Three layers of membranes—meninges—cover the brain and spinal cord: the dura mater, the arachnoid and the pia mater. And when a tumor of one or more of these layers occurs, the result is known as meningioma, or a primary (developing and remaining in one place) intracranial tumor.

Usually benign and very slow growing, meningiomas, if not detected and treated, can become a problem as they have the ability to interfere with the normal functioning of the brain. Indeed, if they grow to a large enough size they can cause significant disabilities and even be fatal. And whereas an individual typically only develops a single meningioma, it is possible for several of the tumors to occur at once throughout the brain and spinal cord.

Meningiomas are categorized into one of three grades: a benign meningioma grows the slowest and has a very low rate of recurrence; an atypical meningioma is slightly more aggressive in that it can develop more rapidly and may occur more than once; and a malignant or anaplastic meningioma is very aggressive and will likely recur again and again.

Although the exact cause of meningiomas is unknown, in simplest terms tumors are abnormal growths due to unnecessary cell multiplication that serves no proper function in the human body. Typically, cell multiplication is controlled by suppressor genes, which continually act to protect cells from cancer-causing genes known as oncogenes. However, when suppressor genes fail because of changes in their protein coding, tumor can develop as cell division becomes unregulated.

Whereas our body’s built-in defenses find and destroy these abnormal cells, naturally occurring chemicals sometimes hamper the ability of our immune system to see these cells, as which point they become strong enough and exist in large enough numbers to overpower any of body’s defenses.

Because it is benign, only when a meningiomas has grown quite large do symptoms become noticeable. And in fact some meningiomas never show signs of their existence at all. However, when symptoms do appear they will vary depending on the tumor’s size and location, and may include headaches, seizures, changes in mood and behavior, generalized confusion, nausea and vomiting and vision problems.

Again, because they don’t typically present with symptoms, meningiomas are often discovered during a routine brain scan for another condition or during a neurological examination when a physician tests the functions of the eyes, ears, nose and muscles as well as a patient’s balance and coordination, mental acuity and memory. In the event that a meningioma is suspected, imaging tests will ordered (CT scans and MRIs) which can determine the size, type and exact location of the tumor. Additionally, a biopsy can confirm the tumor’s nature.

If symptoms are non-existent or mild and there’s no impact to the patient’s quality of life, it’s likely that simple observation will be ordered. However if treatment is necessary surgery is usually recommended to remove the tumor and all affected cells and is proven to be very effective. If the whole tumor cannot be removed safely or if a return of the tumor is likely, radiation therapy may be necessary as well.