Q. What is a brain tumor? A. A brain tumour is any intracranial tumor normally either in the brain itself in the cranial nerves, in the brain envelopes, skull, pituitary and pineal gland, or spread from cancers primarily located in other organs (metastatic tumors). It is created by abnormal and uncontrolled cell division. Primary (true) brain tumors (which start in the brain) are commonly located in the posterior cranial fossa in children and in the anterior two-thirds of the cerebral hemispheres in adults, although they can affect any part of the brain.