Idiopathic Syringomyelia: A Systematic Scoping Review

Background: Idiopathic syringomyelia (IS) is defined by exclusion: an intramedullary fluid-filled cavity without Chiari malformation, spinal trauma, tumor, infection, or other identifiable cause. Growing evidence suggests IS is a progressively shrinking category as advanced imaging and intraoperative exploration uncover occult arachnoid or hydrodynamic substrates. To the best of our knowledge, no systematic reviews of the literature have been published on this topic. The authors aim to map operational definitions of IS, summarize proposed pathogenetic mechanisms, characterize diagnostic strategies and their yield, describe management approaches and outcomes, and identify pediatric-adult differences. Methods: A scoping review was conducted in accordance with PRISMA-ScR. PubMed and Scopus were searched from inception to May 2026. Eligible sources were original studies of any design addressing IS in pediatric or adult patients, in English. Studies on syringomyelia secondary to Chiari malformation, trauma, tumor, or infection were excluded. Data were extracted across five domains and synthesized narratively. Results: Eighteen studies (365 patients; five case reports, nine retrospective cohorts, two morphometric studies, one cine-MRI case-control, one technical note) were included. Operational definitions were markedly heterogeneous. Four pathogenetic mechanisms emerged: subarachnoid CSF obstruction with abnormal intramedullary pulse pressure, occult arachnoid pathology, posterior fossa morphometric variants overlapping with the Chiari spectrum, and persistent central canal as a developmental variant. In the four largest pediatric series (n = 214), 91-95% of children remained stable or improved on conservative management at up to 7-year follow-up, with no concordance between syrinx size change and clinical course. In symptomatic adults, targeted arachnoid lysis or web excision yielded clinical improvement in 87% of IS-occult arachnoid web patients; syringo-subarachnoid shunting was occasionally effective but risked neurological deterioration without prior substrate identification. Conclusions: The idiopathic label reflects the current limits of diagnostic investigation rather than a fixed nosological entity, since occult arachnoid or hydrodynamic substrates are identified in most adult IS cases when advanced imaging and intraoperative exploration are systematically deployed. Pathogenesis converges on a unified model of subarachnoid CSF obstruction generating abnormal intramedullary pulse pressure. Management should be driven by clinical, not radiological, evolution: arachnolysis or web excision is the primary strategy when an operable substrate is identified, while conservative management remains best supported in clinically stable patients, particularly children.