The majority of meningiomas arise from arachnoid cap cells, which are special cells of the arachnoid granules, while a few arise from fibroblasts of the dura mater or from arachnoid tissue attached to cranial nerves and choroid plexus. Chromosome 22 plays an important role in the development of meningioma, with a single chromosome seen in 72% of cases, and long-arm deletions are also more common. Neurofibromatosis type II is an inherited lesion that predisposes to meningiomas. Meningiomas may also be related to sex hormones, with tumors occurring in women, increasing in size during pregnancy, and progesterone, estrogen, or androgen receptors found in many meningiomas. Radiation therapy may also be a predisposing factor for meningiomas. Meningiomas often have an intact envelope and are mostly extracerebral tumors. There are two general morphologies, i.e., spherical, lobulated masses or flattened, with the latter being more likely to be found at the base of the skull. Tumors can infiltrate the dura mater and bone. Meningiomas often have a wide base at the dural attachment, while a few are narrow and have a stalked tumor. Usually, the tumor is clearly demarcated from the adjacent cerebral mass, with a lacunar subarachnoid space between them and an entrapped CSF and blood vessels. The blood supply of meningioma is abundant, mostly from the branches of meningeal artery, and there may be soft meningeal vessels involved in the blood supply in the peripheral parts of the tumor, and the blood supply of meningioma in the lateral ventricle comes from choroidal artery. The texture of the tumor can be soft or hard, depending on the amount of intra-tumor fibrous tissue and calcification. Foci of necrosis and hemorrhage are often seen within the tumor, but massive hemorrhage is rare, and sometimes cystic or yellow tumor-like changes can be found within the tumor. The peritumoral dura is often thickened in a circular reactive manner. Meningiomas can be classified into syncytial, fibrous, transitional, angiogenic, and interstitial types according to their cytologic manifestations, in addition to several subtypes. Currently, WHO classifies meningiomas into three types according to the active proliferation, aggressiveness and other biological behaviors: typical or benign meningioma, accounting for 88-94%; atypical meningioma, accounting for 5-7%; and mesenchymal type, i.e. malignant meningioma, accounting for only 1-2%. Site Meningioma is likely to occur near the venous sinus, cranial suture closure and arachnoid granules. Supratentorial meningiomas account for 90% of all meningiomas, and the common sites are the parsagittal sinus (25%) and the synovial surface (20%), the sum of which accounts for almost 1/2 of all meningiomas. The protruding surface originates in the dura mater of the cerebral surface and often occurs near the coronal suture. The third most common location on the episphere is the pterygoid crest (15-20%), of which 1/3 originate in the inner 1/3 of the pterygoid crest and often invade the optic canal. Meningiomas occurring in the saddle area and in the olfactory groove and the base of the prefrontal recess each account for 5-10% of meningiomas. Meningiomas in the posterior cranial recess account for about 10% of meningiomas, and the posterior border of the rocky bone, slope and cerebellar curtain are common sites. Approximately 2% of meningiomas are not attached to the dura mater and are usually located in the lateral ventricular triangle, starting from the choroid plexus mesenchymal cells or choroid plexus tissue. Other rare sites are the optic nerve sheath and the pineal region. Meningiomas that occur outside the dura of the central nervous system are rare, accounting for only 1% of cases, and can be found in the sinuses, nasal cavity, parotid gland, or scalp.