Meningioma Health Article

Definition

A meningioma is a benign tumor of the central nervous system that develops from cells of the meninges, the membranes that cover and protect the brain and spinal cord.

Description

The meninges

The delicate tissues of the brain and spinal cord are protected by a layer of bone and an inner covering called the meninges. The meninges are composed of three layers:

• dura mater
• arachnoid
• pia mater

The tough, thick dura mater forms the outer layer of the meninges and is attached to the bone of the skull and spinal cord. The arachnoid and pia mater layers are thinner and more delicate than the dura mater. The innermost pia mater layer is attached directly to the brain and spinal cord. Meningiomas arise from the middle arachnoid layer, and most remain attached to the dura mater by a dural tail.

Types of meningiomas

Meningiomas account for 15-20% of all brain tumors, and 25% of all spinal cord tumors. The World Health Organization (WHO) classifies meningiomas into 11 different categories according to their cell type. However, because there are so many different cell types and so much overlap between types, meningiomas are most often placed into three general categories, including benign, atypical, and malignant.

Benign meningiomas are by far the most common, accounting for more than 90% of all meningiomas. These tumors grow slowly and produce symptoms only if they become large enough to compress nearby brain tissue. In some patients, meningiomas can grow very large with almost no symptoms. This happens because the tumor has grown very slowly and has gradually compressed the brain over time. Meningiomas can also cause fluid to build up in the brain, and can sometimes block veins. They may also grow into nearby bone, causing the bone to become thicker.

Up to 7% of meningiomas are classified as atypical. These tumors grow more quickly than benign meningiomas and are more likely to be symptomatic. Malignant meningiomas are fast-growing aggressive tumors and are the most rare, accounting for only about 2% of all meningiomas. It is extremely unusual for meningiomas to metastasize to other organs. When they do, the lungs are the most common site.

Only about one tenth of meningiomas are found in the spine. These slow-growing tumors cause symptoms when they begin to compress the spinal cord. Spinal meningiomas usually grow in the spinal canal between the neck and the abdomen, and are almost always benign.

Demographics

Only one person in every 50, 000 is diagnosed with a symptomatic meningioma annually. Most of these patients are women. Women develop brain meningiomas almost twice as often as men and spinal meningiomas four to five times more often than men. The disease usually strikes middle-aged and elderly patients. Men are most affected between the ages of 50 and 60 years, while women are most affected between the ages of 60 and 70 years. Atypical and malignant meningiomas are more common in men. Meningiomas do not occur very often in children.

Causes and symptoms

Causes

Although no single factor has been found that causes meningiomas, several risk factors are known. Some patients have developed a meningioma after being exposed to radiation. These patients tend to be younger than typical meningioma patients, and their tumors often grow more quickly.

There is also a genetic component to meningioma. Patients who suffer from neurofibromatosis, a rare genetic disease, often develop multiple meningiomas.

Since meningioma cells recognize the female sex hormone progesterone, some researchers believe that female sex hormones may play a role in the development of meningiomas. This possible link is still being investigated.

Symptoms

Up to 75% of meningiomas produce no symptoms because they grow slowly and remain small. Often, tumors are discovered only when patients are being investigated for an unrelated illness. When symptoms do appear, it results that the tumor has grown large enough to compress part of the brain or spinal cord.

Patients experience different symptoms depending on the location of the tumor. Most brain meningiomas are located either just below the top of the skull, or between the two hemispheres of the brain. If the tumor is located in these areas, symptoms include:

• headaches
• seizures
• dizziness
• problems with memory
• behavior changes

More rarely, tumors are near sensory areas of the brain such as the optic nerve or close to the ears. Patients with these tumors experience vision or hearing losses.

Spinal meningiomas are usually found in the spinal column between the neck and the abdomen. The most common symptoms are:

• pain
• weakness and stiffness of the arms and legs
• episodes of partial paralysis