There are two broad categories of brain tumors: tumors which occur elsewhere in the body and metastasize to the brain, and tumors which arise from the tissues of the brain itself and its surrounding membranes. Cancer of the lung and breast, as well as melanoma, frequently metastasizes to the brain. Their treatment and prognosis is different from primary brain tumors.
All of the tissues of the brain may give rise to benign and malignant tumors. By far the most common cell of origin is the glial cell, producing gliomas. Gliomas are further subdivided into more specific cell types: oligodendroglioma, pilocytic astrocytoma, astrocytoma, and ependymoma. These tumors range from an extremely a benign tumor which may not progress, pilocytic astrocytomas, to the most malignant of brain tumors, the glioblastoma multiforme.
WHO Classification of Gliomas
Grade 2 diffuse astrocytoma
The glial cells are the supporting cells of the brain, forming the structure holding and nourishing the nerve cells and their processes. They are the most common cells of the brain. Glial tumors may arise anywhere within the central nervous system including the optic nerves and spinal cord. Hence the symptoms caused by gliomas include dysfunction of any part of the CNS. Generally speaking, gliomas present with symptoms of focal dysfunction of the brain: weakness, numbness, visual loss. Tumors which begin in "silent areas" of the brain can become very large before the patient develops symptoms of mass-effect from increased pressure within the head: headache and lethargy. Gliomas can irritate the brain and produce seizures. Rarely gliomas may spontaneously hemorrhage, presenting as a stroke.
The diagnosis of gliomas is usually straightforward. The tumors are imaged by MRI scanning using intravenous contrast dye. MR spectroscopy (MRS) is a technique which may add to diagnosis by providing clues about the chemical nature of the tumor. The imaging characteristics usually do not confirm a diagnosis with certainty. For example, the image characteristics of a glioblastoma is similar to that of a brain abscess. The gold standard for diagnosis is a brain biopsy. The biopsy may be excisional, by open operation on the brain, or stereotactic, using a small, guided probe to sample a small amount of tissue. The microscopic appearance of biopsied tissue, aided by special tissue stains, usually produces a definitive diagnosis. Accurate diagnosis allows accurate advice for treatment options and an estimate of overall prognosis.
The treatment of gliomas is evolving. Low-grade tumors which are not growing and causing progressive symptoms need no treatment. Malignant gliomas cannot be totally removed by surgery and require additional treatment. The most effective treatment is radiation therapy which can slow or stop tumor progression for a period of time. Recent advances in chemotherapy for malignant gliomas with temozolomide have extended survival. Other established chemotherapeutic protocols and experimental protocols may be useful. Local irradiation with radioactive Iodine-125 (Gliasite Balloon) at the initial time of surgery or with tumor recurrence may be fruitful. Radiosurgical boost of tumor re-growth and re-operation are additional tactics used to treat tumor progression after initial radiation therapy.