The Epidemiology of Syringomyelia and Associated Conditions: A Literature Review

Background/Objectives: Syringomyelia is an intramedullary, fluid-filled cavity that expands the spinal cord, usually secondary to impaired cerebrospinal fluid (CSF) flow at the craniovertebral junction or spinal canal, or to spinal cord tethering. Its epidemiology is difficult to define because related entities—including hydromyelia, persistent or dilated central canal, slit-like cavities, presyrinx, postsyrinx, myelomalacia, glioependymal cysts, and cystic tumors—are inconsistently classified. This review evaluated syringomyelia classification and prevalence in relation to associated disorders and diagnostic criteria. Methods: A MEDLINE/PubMed and Google Scholar search was performed through May 2026 using terms related to syringomyelia, hydromyelia, central canal dilatation, slit-like cavities, presyrinx/postsyrinx states, Chiari malformations, prevalence, incidence, and classification. Eligible sources included clinical studies, cohort and case–control studies, family/genetic studies, reviews, historical articles, and book chapters. Duplicates and inaccessible full-text sources were excluded. Results: Since MRI became the diagnostic standard, syringomyelia has been detected earlier and more often, including in oligosymptomatic and asymptomatic patients. MRI has also improved identification of associated conditions, particularly Chiari malformation type 1 (CM1), basilar invagination, spinal pathology, and CSF pathway obstruction. Reported MRI-era prevalence varies substantially across populations, from 1.94 per 100,000 in Japan to 4.84 per 100,000 in Northwestern Italy and 8.2 per 100,000 in New Zealand, with higher rates in selected Russian regions with familial or ethnic clustering of CM1. CM1 is consistently the most common associated condition. However, prevalence estimates are affected by whether hydromyelia, persistent central canal variants, slit-like cavities, and presumed idiopathic syringomyelia are included. Apparent idiopathic cases may reflect occult CSF obstruction, arachnoid adhesions, Chiari type 0, or spinal canal abnormalities. Conclusions: Syringomyelia prevalence varies by geography, ethnicity, associated conditions, imaging era, and diagnostic definitions. Standardized clinicoradiological criteria are needed to distinguish true syringomyelia from related cavity conditions and improve epidemiological accuracy.