Page last modified: August 22, 2020
|Sagittal view of an incidental meningioma||Coronal view of an incidental meningioma affecting the temporal lobe (same as left)||Falx meningioma, again incidental.|
Meningiomas are slowly growing tumors that arise from the coverings of the brain (the meninges). Most of them are "incidental", meaning that they are found during the course of an investigation for some other process. Incidental meningiomas are usually checked occasionally to see if they have enlarged, but otherwise are ignored. Meningiomas are not quite as common as pituitary adenoma's. Fortunately, the most common two brain tumors -- meningiomas and pituitary adenomas, are not malignant, and are rarely threats to life.
Meningiomas are much more common over the age of 65 (Cohen-Inbar, 2019). They tend to grow more slowly in older people.
Rarely, meningiomas have malignant transformations. This is infrequent (Wang et al, 2015). Meningiomas may be more common in persons who have had radiation treatments to the skull, or many diagnostic procedures involving X-rays to the skull. (Choudhary et al, 2006; Partington and Davis, 1990) There have also been reports post gamma-knife (i.e. gamma-rays). (Sheehan et al, 2006)
Most meningiomas are asymptomatic. Dizziness is an occasional symptom, mainly when they occur in the "posterior fossa", which is the lower part of the brain including the cerebellum and brainstem.
Dizziness associated with meningiomas mainly occurs when it impinges on the 8th nerve or the cerebellum. Because these tumors grow very slowly, people with them gradually accommodate to them over years, and often their effects are unnoticed.
When meningiomas are in the same location where acoustic neuromas are commonly found (IAC), they may be mistaken for them. In this situation, surgery may need to be modified. Ordinarily meningiomas do not do as much damage to the 8th nerve as acoustic neuromas as they are tumors of the covering of the nerve rather than of the nerve itself. For this reason, after an IAC meningioma is removed, there may still be considerable vestibular function.
Usually a meningioma is found as an incidental finding on a scan of the brain. They "light up" with contrast on CT scan images, and they are also easily seen on MRI images. If contrast is not used, these may be missed.
An extension of this idea, is that CT scans (such as are routinely done in emergency rooms after concussions or for a headache), when done without contrast, can miss brain tumors like a meningioma, because meningiomas are best seen with contrast, and may have very little swelling. The two images above show a meningioma on MRI on the left, and a similar view on the CT scan done on the right (without contrast). The meningioma was missed.
So in other words, if there is no contrast, a CT scan may miss a brain tumor.
Meningiomas in "sensitive places", are more likely to be operated or radiated. The image above shows a very successful result of radiation. The scan on the left was done 10 years prior to the scan on the right. A few months after the scan on the left was done, fractionated sterotaxic radiation was used to treat the tumor. As can be seen, it has largely vanished, without any adverse effects
Watchful waiting is the main management of meningiomas. If the tumors grow large enough to impair function, then they are removed surgically or radiated. Cohen-Inbar (2019) discussed the risks of management, comparing watchful-waiting to surgery or radiation. Growing or symptomatic meningioma's are usually selected for the more aggressive approach.
Seizures are common in meningiomas that are in the upper part of the brain (supratentorial), after surgical resection. (Englot et al, 2016). Of course surgery also has the risk of infection and anesthesia. The advantages of surgery over radiation is there can be less "collateral damage" due to the radiation, and less of a chance of delayed radionecrosis.