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 The latter include atypical, clear cell, chordoid, rhabdoid, papillary meningiomas (WHO grade 2) and mesenchymal/malignant meningiomas (WHO grade 3). The majority of meningiomas are benign, and only about 10% are non-benign.
Clinical manifestations
Most meningiomas are 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 have malignant growth, develop faster and have a shorter course.
2. Symptoms of increased intracranial pressure appear late, especially in elderly patients. Because the tumor grows slowly, 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 focal neurological irritation symptoms first. Seizures and other stimulation symptoms often appear before neurological paralysis symptoms (such as hemiparesis, aphasia, visual field loss, etc.), which is determined by the slow and swelling growth of meningioma.
4. Cranial involvement. Meningioma can cause proliferation or destruction of adjacent cranial bones. It can cause hyperplasia and thickening of the inner plate of the skull, and in a few cases, it can cause local thinning and destruction of the bone plate. In some cases, the tumor can grow to the lower part of the scalp and form a mass.
Auxiliary examination
MRI: It is the most important diagnostic method at present. MRI scan and enhancement scan can show the relationship between tumor and surrounding brain tissues and neurovascular, 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 more clearly show the osteophytes or destruction of tumor base, and also better show the calcification and bleeding of tumor.
3.MRV: It can clearly show the invasion of the venous sinus by the tumor and understand whether the venous sinus is narrowed or occluded by the tumor compression.
4.DSA: As an invasive examination method, not every meningioma patient needs DSA examination, but it can show the information of vascular displacement caused by meningioma, the relationship between tumor and venous sinus, tumor blood supply artery and drainage vein, which is helpful to design surgical plan. Preoperative embolization can provide help to reduce intraoperative bleeding in cases with abnormally rich 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 shows a substantial lesion with significant enhancement, but meningioma has a longer history and slower development, and cystic necrosis is rare on imaging, often with meningeal tail signs.
2. Hemangiopericytoma: It has many similarities with meningioma, and the WHO classification after 1993 separated it from meningioma. However, hemangioepithelioma is prone to recurrence and intracranial and extracranial metastasis. The tumor is particularly rich in blood supply and usually has no calcification and osteophytes, and some cases have local bone destruction.
3.Hemangioblastoma: The tumor is rich in blood supply, with obvious enhancement and often visible vascular flow hollow shadow.
4.Nerve sheath tumor: tumor often has cystic change, no meningeal tail sign, generally no calcification, etc. can help to differentiate.
5.Metastasis: it has the characteristics of rapid development, often with primary lesions, common tumor necrosis cystic lesions, and often obvious edema around the tumor.
Treatment
1.Surgery: It is usually the first choice of treatment. For those who have the condition, the tumor, its attached dura mater and the invaded skull should be completely removed to reduce recurrence.
2.Stereotactic radiosurgery includes Gamma knife, X-knife, radio-wave knife, etc. It is suitable for patients with more difficult surgical resection and higher risk. It is suitable for tumors in more difficult and risky areas (such as cavernous sinus), or those who cannot be fully resected by surgery, or those whose physical condition cannot tolerate craniotomy, and the tumor diameter should be <3cm. 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 is higher after radiation neurosurgery treatment.
3.General radiotherapy: It is mainly used as adjuvant treatment after surgery for non-benign meningioma (such as atypical meningioma and mesenchymal meningioma) to delay recurrence.
4.Interventional therapy is mainly used as adjuvant treatment before surgery to reduce tumor blood supply through preoperative embolization to facilitate surgical resection, mainly for tumors with abnormal rich blood supply where external carotid artery is the main blood supply.
5.Other therapies There are no successful reports about drug treatment for meningioma. The efficacy of hormone receptor antagonists, interstitial radiotherapy, etc. is uncertain and needs further study.
Management of recurrent meningioma
For the treatment of recurrent meningioma, depending on the growth site of the tumor, tumor size, patient’s age, and physical condition, surgery should be preferred if it is less likely to cause serious disability or risk. For those who are not suitable for re-operation, measures such as Gamma knife, X-knife or general radiation therapy can be used as appropriate.
Management of asymptomatic meningioma
With the popular use of CT and MRI, a number of patients are clinically asymptomatic when meningioma is detected. For asymptomatic meningiomas that show calcification on imaging, have a hard texture (low or iso-signal on MRIT2), 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%.