Brain tumors, also known as brain cancer, start within the substance of the brain, spinal cord or nerves. Some tumors which arise from the brain or spine coverings (meninges) are also considered primary brain tumors. Metastatic brain tumors have spread from cancer in other parts of the body, most frequently from the lungs, breast and colon.
Depending on the location and size of the tumor, symptoms experienced by each patient may vary. Most of the common symptoms are due to increased intracranial pressure as the growing tumor affects surrounding structures:
- Frequent headaches (reported by 50% of patients)
- Blurry vision
- Nausea and/or vomiting
- Personality or cognitive changes
Other symptoms are site-specific, including seizures, speech impairment, weakness or numbness on one side and problems with coordination, balance or mobility.
Types of Brain Tumors
There are many
different types of brain tumors, based on what cells are affected and
how they appear under a microscope.
These tumors occur in the glial cells, which help support and protect critical areas of the brain. Gliomas are the most common type of brain tumor in adults, responsible for about 42% of all adult brain tumors. Gliomas are further characterized by the types of cells they affect:
Astrocytes
are star-shaped cells that protect neurons. Tumors of these cells can
spread from the primary site to other areas of the brain, but rarely
spread outside the central nervous system. Astrocytomas are graded from
I to IV depending on the speed of progression:
Grade I (pilocytic astrocytoma): slow growing, with little tendency to infiltrate surrounding brain tissue. Most common in children and adolescents.
Grade II (diffuse astrocytoma): fairly slow-growing, with some tendency to infiltrate surrounding brain tissue. Mostly seen in young adults.
Grade III (anaplastic/malignant astrocytoma): these tumors grow rather quickly and infiltrate surrounding brain tissue.
Grade IV (glioblastoma multiforme, GBM):
an extremely aggressive and lethal form of brain cancer. Unfortunately,
it is the most common form of brain tumor in adults, accounting for 67%
of all astrocytomas.
Oligodendrocytes
are cells that make myelin, a fatty substance that forms a protective
sheath around nerve cells. Oligodendrogliomas, which make up 4% of
brain tumors, mostly affect people over 45 years of age. Some subtypes
of this tumor are particularly sensitive to treatment with radiation
therapy and chemotherapy. Half of patients with oligodendrogliomas are
still alive after five years.
These tumors affect ependymal cells, which line the pathways that carry cerebrospinal fluid throughout the brain and spinal cord. Ependymomas are rare; about 2% of all brain tumors, but are the most common brain tumor in children. They generally don’t affect healthy brain tissue and don’t spread beyond the ependyma. Although these tumors respond well to surgery, particularly those on the spine, ependymomas cannot always be completely removed. The five-year survival rate for patients over age 45 approaches 70%.
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% 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. In fact, many meningiomas are discovered by accident. Meningiomas can be successfully treated with surgery, but some patients, particularly the elderly, may be candidates for watchful waiting to monitor the disease.
Schwannomas
Schwann’s cells are found in the sheath that covers nerve cells. Vestibular schwannomas, also known as acoustic neuromas, arise from the 8th 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 is a common brain tumor in children, usually diagnosed before the age of 10. These tumors occur in the cerebellum, which has a crucial role in coordinating muscular movements. Some experts believe that medulloblastomas arise from fetal cells that remain in the cerebellum after birth. 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.
Although many brain tumors can easily be seen with a CT scan or MRI, a stereotactic biopsy is sometimes needed to confirm the diagnosis and type of tumor. A special frame is attached to the patient’s head and adjusted to the tumor coordinates provided by a CT scan or other image of the brain. A small hole is drilled into the skull and a needle is inserted to obtain a sample of the tumor for inspection under a microscope. Advances in imaging technology have allowed stereotactic biopsies to be done without the frame.
Surgery is the most common treatment for brain tumors. However, with more aggressive brain cancers, complete removal of the tumor is not possible, and surgery is done to “debulk” or reduce the tumor as much as possible. Surgery may be combined with radiation therapy or followed with chemotherapy to destroy any remaining cancer cells. Radiation may also be used as a primary treatment for brain tumors in difficult or critical locations in the brain.
