Perineural spread to the brachial plexus: a focused review of proposed mechanisms and described pathologies

[[[ Background: ]]] Perineural spread (PNS) is an emerging mechanism for progressive, non-traumatic brachial plexopathy. We aim to summarize the pathologies (tumor and infection) shown to have spread along or to the brachial plexus, and identify the proposed mechanisms of perineural spread. [[[ Methods: ]]] A focused review of the literature was performed pertaining to pathologies with identified perineural spread to the brachial plexus. [[[ Results: ]]] We summarized pathologies currently reported to have PNS in the brachial plexus and offer a structure for understanding and describing these pathologies with respect to their interaction with the peripheral nervous system. [[[ Conclusions: ]]] Perineural spread is an underrepresented entity in the literature, especially regarding the brachial plexus. It can occur via a primary or secondary mechanism based on the anatomy, and understanding this mechanism helps to support biopsies of sacrificial nerve contributions, leading to more effective and timely treatment plans for patients.