Diffusion Tensor Imaging for Diagnosing Root Avulsions in Traumatic Adult Brachial Plexus Injuries: A Proof-of-Concept Study
Ryckie G Wade, MBBS MSc MClinEd MRCS FHEA1, Steven F Tanner, BSc MSc PhD2, Irvin Teh, BE MBiomedE PhD1, John P Ridgway, BSc MSc PhD2, David Shelley, BSc PGCert MSc1, Brian Chaka, BSc PgDip MSc2, James J Rankine, MBChB MRCP MRad FRCR MD3, Gustav Andersson, MD PhD4, Mikael Wiberg, MD PhD5 and Grainne Bourke, MB BCh BAO FRCSI FRCS(Plast)6, (1)University of Leeds, Leeds, United Kingdom, (2)Leeds Biomedical Research Centre, Leeds, United Kingdom, (3)Leeds Teaching Hospitals, Leeds, United Kingdom, (4)Umeå University, Umeå, Sweden, (5)Umea University, Umea, Sweden, (6)Leeds Teaching Hospitals Trust, Leeds, United Kingdom
Diffusion Tensor Imaging for Diagnosing Brachial Plexus Injuries: A Proof of Concept Study
Background: Cross-sectional MRI has modest diagnostic accuracy for diagnosing traumatic brachial plexus root avulsions. Consequently, patients either undergo major exploratory surgery or months of surveillance to determine if and what nerve reconstruction is needed. This study aimed to develop a diffusion tensor imaging (DTI) protocol at 3 Tesla to visualise normal roots and identify traumatic root avulsions of the brachial plexus.
Methods: Seven healthy adults and twelve adults with known (operatively explored) unilateral traumatic brachial plexus root avulsions were scanned. DTI was acquired using a single-shot echo-planar imaging sequence at 3 Tesla. The brachial plexus was visualised by deterministic tractography. Fractional anisotropy (FA) and mean diffusivity (MD) were calculated for injured and avulsed roots in the lateral recesses of the vertebral foramen.
Results: DTI tractography reconstructs the normal brachial plexus and root avulsions with high fidelity (Figures 1 and 2, respectively). Compared to healthy nerves roots, the FA of avulsed nerve roots was lower (mean difference 0.1 [95% CI 0.07, 0.13]; p<0.001) and the MD was greater (mean difference 0.32 x10-3 mm2/s [95% CI 0.11, 0.53]; p<0.001) as shown in Figures 3 and 4, respectively. Deterministic tractography reconstructed both normal roots and root avulsions of the brachial plexus; the negative-predictive value for at least one root avulsion was 100% (95% CI 78, 100).
Conclusions: DTI might help visualise both normal and injured roots of the brachial plexus aided by tractography. The precision of this technique and how it relates to neural microstructure will be further investigated in a prospective diagnostic accuracy study of patients with acute brachial plexus injuries.
Figure 1. Diffusion tensor imaging tractography of the cervical cord and brachial plexus in four healthy volunteers.
Figure 2. Diffusion tensor imaging tractography of the cervical cord and brachial plexus in four patients with known root avulsions. Top left) Isolated left C7 avulsion, top right) Left C7, C8 and T1 avulsions, lower left) Right C5, C6 and C7 avulsions and lower right) Left panplexus avulsion.
Figure 3. The mean diffusivity of the lateral recess of the vertebral foramen, housing either normal or avulsed C5-T1 nerve roots.
Figure 4. The fractional anisotropy of the lateral recess of the vertebral foramen, housing either normal or avulsed C5-T1 nerve roots.
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