Superficial siderosis caused by a tiny dural defect localized by an isodense crossing point on CT myelography: illustrative case

BACKGROUND: Superficial siderosis (SS) is a rare disease characterized by hemosiderin deposition on the brain or spinal surface, potentially leading to cerebellar ataxia, hearing loss, and dementia. For SS caused by spinal dural defects, surgical closure prevents clinical progression; however, precise localization of very small defects remains challenging with conventional imaging modalities. OBSERVATIONS: A 47-year-old male with progressive SS was diagnosed with CSF leakage from a ventral spinal dural defect, but the lesion could not be localized clearly by MRI. CT myelography focusing on the difference in contrast enhancement between true and false lumens revealed an isodense crossing point at C7-T1, which corresponded to a 1 × 2-mm ventral dural defect identified intraoperatively, resulting in successful surgical repair. The postoperative course was uneventful, and follow-up MRI revealed complete absence of a false lumen. LESSONS: Identifying an isodense crossing point between intradural and extradural spaces on CT myelography may help localize tiny dural defects in patients with SS. https://thejns.org/doi/10.3171/CASE26471.