The differential diagnosis of meningioma depends entirely on the suspected anatomic location of the tumor. No single symptom is diagnostic of a meningioma. Benign meningiomas grow slowly over years, and produce symptoms when they encroach on critical structures. These symptoms evolve gradually in contrast to the typical rapid symptom development in anaplastic astrocytoma, anaplastic oligodendroglioma, glioblastoma multiforme, metastases, primary central nervous system lymphoma, and medulloblastoma. In malignant meningiomas, which represent approximately 10% of meningiomas, symptoms may develop more rapidly.