There are two main types of brain tumors: primary brain tumors that originate in the brain, and metastatic brain tumors that originate from cancer cells that have come from other parts of the body. Primary tumors can be either benign (noncancerous) or malignant (cancerous). Malignant tumors in the brain are life-threatening, because they are aggressive and invasive in nature.
Slow-growing benign tumors in the brain also can have life-threatening consequences, depending on the type of tumor and its location. This is because the skull is a closed, and when a brain tumor takes up space, it can compress vital tissues and structures and cause serious neurological problems. Some brain tumors are easier to remove and treat than others.
Brain tumors are classified according to the type of cell that makes up the tumor, or the cell type from which the tumor originated. Gliomas are tumors that are made up of glial cells (cells that provide important structural support for the nerve cells in the brain). An astrocyte is one type of glial cell, and the tumors that grow out of astrocytes are called astrocytomas.
Meningiomas are tumors of the meninges, the membranes covering the brain. Pituitary adenomas are tumors that start in the anterior pituitary (gland at the base of the brain that secretes hormones important for growth and reproduction).
Lymphomas are tumors made up of lymph cells (lymph is a fluid that flows through all the tissues of the human body and plays an important role in cleaning out bacteria and other foreign matter). Metastic tumors are brain tumors that have originated elsewhere in body and have metastasized to the brain. In addition to being classified on the basis of cell type, malignant tumors are typically assigned a tumor grade, based on what the cancer cells look like under a microscope.
Primary Brain Tumors
Gliomas are tumors that are made up of glial cells, cells that play an important structural role in the brain. There are several types of gliomas and the two most common are astrocytomas, cancerous tumors, and oligodendrogliomas - rare, usually benign tumors. A particularly malignant type of astrocytoma is known as a glioblastoma multiforme, which can be either low grade (slow-growing and not very aggressive) or high grade (fast-growing and very aggressive).
About 25 percent of all brain tumors are astrocytomas, malignant tumors that originate in cells called astrocytes. Astrocytomas are graded and named based on what the cells look like under the microscope. Low-grade astrocytomas are made up of the least aggressive cancer cells, anaplastic astrocytomas are made up of more aggressive cancer cells, and a glioblastoma multiforme is a type of astrocytoma that is made up of extremely aggressive cancer cells. Glioblastoma multiforme is the most common adult primary tumor.
Astrocytomas usually develop between the ages of 20 to 50, but they can occur at any age. One of the most common early symptoms is seizures. Although they can develop anywhere in the brain, they usually develop in the temporal or frontal lobes of the brain and then spread into the adjacent tissues.
Glioblastoma multiforme, a type of malignant astrocytoma, are the most common adult primary brain tumors. They occur slightly more frequently in men. Patients with these types of tumors are usually over the age of 50, but the tumors can develop at any age. Patients who develop the tumor at a younger age have a significantly better survival rate than older patients. Symptoms are caused by rapid tumor growth, infiltration into adjacent tissues, swelling (edema) and an increased accumulation of cerebrospinal fluid in the brain (hydrocephalus). Most patients experience headaches, seizures, or a change in their mental status.
Fewer than 5 percent of all brain tumors are oligodendrogliomas, tumors that originate in cells called oligodendrocytes. The average age of patients with these kinds of tumors is arbout 40 years old. Oligodendrogliomas are very slow-growing, usually benign tumors (less than 10 percent are malignant), and they occur most often in the frontal lobes. The first symptom for many patients is a seizure.
There are two types of oligodendrogliomas: low-grade oligodendrogliomas are made up of less aggressive cells, and anaplastic oligodendrogliomas are made up of more aggressive cells. More common than either low-grade or anaplastic oligodendrogliomas, however, are tumors made up of a mix of oligodendrioglioma and astrocytoma. These mixed-cell tumors are called oligoastrocytomas.
Fewer than 5 percent of all brain tumors are ependymomas, which usually occur in the lining of the ventricles, the structures in the brain that contain the cerebrospinal fluid. They also occur in the lining of the middle part of the spinal cord. One of the earliest symptoms is hydrocephalus, an increased accumulation of cerebrospinal fluid that causes swelling and neurological dysfunction.
The pituitary gland is a small structure at the base of the brain that produces hormones necessary for normal growth and metabolism. Tumors in the pituitary gland are called pituitary adenomas, benign tumors that account for about 10 to 20 percent of all brain tumors.
There are two types of pituitary adenomas: secreting and nonsecreting. A patient with a secreting pituitary adenoma has abnormally high levels of pituitary hormones circulating through their body, which in turn causes a range of symptoms from impotence (ED, erectile dysfunction) to amenorrhea (the abnormal ending of menstruation). For example, one of the more common types of pituitary adenomas produces and secretes excess prolactin, a substance responsible for triggering milk production when a woman is nursing.
In addition, because the pituitary gland is located near important visual pathways, a patient with a pituitary adenoma may experience vision loss.
The meninges is the thin outer covering that lines the spinal cord and brain. It is made up of three layers: the dura matter (external), the arachnoid (middle) and the pia matter (internal). Tumors that originate in the meninges are called meningiomas.
About 15 to 20 percent of all brain tumors are benign, slow-growing meningiomas. Even though they are benign, they can still cause severe neurological dysfunction. Patients often suffer seizures, headache, weakness, and visual problems. They occur more commonly in women and after the age of 40. Patients with neurofibromatosis, a genetic disorder that predisposes to certain types of tumors, are at a greater risk for developing meningioma. Patients who have had previous brain radiation are also at a greater risk for developing meningioma. Many patients with meningiomas seem to have a genetic defect on chromosome number 22.
Nerve Sheath Tumors (Schwannomas)
Nerve sheath tumors, also known as schwannomas, are tumors that originate in the Schwann cells that make up the protective sheath that surrounds the nerve fibers. Schwannomas are usually benign and slow-growing. One of the most common types is known as a vestibular schwannoma, or acoustic neuroma. Another common schwannomas causes facial paralysis.
Acoustic neuromas are schwannomas that involve the eighth cranial nerve. There are a total of 12 pairs of cranial nerves that originate in the brainstem (the bottom part of the brain that connects to the spinal cord) and lead to various parts of the face and neck. The eighth cranial nerve is responsible for balance and hearing. Acoustic neuromas cause early hearing loss in the ear on the side of the tumor, tinnitus (ringing in the ears), vertigo (dizziness), balance problems, and facial weakness. These tumors occur most commonly in people between 30 and 50 years old but can occur anytime.
Metastatic Brain Tumors
Cancerous tumors that spread to the brain from other parts of the body, such as the lung, are said to be metastatic. Tumor cells spread to the brain through the bloodstream. In more than half of all metastatic brain cancer, the tumors are found throughout the brain and are not localized to one particular spot, making them extremely difficult to treat. Between 20 and 40 percent of all cancer patients develop metastases to the brain. In adults, the most common types of cancer to spread to the brain are lung, breast, gastrointestinal, and urinary/genital tract cancer, as well as malignant melanoma.
The main symptoms of metastatic brain tumors include seizures, headaches, weakness and confusion. In general, the prognosis for patients who develop brain metastases is poor.
Spinal Cord Tumors
Primary spinal cord tumors are very rare and usually benign. Only about 1 in 200 newly diagnosed NS tumors are spinal cord tumors. Of these, fewer than 3 percent are malignant, or cancerous. Spinal cord tumors are made up of the same types of cells that make up brain tumors. For example, they include meningiomas and gliomas. Most malignant spinal cord tumors, again of which there are very few, are tumors that originate from cancer cells that come from other parts of the body.
The spinal cord has only a limited amount of space inside the spinal column (the backbone or spine), so even a very small tumor can cause enough pressure to become problematic. Though sometimes the tumor grows so slowly that the spinal column is able to adapt to it and make room for it such that a person suffers very few symptoms. Very aggressive metastatic spinal cord tumors can cause paralysis very quickly - even within days. Slow-growing tumors can also cause paralysis if left untreated.
Surgery is the usual course of treatment for primary spinal cord tumors. Metastatic spinal cord tumors are not always treated surgically, however, especially if there is more than one metastasis. Although often surgery may be used as a way to relieve pain and other symptoms, even though it may not actually involve removing the tumor.