Intracranial subdural osteoma: a rare benign tumor that can be differentiated from other calcified intracranial lesions utilizing MR imaging.

We report the magnetic resonance (MR) imaging characteristics of subdural osteoma and other benign calcified intracranial lesions to highlight imaging features that differentiate between these disease entities. A 63-year-old woman presented with progressively altered mental status. Non-contrast CT demonstrated a densely calcified right middle cranial fossa extra-axial mass. MR imaging of the lesion demonstrated T1 and T2 hypointensity without evidence of contrast enhancement, parenchymal abnormality, or connection to adjacent venous structures. Diffusion weighted imaging demonstrated markedly decreased signal intensity and artificially reduced diffusion on apparent diffusion coefficient map. Histologically, the tumor was predominantly composed of lamellar bone and small fragments of residual dura consistent with subdural osteoma. This case demonstrates that radiological examination can provide additional insight into the origin of intracranial osteomas (extradural versus subdural versus sinonasal) and help distinguish from other diagnostic considerations including benign meningeal ossification and calcified meningioma prior to surgical resection.