Meningiomas are the most common primary central nervous system tumor. These extraaxial tumors can arise from the dura at any site along the neuroaxis, although are most frequently found at the skull base or in the parasagittal region. On magnetic resonance imaging (MRI), they typically appear iso- to slightly hypointense on T1-weighted sequences and hyperintense on T2-weighted sequences. Most characteristic is robust homogenous enhancement on postcontrast imaging; without contrast, small meningiomas may be easily missed. Calcifications may be present, and are best appreciated on computed tomography. A “dural tail,” or an adjacent tapering dural thickening, can often be seen. Although these radiographic findings are quite specific for meningioma, very rarely lymphoma, sarcoidosis, and tuberculosis may produce similar-appearing radiographic lesions.
While most meningiomas are sporadic, identified risk factors for meningioma development include NF2 gene deletion and ionizing radiation exposure. NF2 is the tumor suppressor gene mutated in neurofibromatosis type 2, which can result in multiple meningiomas, schwannomas, and gliomas and has an autosomal dominant inheritance. Meningiomas are also associated with other tumor suppressor gene mutations, including NF1 , VHL , and PTEN (which are present in neurofibromatosis type 1, Von Hippel-Lindau, and Cowden syndromes, respectively).
Meningiomas are often benign incidental findings on neuroimaging; however, progressive tumor growth can result in focal neurologic deficits from displacement or compression of adjacent cerebral and vascular structures. If causing significant mass effect with resulting neurologic symptoms, dexamethasone should be given. Meningiomas may also serve as a seizure focus, with seizure the presenting symptom in 20%–50% of patients. When seizures occur, antiepileptic medication is indicated. However, prophylactic antiepileptic use is not recommended.
In cases of persistent symptoms, refractory seizures and/or neuroimaging suggestive of high-grade features, surgical resection is the standard therapeutic option. However, radiation therapy alone can be considered if the mass is not amenable to surgery. If the patient is asymptomatic or has controlled epilepsy, serial MRI can be performed every 6–12 months for 2–3 years to assess for meningioma growth, followed by clinical monitoring if there is radiographic stability.
The World Health Organization (WHO) Classification of Central Nervous System Tumors, based on histopathologic features, is used for meningioma grading. About 90% of meningiomas are WHO grade I and histologically benign. If complete resection, including the dural attachment and potentially infiltrated bone, is achieved, the rate of recurrence is low (3%–10% at 5 years). However, this rate increases to 10%–50% with incomplete resection. Therefore, focal radiation should be considered for cases of subtotal resection. For incompletely resected grade I meningiomas, radiographic follow-up for tumor growth should be obtained approximately every 6–12 months. For completely resected grade I meningiomas, radiographic follow-up for tumor recurrence may be performed less frequently, such as annually for 5 years, then every 2 years.
WHO grade II meningiomas have atypical histologic features, characterized by mitotic activity or at least three of the following features: increased cellularity, small cells with a high nucleus to cytoplasm ratio, large and prominent nucleoli, abnormal growth pattern, and necrosis. Grade II meningiomas have a higher rate of recurrence (30%–40% at 5 years). While adjuvant radiation is standard in cases of subtotal resection, it may also be considered after complete resection; however, this remains controversial. Given the higher rate of tumor recurrence, radiographic surveillance following treatment should be performed more frequently than with grade I meningiomas, such as every 6 months for 5 years, then annually.
Only 1%–3% of meningiomas are WHO grade III. These are histologically anaplastic, featuring an increased number of mitotic figures (20 or more per 10 high-power field) or frank sarcomatous or carcinomatous features, and are clinically aggressive with recurrence rates of 50%–80% at 5 years. Adjuvant radiation therapy is recommended, regardless of the extent of resection. Radiographic surveillance following treatment should be obtained every 3–6 months.
In the case of tumor recurrence, repeat surgery and/or radiation therapy can be considered. There is otherwise limited evidence for systemic chemotherapy, immunotherapy, or hormonal therapy use in recurrent meningiomas. However, targeted therapy research is ongoing, and thus clinical trials should be considered.