Intracranial meningioma is the second most common brain tumor in humans, accounting for approximately 20% of intracranial tumors, after glioma. Approximately 90% of meningiomas are benign tumors, with a male-to-female ratio of approximately 1:2, but malignant meningiomas are more common in men. Meningiomas originate from intracranial arachnoid cells and are most common in the convex surface of the brain, parsagittal sinus, pars falciformis, and skull base (e.g., pterygoid crest, olfactory groove, pontocerebellar horn, etc.). Etiology The etiology of meningiomas is not fully understood. Meningiomas originate from arachnoid cells, but the division rate of arachnoid cells is very low, so external factors must be involved in the development of meningiomas. It is generally believed that the occurrence of meningioma may be the result of a combination of endogenous factors (e.g., chromosome 22 gene abnormalities, estrogen, growth factors and receptors) and exogenous factors (e.g., trauma, radiation damage, viral infection, etc.). Pathology In 2000, the World Health Organization classified meningiomas into two categories: meningiomas with low risk of recurrence and non-invasive growth (WHO grade 1, benign) and meningiomas with high risk of recurrence and/or invasive growth (WHO grade 2 or 3, non-benign), the former including endothelial, fibrous, sarcoid, angiomatous, microcystic, secretory, lymphoplasmacyte-rich, and saprophytic types, and the latter including atypical, clear cell, chordoid, rhabdoid, papillary meningiomas (WHO grade 2) and mesenchymal/malignant meningiomas (WHO grade 3). The majority of meningiomas are benign tumors, and only about 10% are non-benign. Clinical manifestations 1. Meningiomas are mostly benign, with slow growth and long course. There are reports of meningioma with early symptoms for an average of 2.5 years and a few for as long as 6 years. However, a few meningiomas grow malignantly, develop faster and have a shorter course; 2. The symptoms of increased intracranial pressure appear later, especially in elderly patients. Because of the slow growth of the tumor, the neural tissue has sufficient time to adapt to the growth of the tumor, so often the tumor grows very large while the symptoms remain mild. Patients may have severe optic papilloedema or already have significant secondary optic nerve atrophy, but no significant headache, vomiting, or other symptoms of cranial hypertension. In elderly patients, the symptoms of cranial hypertension appear later because there is often senile brain atrophy and more intracranial compensatory space. However, when the tumor grows very large and the nervous system loses compensation, the condition can deteriorate rapidly and even brain herniation can occur; 3. Generally, there are mostly focal neurological irritation symptoms first. Seizures and other irritation symptoms often appear before neuroparalysis symptoms (such as hemiparesis, aphasia, visual field loss, etc.), which is determined by the slow and expansive growth of meningiomas; 4. Meningioma can cause proliferation or destruction of adjacent cranial bones. It can cause hyperplasia and thickening of the inner plate of the skull, and a few can cause local thinning and destruction of the bone plate. In some cases, the tumor can grow below the scalp and form a mass. MRI is the main diagnostic method at present. MRI scan and enhancement scan can generally show the relationship between tumor and surrounding brain tissues and neurovascular more clearly, which can help to judge the tumor texture and blood supply, show peritumor edema, tumor shape and size, meningeal tail sign and other information; 2.CT Compared with MRI, CT can show the bone growth or destruction of tumor base more clearly. 3.MRV can clearly show the invasion of venous sinus by tumor, and understand whether the venous sinus is narrowed or occluded by tumor compression; 4.DSA as an invasive examination method, not every meningioma patient needs DSA examination, but it can show the displacement of blood vessels caused by meningioma, the relationship between tumor and venous sinus, tumor blood supply artery and drainage vein. However, it can reveal information about the vascular displacement caused by meningioma, the relationship between the tumor and the venous sinus, the tumor-supplying artery and the draining vein, which is useful for designing surgical plans. Preoperative embolization can be helpful in reducing intraoperative bleeding in cases with abnormal blood supply. For determining the involvement of venous sinus, it has been replaced by MRV. Differential diagnosis 1. Glioblastoma Glioblastoma growing close to the convex surface of the brain or skull base often presents as a significantly enhancing substantial lesion, but meningioma has a longer history, develops more slowly, and cystic necrosis is rare on imaging, often with meningeal tail signs; 2. Hemangiopericytoma There are many similarities with meningioma, and the WHO classification after 1993 separates it from meningioma. However, hemangioepithelioma is prone to recurrence and intracranial and extracranial metastasis. The tumor is particularly rich in blood supply, and there is usually no calcification and osteophytes, and some cases have local bone destruction; 3. The tumor often has cystic lesions, no meningeal tail sign, and generally no calcification can help to differentiate; 5. Treatment 1.Surgery is usually the first choice of treatment. For those who have the conditions, the tumor, its attached dura and the invaded skull should be completely removed to reduce recurrence. 2.Stereotactic radiosurgery includes Gamma knife, X-knife and radio-wave knife. It is suitable for tumors in difficult and risky areas (such as cavernous sinus), or tumors that cannot be fully resected by surgery, or those who cannot tolerate craniotomy in physical condition. If the tumor is located in the parsagittal, pars falciform, lateral fissure, or near the main reflux vein of the cortex, the risk of cerebral edema after radiation neurosurgery is higher; 3.General radiation therapy is mainly used as adjuvant therapy after surgery for non-benign meningioma (such as atypical meningioma and mesenchymal meningioma) to delay recurrence; 4.Interventional therapy is mainly used as adjuvant therapy before surgery to reduce the blood supply of the tumor through preoperative embolization to facilitate It is mainly used for tumors with abnormally rich blood supply mainly in the external carotid artery supply; 5.Other therapies There are no successful reports on drug therapy for meningioma. The efficacy of hormone receptor antagonists, interstitial radiotherapy, etc. is uncertain and needs further study. Treatment of recurrent meningioma For the treatment of recurrent meningioma, according to the tumor growth site, tumor size, patient’s age, physical condition and other factors, surgery should be preferred if it is less likely to cause serious disability or danger by re-operation. For those who are not suitable for re-operation, measures such as Gamma knife, X-blade or general radiation therapy can be used as appropriate. Management of asymptomatic meningioma With the popular application of CT and MRI, many patients are clinically asymptomatic when meningioma is found. For asymptomatic meningiomas that show calcification on imaging, have a hard texture (low or iso-signal on MRI T2), and are small in size (<3 cm in diameter), surgery can potentially be avoided, but close follow-up observation is required. Meningiomas should be followed up once every 3 months after discovery, and then annually or every other year thereafter if there is no significant growth. Surgery is required when tumors are found to be rapidly increasing in size or when symptoms develop. Prognosis The 5-year overall survival rate for meningiomas is 69% and decreases with age. 81% of patients aged 21-64 years and 56% of those aged ≥65 years have a 5-year survival rate. Patients' operative mortality and prognosis are related to age, physical condition, tumor location, tumor nature, and whether total resection is performed. In general, meningioma patients with advanced age, poor physical condition, deep tumor location, mesenchymal and atypical meningiomas, and failure of complete tumor resection have relatively poor prognosis. The 5-year recurrence rate of benign meningioma with total surgical resection is 20.5%. The 5-year recurrence rate of malignant meningioma has been reported to be 78%.