Imaging description

Meningiomas are common benign masses that are easily recognized on the basis of their typical dural-based location. About 1–2% of menigiomas arise from extradural locations and pose a diagnostic challenge [1]. The most common extradural location is the calvarium (Fig. 33.1) [3–5]. Primary intraosseous meningiomas (PIMs) require differentiation from other bone lesions, ranging from benign process such as fibrous dysplasia to highly malignant masses such as osteosarcoma [2]. Although initially presumed to arise from meningothelial cells trapped in sutures or fracture lines, only 8% of the calvarial meningiomas are found along the cranial sutures [4] and only 15% of the PIMs have a history of trauma to the head [3]. They probably arise from multipotent mesenchymal cell precursors, likely as a reaction to an unidentified stimulus [4].

Most of the PIMs tend to present with hyperostosis, but they may present with osteolytic or mixed appearance on CT scans, generating a differential diagnosis depending on distinguishing subtype [6]. On MRI there is always soft tissue enhancement adjacent to the bone lesion. Soft tissue enhancement may be intra- and/or extracranial, and it may range from mild dural thickening to sizable masses. It may be difficult to distinguish an intradural plaque such as meningioma with associated reactive hyperostosis from a true PIM with imaging (Fig. 33.2). Most PIMs are benign, although osteolytic skull lesions and extracranial soft tissue masses are associated with more aggressive histologic subtypes [4,6].