Syringomyelia: A Review Mudit Sharma, MD, Nicholas Coppa, MD, and Faheem A. Sandhu, MD, PhD Syringomyelia is a pathological entity characterized by spinal cord cavitation that often translates into a progressive clinical syndrome ranging from minimal to significant loss of neurological function. Although syringomyelia is often described in the context of a coex- isting Chiari malformation, it can be present in a wide spectrum of disease processes. In this article we present a review of the pathophysiology and treatment strategies in syrin- gomyelia. A classification system for this clinical entity is also outlined. Semin Spine Surg 18:180-184 © 2006 Elsevier Inc. All rights reserved. KEYWORDS syrinx, syringomyelia, hydromyelia, spinal cord cavitation, Chiari malformations S yringomyelia is a pathological entity characterized by spi- nal cord cavitation that often translates into a progressive clinical syndrome ranging from minimal to significant loss of neurological function. Its prevalence is 8.4 cases per 100,000 population with 21,000 Americans affected annually. 1 Al- though syringomyelia is often described in the context of a coexisting Chiari malformation, it can be present in a wide spectrum of disease processes. Advancements in neuroimag- ing have led to earlier diagnosis of syringomyelia. A syrinx can be an incidental finding. The definitive management in these cases is not clearly defined. Research efforts focused on the pathophysiological mechanisms of spinal cord cavitation will help to better understand the etiology and promote problem based treatment strategies. Terminology The term syringomyelia has been applied to any fluid-filled cavity within the spinal cord. Unfortunately, this term does not convey information about patterns of syrinx initiation, development or mechanism of progression, pathological as- sociation, or optimal treatment. Historically, “syringomyelia” refers to a chronic accumulation of fluid anywhere in the substance of the spinal cord. The term “hydromyelia” refers to a condition in which the central canal of the spinal cord communicates with the fourth ventricle and is distended with cerebrospinal fluid. The syringomyelic cavity in hydro- myelia is lined with ependymal cells, whereas a syrinx cavity is not. Spinal cord cavitations, according to Kyoshima and co- workers, can be categorized syringomyelic in accordance with the three following concepts: 1. Fluid composition: Spinal cord cavities either contain cerebrospinal fluid (CSF cavity) or some other protein- aceous fluid (non-CSF cavity). 2 2. Communication with the fourth ventricle: The term “communicating syringomyelia” refers to a fluid-filled distention of the central canal that communicates with the fourth ventricle. This is hydromyelia as defined above. If no communication with the fourth ventricle can be identified, the condition is termed “noncommu- nicating syringomyelia.” 2 3. Anatomical location: Cavitations that extend from di- lated central canals are lined by ependymal cells and contain cerebrospinal fluid. Otherwise, cavities origi- nate within the spinal cord parenchyma, lack an ependymal lining, and often contain fluid other than CSF. 2 We believe that most cavity fluid communicates to some extent, directly or indirectly, with CSF. Classification of Syringomyelia In an attempt to unify our understanding of the mechanisms of spinal cord cavitation and the histopathological changes that occur, Milhorat and coworkers established a disease- based classification system for syringomyelia with the aim of facilitating magnetic resonance imaging (MRI) interpretation and diagnosis, while providing a guide for optimal treat- ment. 3-5 Within this classification, there are four categories Department of Neurosurgery, Georgetown University Hospital, Washing- ton, DC. Address reprint requests to Faheem A. Sandhu, MD, PhD, Assistant Profes- sor, Department of Neurosurgery, Georgetown University Hospital, 7 PHC, 3800 Reservoir Road, Washington, DC 20007. E-mail: sandhuf@ georgetown.edu 180 1040-7383/06/$-see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1053/j.semss.2006.06.008