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 Introduction
Brain tumors are abnormal growths of cells located in the brain, or arising from the coverings of the brain. Tumors are generally separated into two categories: 1) primary brain tumors (those arriving within the head itself) or 2) metastatic tumors (tumors that spread from different areas of the body).
Primary brain tumors are differentiated based on the cell type from which they originate, including glial cells (cells that separate and support the central nervous system called astrocytes, oligodendrocytes, and ependymal cells), neuronal cells (nerve cells themselves), meningeal cells (cells that line the CNS), or Schwann cells (cells that line peripheral nerves).
Most primary brain tumors, specifically astrocytomas, are then further classified in a four stage grading system based on World Health Organization (WHO) criteria. Grading ranges from I (benign and surgically curable) to IV (malignant).
Currently, it is unclear as to why brain tumors occur. Although multiple large epidemiologic studies have been undertaken, no specific risk factors for tumor have been elucidated. The risk certainly increases with age, but otherwise no specific environmental or genetic factor has been linked to these tumors. The exception is prior therapeutic radiation, which has been shown to increase the risk of glioma and meningioma formation.
Primary brain tumors are diagnosed in about 17,000 patients every year of which 3,500 are in children under the age of 20. Metastatic tumors are much more common and are found in up 170,000 patients per year. All metastatic tumors are considered malignant, and the behavior of these tumors varies widely according to the type of tumor from which they arose. The most common types of metastatic tumors in order of frequency are: 1) lung cancer, 2) breast cancer, 3) renal cell cancer, 4) melanoma, and 5) colon cancer.
Types of Brain Tumors
 There are many types of CNS tumors and below are discussed some of the more common ones.
Astrocytoma: Astrocytomas arise from astrocytes, which line and support the CNS. These tumors vary in grade depending on their histologic features (determined by a pathologist who looks at the cells under a microscope). Low grade astrocytomas represent 15% of primary tumors, and tend to occur in patients in their 30's and 40's. The 10 year survival for low grade astrocytomas is around 50%.
GBM: The most common and most malignant type of astrocytoma is the grade IV astrocytoma, or Glioblastoma Multiforme (GBM). GBM's represent 25% of primary tumors, and are the most commonly diagnosed tumors in those aged 55 to 75. Average survival for these patients is about 13 months.
Oligodendroglioma: These tumors arise form oligodendrocytes, cells that produce myelin (the covering of nerve cell processes) in the CNS. Oligodendrogliomas account for 15-20% of primary tumors, and occur in two peaks, around the ages of 35 and 55. Survival is slightly better than astrocytomas.
Ependymoma: Ependymomas arise from the ependymal cells, which line the spinal fluid cavities inside the brain and spinal cord. These tumors occur in adults and children, and account for 2.5% of adult tumors. The 5 year survival for these tumors ranges from 40-60%.
Meningioma: Meningiomas arise from arachnoid cap cells along the dura (leathery covering over the brain and spinal cord). Meningiomas account for 25% of primary tumors, and increase in incidence with age. The vast majority of these tumors are benign and are curable with surgical resection. A significant number of these are treated successfully with radiosurgery.
Epidermoid/Dermoid: Epidermoids usually occur in the posterior fossa, and are benign lesions which form keratin. Dermoids are found in the midline of the CNS, and are usually associated with some form of dermal sinus (small connection to the skin) and include skin elements such as hair, sweat glands, and oil glands. Both of these types of tumors are curable with surgical resection.
Schwannoma: Schwannomas arise from Schwann cells, which make the myelin that covers the peripheral nerve, and account for 8-10% of primary tumors. The most common location for Schwannomas is on the eigth cranial nerve (Vestibular Schwannoma), while the next most common is on the fifth nerve. These tumors are almost always benign, and can be cured with surgical removal. Radiosurgery can successfully treat these lesions when they are small in size.
Symptoms
Symptoms of brain tumors depend on the location of the lesion but can include headaches, seizures, weakness or numbness on one side of the body, speech problems, or problems related to cranial nerves (including facial movement, hearing, vision, or swallowing). Symptoms are usually slow and progressive in nature.
Diagnosis
The diagnosis of a brain tumor is made using MR (magnetic resonance) imaging with and without contrast (image above shows a large ring enhancing tumor) .
Treatment
Decisions for treatment of brain tumors are made in a formal conference called the Brain Tumor Board. Surgeons, pathologists, and medical and radiation oncologists discuss each specific tumor and formulate a treatment strategy.
Treatment for primary brain tumors may include surgery, radiation, and chemotherapy. The mainstay of this treatment is surgical resection whenever possible, depending on the size and location of the tumor. Surgery involves an incision on the scalp, removal of bone over the area of tumor (craniotomy), and removal of the tumor. Most patients remain in the hospital for 2-3 days after surgery.
Tumors such as astrocytoma, GBM, and oligodendroglioma are infiltrative, and thus even with removal of all visualized tumor, microcopic disease will remain.
Radiation therapy may be used after surgery to address any remaining disease.
Chemotherapy is an evolving treatment for these lesions. In the past, only specific tumors such as anaplastic oligodendroglioma were good chemotherapy targets, however recent evidence suggest that Temodar (temozolomide) can extend survival in most glial type tumors.
One other treatment option, most often for benign lesions (meningioma, schwannoma) or metastatic tumors, is radiosurgery. This technique allows for a very high one time dose of radiation to be delivered to the tumor while sparing surrounding brain structures. This treatment is only acceptable for lesions that are less than 3cm in diameter, separate from the brain, and easily delineated on MRI or CT imaging.
Following treatment most patients with brain tumors will need serial MR brain imaging for several months to years to evaluate any recurrence.
The University of Florida is a leading center for brain tumor surgery in the Southeast US.
For additional information on brain tumor see the following links:
American Brain Tumor Association
Neuro-Onc.net
Neuro-Onc Links
Cancer.gov
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