Intrasinus solitary fibrous tumor mimicking cerebral venous sinus thrombosis: A case report.

Solitary fibrous tumors (SFTs), encompassing lesions previously classified as hemangiopericytoma, are rare mesenchymal neoplasms. Intracranial SFTs confined to the dural venous sinus are extremely rare and may mimic cerebral venous sinus thrombosis (CVST). A 76-year-old man presented with impaired consciousness and an elevated D-dimer level. Non-contrast computed tomography and magnetic resonance imaging (MRI) revealed an intraluminal lesion within the posterior superior sagittal sinus. The lesion exhibited mild T2-weighted hyperintensity, without internal flow voids or associated mass effect. CVST was suspected, and anticoagulation therapy was initiated. Imaging follow-up was discontinued after symptomatic improvement. One year later, the patient re-presented with a headache. MRI demonstrated marked enlargement of the lesion, with extension beyond the dura into the adjacent brain parenchyma. Biopsy and subsequent surgical resection confirmed a World Health Organization Central Nervous System grade 1 SFT. Small intrasinus SFTs may closely mimic CVST; therefore, careful imaging follow-up is essential for accurate differentiation.