Meningioma is a tumor that occurs in the meningeal tissue on the surface of the brain and originates from the arachnoid granule cells. Most meningiomas are benign, however, a few are malignant. Meningiomas account for approximately one-fifth of all intracranial primary tumors and rank as the second most common primary tumor of the central nervous system. As a benign tumor, it tends to grow slowly, often over many years. It is because of this slow growth that tumors are sometimes detected only after they have grown so large. About a quarter of meningioma patients have epilepsy as the initial clinical manifestation, while the rest have the dominant effect (headache, vomiting, etc.) caused by tumor growth as the main symptom. Most cases of meningioma are disseminated, but some cases are familial. Patients who have received radiation to the scalp are significantly more likely to develop meningiomas. The most common genetic mutation in meningioma patients is an inactivating mutation in the neurofibromatosis type 2 gene on the long arm of chromosome 22. Meningiomas tend to occur in the arachnoid cells near the venous sinuses, so these are also good sites for meningiomas. They are often attached to the dura mater in these areas. Preferred sites for meningiomas are the parsagittal sinus in the superior frontoparietal lobe, the pterygoid crest, the olfactory groove, the lateral fissure, the falx cerebri, and the pontocerebellar horn. The tumor is usually round with rich blood supply and the base is located on the dura mater. Diagnosis of meningioma In the past, when advanced imaging equipment (CT, MRI, etc.) was not popular, meningioma often grew very large before being detected. At that time, meningiomas could only be diagnosed when severe clinical symptoms appeared or when they penetrated the skull to form a visible protrusion. Now, with the advent of extensive CT and MRI, meningiomas can be diagnosed at a relatively early age. Meningiomas are easily detected on enhanced CT scans and MRI, which is currently the most valuable diagnostic tool for screening and confirming meningiomas, and CT’s “bone window” and “3-D reconstruction techniques” can be useful in some cases. In some cases, cerebral angiography can be useful to determine the arterial supply and venous return to the tumor. The diagnosis of meningioma is usually made by a physician who prescribes an MRI based on the patient’s clinical symptoms such as epilepsy, weakness, sensory loss, cranial nerve dysfunction, etc. This is then combined with the patient’s MRI findings. Many meningioma patients are now diagnosed as an “accidental finding” – when the patient undergoes imaging for unrelated symptoms. It is not uncommon for patients to be diagnosed with a meningioma as a result of a CT scan following a car accident or other traumatic brain injury. Although most meningiomas are benign lesions, they can also progress malignantly. The World Health Organization (WHO) classifies meningiomas according to their histologic characteristics as follows: 1. benign (grade I): 90%, endothelial, fibrous, migratory, gravelly body, and hemangioma (the most aggressive); 2. atypical (grade II): 7%, choroidal, clear cell, and atypical; 3. mesenchymal/malignant (grade III): 2%, papillary, transverse muscle type and interstitial type. Clinical manifestations of meningioma Small tumors (less than 2.0 cm in diameter) mostly do not cause clinical symptoms and are often discovered by chance. Clinical symptoms caused by large tumors depend on the size and location of the tumor: 1. focal seizures may be caused by meningiomas on the cerebral hemispheres; 2. progressive limb weakness may be caused by meningiomas in the parsagittal sinus of the frontoparietal lobe; 3. meningiomas around the lateral fissure may cause motor, sensory, aphasia, and epilepsy symptoms, depending on the location of the tumor; 4. increase in intracranial pressure.