization of the torsion of PIN fascicles within the radial nerve at the upper arm by showing the twisted fascicles with a typical focal caliber decrease (arrowhead, A). A clear sausage-like configuration of the lesion could be observed in NUS (arrowhead, B). However, additional multifocal T2-weighted hyperintense lesions of the radial, median, and ulnar nerves (arrows) could be detected by MRN (high-resolution T2-weighted turbo spin echo sequence with spectral fat-saturation; C). The fascicular PIN torsion (arrowhead) is shown during surgical neurolysis and detorsion (D). Figure is available in color online only.

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    PIN torsion in case 4. PIN fascicles with the pathognomonic sausage-like appearance in NUS can be seen at two different locations in close proximity to each other (arrowheads, upper). During surgical intervention, fascicular torsions could be validated at both locations (arrowheads, lower). Arrowheads indicate the focal constrictions. Figure is available in color online only.

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