There are many types of brain tumors, which can be classified in a number of ways. The classification of brain tumors involves a number of diagnostic tests that can include blood tests, imaging tests and biopsies. Initially, tumors in the brain are typically classified into two categories: primary and metastatic (secondary).

Primary brain tumors are less common and have the following characteristics:

• Develop from cells within the central nervous system (CNS)
  
  
• Can be benign (noncancerous) or malignant (cancerous)
  
  
• Are more often malignant than benign
  
  
• Rarely spread from the brain to distant areas or organs
  
  
• Damage results from the cancer spreading to nearby tissues causing pressure due to lack of space for expansion inside the skull
  

The National Cancer Institute (NCI) reports that in general, primary brain tumors occur more often in whites than African Americans. In addition, the mortality or death rate is higher in males than females.

Metastatic or secondary brain tumors are more common and have the following characteristics:

• Result from cancer that has started elsewhere in the body and spread cancer cells to the brain
  
  
• Secondary tumors are always cancerous and never benign
  
  
• Prognosis varies with age of patient, location of tumor in brain and response to treatment

According to the NCI, the most common primary cancers that metastasize to the brain are as follows:

The next important classification of a primary brain tumor is whether the growth is malignant or benign. These two groups are radically different because benign tumors are not cancerous, whereas malignant tumors are cancerous. Characteristics of the groups include:

• Benign tumors:
  
  
• Do not contain cancer cells
• Slow growing, easier to remove
• Once removed, usually do not recur
• Do not usually invade surrounding tissues
• May cause same symptoms as malignant tumors depending on size and location in the brain
  
  
• Malignant tumors:
  
  
• Contain cancer cells
• Usually fast growing
• Can invade surrounding tissues
• Rarely spread to other areas of the body
• Often recur after treatment

There are many types of brain tumors, although certain types occur more often than others.

Brain tumors belonging to the family called gliomas are the most common type of tumors. Glioma is not a specific cancer but a general category that includes a number of types of brain tumors. These tumors begin in the glial cells, which are found in the supportive tissue of the brain. Gliomas are categorized by their location and the type of cells that originated the tumor. Gliomas include the following tumors:

• Astrocytomas. These tumors start in brain cells called astrocytes. Astrocytomas are the most common type of primary brain tumor in adults. Astrocytomas are classified as low, intermediate or high grade based on a biopsy of tissue from the tumor. The grade of the tumor determines how quickly the tumor grows and the prognosis for recovery. Low-grade tumors grow the slowest, and high-grade tumors grow the fastest. 
  
  Astrocytomas rarely spread outside of the brain or spinal cord, but they do tend to spread to surrounding tissues. Astrocytomas have a low cure rate.
   
  Anaplastic astrocytoma and glioblastoma are the most malignant and account for 38 percent of primary brain tumors, according to the NCI. Treatment and prognosis depend on the type of tumor.
  
  
• Oligodendrogliomas. These tumors begin in brain cells called oligodendrocytes, which nourish nerve cells. The pattern of spreading to tissues is similar to astrocytomas in that they rarely spread outside of the brain or spinal cord. In most cases, these tumors cannot be completely removed by surgery.
  
  
• Ependymomas. These tumors develop from the ependymal cells, which are found primarily in the lining of the spaces around the brain and spinal cord. These spaces hold cerebrospinal fluid, which protects the brain and spinal cord from injury. The tumors usually do not spread into the brain tissue or outside of the brain or spinal cord. However, they may spread along the spinal fluid pathways. These types of tumors are relatively rare and occur primarily in children.
  
  
• Mixed gliomas. These are brain tumors that contain more than one type of cell. The prognosis for recovery depends on the type of cells in the tumor and the grade of the most severe cell.
  
  
• Brain stem gliomas. These tumors develop from the cells located in the brain stem, which is the part of the brain closest to the spinal cord. These tumors occur almost exclusively in children and are often very aggressive cancers.

Other common types of primary tumors include the following:

• Meningioma. Meningiomas develop from the layers of tissue that surround the outer part of the brain and spinal cord. In the strictest sense, meningiomas are not brain tumors because they occur outside of the brain tissue, but they are classified as brain tumors. Characteristics include:
  
  
• Account for 20 to 40 percent of primary brain tumors
  
  
• Tend to occur during midlife and older ages
  
  
• Are more common in women
  
  
• Occasionally occur in families with history of Von Recklinghausen’s disease (neurofibromatosis)
  
  
• Small percentage are malignant and recur after surgery
  
  
• 85 percent are benign and can be cured, according to the American Cancer Society
  
  
• Medulloblastomas. These rare tumors develop from cells in the cerebellum. The tumors grow quickly and often spread to other areas of the central nervous system. However, they can be treated and often cured by radiation therapy. Although these tumors can occur in anyone, they are most commonly found in children.
  
  
• Germ cell tumors. These tumors arise from germ cells, which are normally found in the ovaries of women and testicles in men. The germ cells may travel to abnormal locations, such as the brain or spinal cord, during fetal development. Germ cell tumors can occur anywhere in the body and may be benign (noncancerous) or malignant (cancerous). The most common type of germ cell tumor found in the central nervous system is the germinoma. These types of tumors are very rare in adults and account for only a small percentage of tumors in children as well.
  
  
• Schwannomas. These tumors, also known as neurilemomas, develop from Schwann cells, which are located around the nerves in the brain. They are usually benign and often affect the nerves that control hearing and balance.
  
  
• Chordomas. These tumors develop in the bone at the base of the skull or at the end of the spinal cord. The tumors do not usually spread to other organs but typically return repeatedly over a 10- to 20-year period.
  
  
• Pineal parenchymal tumors. Pineal tumors form in the pineal gland, a small organ in the brain that produces the hormone melatonin. This hormone helps regulate an individual’s sleep and wake cycle. There are several different types of these tumors that can vary in severity. Pineocytoma occurs most often in adults aged 25 to 35. Pineoblastomas are rare and usually occur in children.
  
  
• CNS lymphoma. These tumors develop in lymphocytes (cells in the immune system) found in the CNS. In the past, brain lymphomas have been considered a very aggressive cancer resulting in death in about one year. Recent advances in treatment with chemotherapy have improved the prognosis for patients with brain lymphomas.