Hyperostotic en Plaque Meningioma Mimicking Fibrous Dysplasia of the Temporal Bone

Background: Meningiomas are the most common nonglial, primary intracranial tumor. They arise from the meninges and are usually described based on their specific site of origin. An en plaque lesion represents a distinct subtype characterized by a sheet-like appearance, which differs from the globular appearance of the more common en masse tumors. For unclear reasons, en plaque meningiomas are more likely to provoke adjacent bony hyperostosis. We present the case of a patient with a hyperostosis reaction provoked by an en plaque meningioma, which had previously been diagnosed as fibrous dysplasia.

Case Presentation: A 42-year-old female presented for evaluation and treatment of a firm, enlarging temporal-parietal mass. In the years leading up to her presentation at our institution, the mass had been evaluated with CT and was thought to represent fibrous dysplasia. However, as it grew, it became associated with headaches, disequilibrium, and nausea. On clinical examination, the patient was noted to have a bony protuberance that appeared to arise from the squamosal portion of the left temporal bone. In addition, a left-sided middle ear effusion, ataxia, and dysmetria were identified. Cranial nerve function, extremity motor strength, and sensation were intact. Audiometry revealed a left-sided conductive hearing loss. A CT was reviewed, which revealed hyperostotic changes of the temporal, parietal, and occipital skull. A rim of subdural calcification was identified, and the structures of the otic capsule appeared unaffected. A contrast-enhanced MRI revealed an extra axial enhancing mass in the left parietal and temporal lobes extending into the posterior fossa and along the tentorium associated with hyperostosis. Significant mass effect and edema were identified in the left cerebellar hemisphere, temporal lobe, parietal lobe, and brain stem. On the basis of these findings, the diagnosis of an en plaque meningioma was made. The patient was taken to the operating room, where the hyperostotic bone was removed and a cranial nerve-sparing near-total microsurgical resection with preservation of vein of Labbé, which was encased within the tumor. Histopathologic analysis of the resected tumor identified a World Health Organization grade I meningioma. At 7 months of postoperative follow-up, the patient remains neurologically intact and will be followed with serial MRI scans.

Conclusion: The diagnosis and management of extensive en plaque meningiomas can be difficult, especially in the setting of extensive hyperostosis. While CT is excellent for visualization of the hyperostosis, MRI is necessary to identify the intracranial tumor, with axial postcontrast fat suppression T1-weighted MRI being particularly helpful.