Tumors can be classified into four categories:
- Gliomas: These tumors occur in the glial cells, which help support and protect critical areas of the brain. Gliomas are the most common type in adults, responsible for approximately 42 percent of all adult brain tumors.
- Meningiomas: These tumors affect the meninges, the tissue that forms the protective outer covering of the brain and spine. One-quarter of all brain and spinal tumors are meningiomas, and up to 85 percent of them are benign. Meningiomas can occur at any age, but the incidence increases significantly in people over age 65. Women are twice as likely as men to have meningiomas. They generally grow very slowly and often don't produce any symptoms.
- Acoustic neuroma/schwannomas: Schwann's cells are found in the sheath that covers nerve cells. Vestibular schwannomas, also known as acoustic neuromas, arise from the eighth cranial nerve, which is responsible for hearing. Specific symptoms of vestibular schwannoma include buzzing or ringing in the ears, one-sided hearing loss and/or balance problems. Schwannomas are typically benign and respond well to surgery.
- Medulloblastoma: This a common brain tumor in children, usually diagnosed before 10 years of age. Medulloblastoma occurs in the cerebellum, which has a crucial role in coordinating muscular movements. Tumors grow quickly and can invade neighboring portions of the brain, as well as spreading outside the central nervous system. Medulloblastoma is slightly more common in boys.
Benign or Malignant Tumors
Benign brain tumors do not contain cancer cells. Usually, these tumors can be removed, and they seldom grow back. The border of a benign brain tumor can be clearly seen. Cells from benign tumors do not invade tissues around them or spread to other parts of the body. However, benign tumors can press on sensitive areas of the brain and cause serious health problems. Unlike benign tumors in most other parts of the body, benign brain tumors are sometimes life threatening. Very rarely, a benign brain tumor may become malignant.
Malignant brain tumors contain cancer cells. They're generally more serious and often are life threatening. They're likely to grow rapidly and crowd or invade the surrounding healthy brain tissue. Very rarely, cancer cells can break away from a malignant brain tumor and spread to other parts of the brain, the spinal cord, or other parts of the body.
Sometimes, a malignant tumor does not extend into healthy tissue. The tumor might be contained within a layer of tissue. Or, the bones of the skull or another structure in the head might confine it. This kind of tumor is called encapsulated.
Doctors group brain tumors by grade — from low grade (grade I) to high grade (grade IV). The grade of a tumor refers to the way the cells look under a microscope. Cells from high-grade tumors look more abnormal and generally grow faster than cells from low-grade tumors.