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To The Editor: Syringomyelia is a disorder characterized by fluid accumulation in the spinal cord. Despite almost a century of research and numerous theories, its pathophysiology remains elusive. In the Journal of Neurosurgery: Spine, Hemley et al.3 published an article (Hemley SJ, Bilston LE, Cheng S, et al: Aquaporin-4 expression and blood–spinal cord barrier permeability in canalicular syringomyelia. Laboratory investigation. J Neurosurg Spine 17:602–612, December 2012). Blood–spinal cord barrier (BSCB) disruption was demonstrated by means of intravenously injected horseradish peroxidase leakage in the perivascular space. Aquaporin-4 (AQP4) and