Meningiomas account for over 30% of central nervous system tumors in adults, making them the most common tumors in this category. Within the central nervous system, most meningiomas arise on the intracranial or spinal dural surface and rarely from an intraventricular position. They originate from a protective layer around the central nervous system, called meninges, and specifically from cells in the outer layer of the arachnoid mater. The incidence of meningioma increases with age. They are often diagnosed by chance. A widely mentioned risk factor is ionizing radiation. Other associated risk factors such as head injury, smoking, and cell phone use have not been proved. Another established risk factor is neurofibromatosis type 2.
Types
There are 3 types of meningiomas:
Benign meningioma: It is the most common type of meningioma. Benign meningiomas do not invade the surrounding brain tissue. It is also called grade I meningioma.
Malignant meningioma: Also called grade III meningiomas, these tumors make up only 1% of all meningiomas. They can either happen in this malignant form or progress from benign meningioma. This type of meningioma can invade surrounding brain tissue and, in rare cases, spread to other organs such as the lungs.
Atypical meningioma: It is recently recognized as the 3rd type of meningioma by the WHO. Histological and clinical features of this type are in between those of benign and malignant meningioma.
Global perspective
The overall incidence of meningiomas is 8.3 per 100,000 persons-year. Benign meningioma is often diagnosed during the mid-years of life. Around 300 malignant meningiomas are diagnosed in the US every year. Malignant meningioma is mostly diagnosed between the ages of 75 and 84 years. Their overall survival is 2–3 years. Benign meningiomas are more common in females with a male to female ratio of 1:2. Whereas malignant meningiomas are equally prevalent in males and females.
Indian perspective
Similar to the rest of the world, meningioma is the most common primary brain tumor in India. It is being effectively treated in India with a success rate of 95%. Patients can choose from a variety of available hospitals.
Signs and symptoms
Most meningiomas are benign but when they are aggressive, they cause focal neurological deficits such as seizures that greatly affect the quality of life. The specific signs and symptoms of a meningioma depend upon its location in the central nervous system. Meningiomas usually do not spread to other parts of the body hence, the symptoms are mostly focal.
In many patients, the growing tumor causes increased intracranial pressure which manifests itself as a headache.
Other common symptoms arise due to the compression of the tumor against a cranial nerve. In this case, the symptoms are highly related to the functions of that particular cranial nerve.
Meningiomas growing near the anterior portion of the brain cause personality changes, confusion, and an altered level of consciousness.
Diagnosis
Upon the evaluation of symptoms, neuroimaging provides the incidental diagnosis of a meningioma. Magnetic resonance imaging (MRI) is a widely used imaging modality for the initial diagnosis and surveillance of meningioma. Imaging alone cannot differentiate between benign and malignant meningiomas. A meningioma associated with edema has more chances of being a malignant one. Another clue is the rate of growth of the tumor. Since active surveillance is the first line of care provided in meningiomas, the rapid growth of the tumor can alarm pathologists about the possibility of malignant meningioma. Histological confirmatory diagnosis is the ultimate way of differentiating between these two types. For histologic examination, tumor tissue obtained by biopsy is stained and observed in higher magnification. Meningiomas have characteristic spiral formations called whorls. The immunohistochemical examination provides another layer of specificity. In this method, a marker of meningiomas, called epithelial membrane antigen, is identified using immunostaining.
Management
Similar to other primary brain tumors, the treatment options for meningiomas consist of surgery, radiotherapy, and chemotherapy.
Surgery: Surgical resection is the mainstay of meningioma treatment. Gross surgical resection can result in a very low incidence of recurrent meningiomas. However, gross total resection comes with the inherent risk of damaging the surrounding structures damaging nearby areas of the brain and the resulting morbidity greatly reduces the quality of life of the patients. Common morbidities resulting from surgery are decreased level of consciousness, cranial nerve neuropathies, hemiparesis, and dysphasia. To counter this problem, near-total resection is preferred and the remaining tumor is eliminated via radiotherapy and adjuvant chemotherapy. This approach is made easier due to the emergence of innovative radiation therapy techniques such as stereotactic radiotherapy. Most malignant meningiomas recur after about 2-3 years of the initial surgery and may require another resection.
Radiotherapy: External beam therapy (EBRT) is the preferred type of radiotherapy and it is given as a total dose of 60 Gy after resection. This results in an increase in progression-free survival of 5 years in up to 80% of the patients. As mentioned above, stereotactic radiotherapy has helped limit the morbidities associated with a gross total surgical resection. Brachytherapy is another innovative way of delivering radiation to the tumor internally that can have additional advantages over traditional methods.
Chemotherapy: In grade, I meningioma patients, several chemotherapeutic agents are effective as adjuvant treatment. These are temozolomide, irinotecan, interferon-α, somatostatin analogs pasireotide or sandostatin, and RTK inhibitors. Chemotherapy is ineffective in malignant meningiomas. Among the chemotherapeutic agents which have been tried are dacarbazine and adriamycin, hydroxyurea, temozolomide, and irinotecan. Targeted therapy with hormonal drugs has not been reported to have produced any encouraging results as well.
Quality of life
Meningiomas are frequently benign but sometimes they cause symptoms such as seizures, headache, blurred vision, and confusion that severely impair the quality of life of the patients. Treatment of symptomatic meningiomas is associated with improved health-related quality of life (HRQoL), cognitive functioning, and seizure control. Although tumor resection increased HRQoL, long-term follow-up showed persistent reduced HRQoL compared with healthy controls. This is due to damage to vital parts of the brain during surgical resection. Speech or occupational therapy and physiotherapy can improve some of the morbidities of neurosurgery. Other measures such as reducing stress, eating a nutrient-rich diet, daily exercise, and adequate sleep are also beneficial as supportive therapies which may act as adjuvants to improve the quality of life of the patients.
