I. What is meningioma
Meningiomas are tumors that occur in the meningeal tissue on the surface of the brain and originate 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.
Causes and prevalence of meningioma
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 was not widely available, meningiomas were often detected only when they grew very large. 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 young 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 prescribing an MRI based on the patient’s clinical symptoms such as epilepsy, weakness, sensory loss, and cranial nerve dysfunction, which is then combined with the patient’s MRI findings.
Although most meningiomas are benign lesions, they can also have malignant progression. The World Health Organization classifies meningiomas according to the histological characteristics of the tumor as follows.
1. benign (grade I): 90% of them are endothelial, fibrous, migratory, gravel body and hemangioma types (the most aggressive)
2, atypical (grade II): 7%, with choroidal type, clear cell type and atypical.
3.Interstitial/malignant (grade III): 2%, with papillary type, transverse myeloid type and interstitial type.
IV. Clinical manifestations of meningioma
Small tumors (less than 50px in diameter) mostly do not cause clinical symptoms and are often discovered by chance. The clinical symptoms caused by large tumors are determined by the size and growth site of the tumor.
1. focal seizures may be caused by meningiomas on the cerebral hemispheres.
2. progressive limb weakness may be due to a meningioma in the parsagittal sinus of the frontoparietal lobe
3. peri-lateral fissure meningiomas, in turn, may cause motor, sensory, aphasia and seizure symptoms, depending on the site of the tumor
4. causing increased intracranial pressure.
V. Treatment of meningioma
1.Observation
Generally speaking, if the diagnosis is correct, the meningioma is less than 3 cm in diameter, and there is no meningioma causing the corresponding symptoms, it can be dynamically observed and temporarily not operated. In the beginning, MRI is often repeated 2-3 months after the last examination, and if there is no change, observation is continued. Subsequently, the review is repeated six months after the last MRI, and if there is still no significant increase in meningioma, the review interval can be set at one year.
Special sites such as saddle node meningioma and pontocerebellar horn meningioma may have symptoms such as vision loss visual field defects when the tumor is relatively small, and the tumor may be 1-2 CM in diameter or even a few millimeters, which also requires surgery.
During the observation period, if signs of tumor progression such as significantly enlarged meningioma or expanded peritumor edema and corresponding symptoms are found, surgery should be arranged as soon as possible. Observation is not recommended for patients with tumors that have already caused clinical symptoms. Close imaging review needs to be combined with a measure to rule out tumor enlargement.
2.Surgical resection
The “idealized treatment” of meningioma is evolving with the advent of new technologies. There are often multiple correct treatments for the same tumor, and opinions on how best to treat a particular tumor often vary among neurosurgeons. Craniotomy has long been recognized as the standard of care for large or clinically symptomatic meningiomas. Innovations in microsurgical techniques and the use of computer-assisted positioning techniques during surgery have greatly increased the ability of neurosurgeons to successfully remove tumors.
For meningiomas that are superficial and easily accessible, located on the dural surface, surgical excision can result in permanent cure. If the skull bone adjacent to the tumor is eroded, total removal of the lesion is more difficult.
3.Radiotherapy
Radiotherapy includes photon beam and proton beam therapy or fractionated external radiation therapy. The majority of medical centers use modified linear accelerator systems or gamma knives to treat patients. Radiation therapy can be used as an alternative to surgery for small tumors that are far from vital structures. Fractionated external radiation therapy can also be used as the treatment of choice for tumors that are difficult to remove surgically or for patients who cannot be operated on for medical reasons. The potential risks of radiotherapy are cerebral edema and neurological deficits.
For patients with sub-total resected WHO grade I meningiomas, postoperative radiotherapy is often required. The clinical decision to follow subtotal resection with adjuvant radiotherapy is somewhat controversial, as no cases of tumor control in patients with WHO grade I meningiomas exist on this issue. Numerous retrospective studies have strongly demonstrated that adjuvant radiotherapy after subtotal resection prolongs tumor progression-free survival and overall survival. Radiotherapy is an effective treatment option for small tumors involving the skull base (including those in the cavernous sinus) and for meningiomas closely associated with the venous sinus.
For patients with WHO grade II and III meningiomas, the current standard of care is postoperative adjuvant radiotherapy, regardless of the extent of surgical resection. This is because of the relatively high rate of postoperative local recurrence of these high-grade tumors.
4. Traditional chemotherapy
Current chemotherapy is basically ineffective. Anti-progestational drugs have been used, but with varying results. Recent studies have found that hydroxyurea drugs can reduce the size of unresectable tumors and recurrent meningiomas, but these need to be further evaluated.
Prognosis of meningiomas
Meningiomas are generally benign, slow-growing tumors, and the prognosis for patients is generally good. For patients with meningiomas requiring treatment, both surgical resection and radiation therapy are acceptable treatment modalities. In the past, microsurgical total resection of tumors was often the favored approach of the vast majority of neurosurgeons. This remains true for convex meningiomas that are easily accessible and completely resected with a low recurrence rate. However, with the widespread use of radiotherapy worldwide, surgeons need to rethink the aggressive surgical procedures performed on complex meningiomas. Radiotherapy has now been shown to provide patients with long-term tumor control and a low rate of tumor recurrence. The choice of meningioma treatment is determined on a patient-by-patient basis by an experienced neurosurgeon.
The likelihood of recurrence or continued growth of meningioma after surgery can be assessed using the WHO classification of the tumor and the Simpson classification of the extent of surgical resection.