Brain Tumor Classification

The term brain tumor is a generic one, describing a wide variety of entities. These span the range of biological behavior,from totally benign to malignant. Therefore the categories should be examined separately.

Brain tumors may be classified in several different ways. The most commonly used scheme is according to the cell of origin. Another approach is by the location of the tumor. In practice, both are important. The cell type (known as histology) determines the biologic behavior of the tumor and has a great bearing on the prognosis. The location of the tumor determines the symptoms and neurologic deficits produced, as well as the safety of its resectability, if it may be resected at all.

No single classification by cell type is universally agreed upon. This mayseem surprising, but this is because often the appearance of a tumor under the microscope bears little resemblance to normal cells. The cell of origin must be presumed. Most classification schemes are variants of the World Health Organization (WHO) classification, which may be summarized as follows:

1. Tumors arising from brain tissue
    
   1. Astrocytoma
       
      1. Pilocytic astrocytoma
      2. Low grade astrocytoma
      3. Anaplastic astrocytoma
      4. Glioblastoma multiforme
          
   2. Oligodendroglioma
       
   3. Ependymal and choroid plexus tumors
       
      1. Ependymoma
      2. Anaplastic (malignant) ependymoma
      3. Myxopapillary ependymoma
      4. Subependymoma
      5. Choroid plexus papilloma
      6. Anaplastic (malignant) choroid plexus papilloma

      The above tumor types (astrocytoma, oligodendroglioma, and ependymoma) are referred to as gliomas.

   4. Tumors arising from neurons
       
      1. Ganglioglioma
      2. Gangliocytoma
      3. Central neurocytoma
          
   5. Pineal cell tumors
       
   6. Embryonal tumors
       
      1. Primitive neuroectodermal tumor (PNET)
      2. Medulloblastoma (or PNET of posterior fossa)
          
2. Tumors of nerves
    
   1. Schwannoma
   2. Neurofibroma
       
3. Tumors of the coverings of the brain (meninges)
    
   1. Meningioma
       
4. Germ cell tumors (embryologically derived cell types)
    
   1. Germinoma
   2. Others: embryonal carcinoma,choriocarcinoma, teratoma
       
5. Other malformative tumors and tumor-like lesions
    
   1. Craniopharyngioma
   2. Rathke's cleft cyst
   3. Epidermoid and Dermoid cyst
   4. Colloid cyst of the third ventricle
   5. Lipoma
   6. Hamartoma
       
6. Tumors of the pituitary gland
    
7. Metastatic tumors to brain from elsewhere in the body