Meningeal osteochondroma simulating meningioma with metaplastic change: a rare golf-ball-like lesion of non-meningothelial mesenchymal origin.

Non-meningothelial mesenchymal tumors of the central nervous system (CNS), including those originating from the meninges, histologically correspond to tumors of soft tissue or bone. These individual entities arising from the meninges are rare, and probably have their origin in the multipotent primitive mesenchymal stem cells of the dura. Though it is a common bone tumor, the meningeal origin of osteochondroma has only very rarely been reported. We describe a case of a 35-year-old female with a well-demarcated, golf-ball-like osteochondroma of meningeal origin which was enucleated en bloc on craniotomy. Such a lesion can resemble a meningioma that exhibits metaplastic (osseous) change on imaging. However, provided that there is clinico-radiological awareness of such tumors, magnetic resonance imaging (MRI) can guide the way to this rare differential diagnosis, as it reflects the pathologic appearance of osteochondroma and allows the thickness of the cartilage cap to be estimated in order to check for rare malignant change. Complete excision along with the cartilage cap usually offers a favorable prognosis without recurrence.