Intraosseous meningioma mimicking osteosarcoma

Abstract

Background: Predominantly intraosseous meningiomas are rare entities that include true primary intraosseous meningiomas (PIM), as well as meningiomas that may show extensive bone involvement, such as en plaque meningiomas. Different hypotheses have been proposed to decipher the origin of PIMs, such as ectopic arachnoid cap cell entrapment during birth or after trauma. Surgical resection is the treatment of choice of such lesions.

Case presentation: We present a case of a 65-year-old man with an enlarging mass in the parieto-occipital region that grew slowly and progressively over 13 years, following head trauma during a motor vehicle accident. One year prior to presentation, he started experiencing daily holocranial headaches and blurry vision. CT and MRI studies revealed a permeative midline calvarial lesion measuring 14 cm in greatest dimension with extensive periosteal reaction, extension into the subcutaneous soft tissues, subjacent dural thickening and intracranial extension with invasion of the superior sagittal sinus. The favored pre-operative clinical diagnosis was osteosarcoma. The abnormal calvarium was excised and histopathological examination confirmed the diagnosis of a predominantly intraosseous calvarial meningioma, WHO grade I.

Conclusions: The present case highlights the importance of histopathologic diagnosis in guiding therapeutic decisions and reiterates the necessity of considering PIM or meningiomas with extensive intraosseous component in the differential diagnosis of calvarial masses, even when imaging suggests a neoplasm with aggressive behavior, such as osteosarcoma.

Keywords: Case Reports; Meningioma; Osteosarcoma; Skull.

Figure 1. Schematic showing the location of the cranial mass in the patient’s parieto-occipital region.

Figure 2. Summary of case timeline.

Figure 3. A and B (coronal and sagittal views respectively) – Bone computed tomography (CT). Large midline permeative calvarial lesion with areas of thickening/erosion of the inner table and extensive periosteal reaction; C – Coronal post-gadolinium fat-saturated T1 sequence. Large intraosseous mass with demonstration of intracranial extension, invasion into the superior sagittal sinus, and regional dural thickening and enhancement.

Figure 4. Gross examination of the resected bone. The image shows a fragment of calvarium measuring 22.5 cm in its longest axis, 7 cm in the coronal plane, and up to 1.5 cm in thickness. The bone is expanded by a mass.

Figure 5. Photomicrographs of the tumor. A – Smear preparation showing cells with meningothelial differentiation forming whorls (H&E, 400x); B – predominantly intraosseous tumor with associated hyperostosis (H&E 200x); C – few scattered mitotic figures (red arrows) (H&E 400x); D – focally elevated Ki-67 proliferation rate (100x); and invasion into adipose tissue (arrow).