Primary Extracranial Meningioma of the Sphenoid Bone Without Dural Attachment Presenting With Multicompartmental Extension: A Case Report

Primary extracranial meningiomas are rare tumors that arise outside the cranial cavity without continuity with intracranial structures, and their preoperative diagnosis is often challenging. We report a rare case of a primary extracranial meningioma centered on the sphenoid bone with multicompartmental extension. A 53-year-old woman presented with a gradually enlarging mass in the left temporal region. Imaging revealed a well-defined lesion extending from the sphenoid sinus to the lateral orbit and temporal region. Computed tomography (CT) demonstrated bone thinning and remodeling without destructive changes. Magnetic resonance imaging showed homogeneous contrast enhancement without parenchymal invasion or peritumoral edema. Notably, iodine-123 N-isopropyl-p-iodoamphetamine (¹²³I-IMP) single-photon emission CT (SPECT) showed no significant tracer uptake, and three-dimensional CT angiography revealed no abnormal tumor vascularity. The tumor was resected via a frontotemporal craniotomy. No continuity with the dura mater was identified intraoperatively. Histopathological examination demonstrated whorl formation and numerous psammoma bodies, and immunohistochemical findings confirmed a World Health Organization grade 1 transitional meningioma with a low Ki-67 labeling index. Tumor infiltration was observed within both trabecular bone and, in a separate specimen, the temporalis muscle, supporting an extracranial origin. This case highlights that primary extracranial meningioma should be considered in the differential diagnosis of skull base lesions showing non-destructive bony remodeling, homogeneous enhancement, absence of tracer uptake on ¹²³I-IMP SPECT, and lack of dural continuity. For accurate diagnosis, integration of imaging, intraoperative findings, and histopathology is essential.