Primary intraosseous meningioma of the parasagittal region with continuous transcalvarial progression: illustrative case

BACKGROUND: Primary intraosseous meningioma (PIM) is a rare subtype of extradural meningioma arising within the cranial bones. Distinguishing true PIM from conventional meningioma with secondary osseous involvement remains challenging, and pathological evidence demonstrating continuous transcalvarial tumor involvement is rarely documented. OBSERVATIONS: A 74-year-old man receiving maintenance hemodialysis presented with progressive gait disturbance and cognitive decline. Serial imaging over 2.5 years demonstrated progression from a predominantly calvarial lesion with an associated extracranial scalp component to extensive intracranial extension, accompanied by chronic superior sagittal sinus (SSS) occlusion and marked collateral venous remodeling. Following preoperative embolization, subtotal resection was performed while preserving the chronically occluded SSS. Histopathological analysis revealed transitional meningioma (CNS WHO grade 1) with continuous infiltration of the subcutaneous tissue, calvarial marrow spaces, dura, and intradural compartment. Despite CNS WHO grade 1 histology, rapid local tumor recurrence measuring approximately 42 mm developed within 5 months after surgery. LESSONS: Although histological continuity alone cannot establish the site of origin or direction of tumor spread, the predominantly calvarial involvement on initial imaging and subsequent intracranial progression favored a primary intraosseous origin. Recognition of this growth pattern and associated chronic venous remodeling may facilitate accurate diagnosis, surgical planning, and postoperative surveillance. https://thejns.org/doi/10.3171/CASE26765.