Meningioma, also known as meningeal tumor, is typically a slow-growing tumor that forms from the meninges, the membranous layers surrounding the brain and spinal cord. Symptoms depend on the location and occur as a result of the tumor pressing on nearby tissue. Many cases never produce symptoms. Occasionally seizures, dementia, trouble talking, vision problems, one sided weakness, or loss of bladder control may occur.
Risk factors include exposure to ionizing radiation such as during radiation therapy, a family history of the condition, and neurofibromatosis type 2. They appear to be able to form from a number of different types of cells including arachnoid cells. Diagnosis is typically by medical imaging.
If there are no symptoms, periodic observation may be all that is required. Most cases that result in symptoms can be cured by surgery. Following complete removal fewer than 20% recur. If surgery is not possible or all the tumor cannot be removed, radiosurgery may be helpful. Chemotherapy has not been found to be useful. A small percentage grow rapidly and are associated with worse outcomes.
About one per thousand people in the United States are currently affected. Onset is usually in adults. In this group they represent about 30% of brain tumors. Women are affected about twice as often as men. Meningiomata were reported as early as 1614 by Felix Plater.
Signs and symptoms
Small tumors (e.g., < 2.0 cm) usually are incidental findings at autopsy without having caused symptoms. Larger tumors may cause symptoms, depending on the size and location. Focal seizures may be caused by meningiomata that overlie the cerebrum. Progressive spastic weakness in legs and incontinence may be caused by tumors that overlie the parasagittal frontoparietal region. Tumors of the Sylvian aqueduct may cause myriad motor, sensory, aphasic, and seizure symptoms, depending on the location. Increased intracranial pressure eventually occurs, but is less frequent than in gliomas. Diplopia (Double vision) or uneven pupil size may be symptoms if related pressure causes a third and/or sixth nerve palsy.
Causes
The causes of meningiomata are not well understood. Most cases are sporadic, appearing randomly, while some are familial. Persons who have undergone radiation, especially to the scalp, are more at risk for developing meningiomata, as are those who have had a brain injury. Atomic bomb survivors from Hiroshima had a higher than typical frequency of developing meningiomata, with the incidence increasing the closer that they were to the site of the explosion. Dental X-rays are correlated with an increased risk of meningioma, in particular for people who had frequent dental X-rays in the past, when the X-ray dose of a dental X-ray was higher than in the present.
Having excess body fat increases the risk.
A 2012 review found that mobile telephone use was unrelated to meningioma.
People with neurofibromatosis type 2 (NF-2) have a 50% chance of developing one or more meningiomata.
Ninety-two percent of meningiomata are benign. Eight percent are either atypical or malignant.
Genetics
The most frequent genetic mutations (~50%) involved in meningiomata are inactivation mutations in the neurofibromatosis 2 gene (merlin) on chromosome 22q.
TRAF7 mutations are present in about one-fourth of meningiomata. Mutations in the TRAF7, KLF4, AKT1, and SMO genes are commonly expressed in benign skull-base meningiomata. Mutations in NF2 are commonly expressed in meningiomata located in the cerebral and cerebellar hemispheres.
Pathophysiology
Meningiomata arise from arachnoidal cap cells, most of which are near the vicinity of the venous sinuses, and this is the site of greatest prevalence for meningioma formation. Some subtypes may arise from the pial cap cells that migrate during the development together with blood vessels into the brain parenchyma. They most frequently are attached to the dura over the superior parasagittal surface of frontal and parietal lobes, along the sphenoid ridge, in the olfactory grooves, the sylvian region, superior cerebellum along the falx cerebri, cerebellopontine angle, and the spinal cord. The tumor is usually gray, well-circumscribed, and takes on the form of the space it occupies. They usually are dome-shaped, with the base lying on the dura.
Locations
Parasagittal/falcine (25%) Convexity (surface of the brain) (19%) Sphenoid ridge (17%) Suprasellar (9%) Posterior fossa (8%) Olfactory groove (8%) Middle fossa/Meckel's cave (4%) Tentorial (3%) Peri-torcular (3%) Intraparenchymal (rare)