Embolization of CSF-venous fistula for syrinx resolution in acquired Chiari malformation: illustrative case.

backgroundChiari malformation type I (CM-I) shares some overlapping radiological and clinical features of spontaneous intracranial hypotension (SIH). Recent work has recognized CSF-venous fistula (CVF) as an underdiagnosed cause of SIH. The authors present a case of presumed CM-I with tonsillar descent and syrinx that progressed despite posterior fossa decompression (PFD), with subsequent diagnosis of SIH due to CVF. Treatment of the CVF by transvenous embolization rapidly improved intracranial brain sag with early syrinx reduction. OBSERVATIONS: Endovascular embolization of CVF produces durable improvements in brain sag and reduction in syrinx at 1 year, by alleviating the effects of the acquired Chiari and restoring CSF flow at the foramen magnum. Unrecognized SIH/spinal CSF leakage may account for some cases of failed syrinx improvement after PFD for CM-I. LESSONS: Patients presenting with tonsillar herniation and syringomyelia should have brain and spine imaging to assess for evidence of SIH. The presence of syrinx, although more common in CM-I, may occur in SIH. Persistent or worsening syringomyelia after PFD should prompt reassessment for possible SIH, including invasive CSF leak testing. Endovascular embolization of the CVF effectively treats SIH by restoring CSF homeostasis and reduces syrinx formation from acquired tonsillar herniation. https://thejns.org/doi/10.3171/CASE26202.