American Society for Peripheral Nerve

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MRI Evaluation of Nerve Root Avulsion in Neonatal Brachial Plexus Palsy, Understanding the Presence of Isolated Dorsal/Ventral Rootlet Disruption
Brandon W Smith, MD, MS; Hemant Parmar, MD; Kate Wan-Chu Chang, MA, MS; Lynda Yang, MD, PhD
University of Michigan, Ann Arbor, MI

The evaluation, treatment, and prognosis of neonatal brachial plexus palsy continues to have many areas of debate, including the use of ancillary testing. Given the continued improvement in radiographic imaging, it is important to revisit its utility in our field. Nerve root avulsions have historically been identified by the presence of pseudomeningoceles or visible ruptures of nerve rootlets from the spinal cord. The "all or none" definition of nerve root avulsions has many implications in the understanding and management of NBPP. This study examined the ability of high resolution MRI to more specifically define the anatomy of nerve root avulsions by individually examining the dorsal and ventral rootlets at each level as they exit the spinal cord.

This is a retrospective review of patients that had undergone a brachial plexus protocol MRI for clinical evaluation of NBPP. Each MRI was independently reviewed by a board-certified neuro-radiologist that was blinded both the established diagnosis/surgical findings and laterality. Each dorsal and ventral nerve rootlet from C5-T1 was evaluated from the spinal cord to its exit in the neuroforamen. Each rootlet was classified as avulsed, intact, or undeterminable.

61 infants underwent the brachial plexus protocol MRI from 2010 to 2018. All infants were included in this study. 610 individual rootlets were analyzed in total. There were 41 avulsed nerve rootlets in this cohort. There were 29 (70.7%) total nerve root avulsions involving the ventral and dorsal rootlet, and 12 (29.3%) isolated ventral or isolated dorsal rootlet avulsions. Isolated rootlet avulsions were present in 75%, 30%, 29.4%, 11.1%, and 0% of the avulsions at C5, C6, C7, C8, and T1, respectively. There were 5 (12.2%) isolated ventral rootlet avulsions and 7 (17.1%) isolated dorsal rootlet avulsions. There were 11 (1.8%) rootlets that were undeterminable.

A closer look at nerve root avulsions with MRI demonstrates a significant prevalence of isolated nerve rootlet disruption, approximately 30%. This finding implies that nerve roots previously labeled as "avulsed" but with only isolated dorsal (sensory) rootlet avulsion can yet provide donor fascicles in reconstruction strategies. We also show that a majority, 98.2%, of the rootlets can be clearly visualized with MR. These findings may significantly impact our clinical understanding of neonatal brachial plexus injury and its treatment.

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