Diffusion Tensor Imaging for Diagnosing Root Avulsion in Adults with Acute Trauma Brachial Plexus Injuries: A Pilot Study
Ryckie George Wade, MBBS MSc MClinEd MRCS FHEA GradStat PhD1, David Shelley, BSc PGCert MSc2, Sven Plein, MD PhD FRCP FESC2, Robert D Bains, MBChB BSc FRCS(Plast)3, James Bedford, MSc FRCS(Plast) BrDipHandSurg4, Lucy Homer Newton, MbChB(Hons) MRes MRCS4, Chye Yew Ng, MD5, Yemisi Takwoingi, DVM MSc PhD6, Irvin Teh, BE MBiomedE PhD2 and Gráinne Bourke, MB BCh BAO FRCSI FRCS(Plast) PhD3, 1Department of Plastic and Reconstructive Surgery, University of Leeds, Leeds, United Kingdom, 2University of Leeds, Leeds, United Kingdom, 3Leeds Teaching Hospitals NHS Trust, Leeds, United Kingdom, 4Manchester University NHS Foundation Trust, Manchester, United Kingdom, 5Wrightington Hospital, Wigan, United Kingdom, 6University of Birmingham, Birmingham, England, United Kingdom
Introduction: Root avulsion in traumatic brachial plexus injury (tBPI) is common and early nerve transfers are associated with better outcomes. Current morphological-based MRI sequences has modest diagnostic accuracy for root avulsions. Diffusion tensor MRI (DTI) characterises tissue microstructure and generates proxy measures of nerve ‘health’ which are sensitive to myelination, axon diameter, density and organisation (Figure 1). The prospective multicentre cohort study investigated DTI for detecting root avulsion in adults with acute tBPI.
Methods: Using a Siemens 3T system, patients underwent DTI once clinically stable. Fractional anisotropy (FA) and radial diffusivity (RD) were extracted from bilateral C5-T1 roots. We confirmed root avulsion by surgical exploration. Injured but in-continuity roots were those either confirmed as intact at exploration or those which clinically recovered function between the time of scanning and before the planned exploration. The spinal nerve root was the unit of analysis. Comparisons were made between root avulsions, in-continuity roots (whether through spontaneous recovery or operatively determined) and the contralateral uninjured roots, using linear methods and 95% confidence intervals (CI) were computed.
Results: 14 males with tBPI (mean age 44 years, SD 14) were scanned at a median of 23 days post-injury (IQR 7-54). Of these, 7 underwent exploration at a mean of 37 days (SD 20) whilst 7 recovered spontaneously. Diffusion was more isotropic in avulsed roots (Figure 2); root avulsions had 12% lower FA than injured but in-continuity roots (CI 5-19) and 14% lower FA (CI 7-21) than the contralateral brachial plexus roots. Similarly, avulsed roots had higher radial diffusivity (Figure 3) than injured in-continuity roots (mean difference 0.30 x10-3 mm2/s [CI 0.01-0.60]) and contralateral uninjured roots (mean difference 0.36 x10-3 mm2/s [CI 0.7-0.64]).
Conclusions: Diffusion tensor imaging appears to be sensitive to the early microstructural changes of avulsed roots in adults with tBPI. This test may augment the current MRI sequences to improve its overall diagnostic accuracy and therefore, better identify patients who may benefit from early exploration and reconstruction.
Figure 1. A schematic showing the diffusion of water within a normal (blue), abnormal (yellow) and injured (red) nerve.
Figure 2. Diffusion within the stump of a root avulsion is more isotropic than in-continuity injuries or the contralateral normal roots.
Figure 3. Diffusion perpendicular to the axis of the nerve (radially) was 27% higher in the distal stump of avulsed roots than in-continuity injuries and 34% higher than the contralateral normal roots.
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