a tumor is an abnormal mass of tissue that's formed by an abnormal accumulation of cells. normally the cells in your body age die and are replaced by new cells. with cancer and other tumors something disrupts this cycle. new cells are made when they're not needed and old cells don't die. as this process goes on the tumor continues to grow as more and more cells are added to the mass. primary brain tumors emerge from the various cells that make up the brain and central nervous system and are named for the kind of cell in which they first form. the most common types of adult brain tumors are gliomas or astrocytic tumors. these tumors form from astrocytes and other types of glial cells which are cells that help keep nerves healthy. the second most common types of adult brain tumors are meningeal tumors. these form in the meninges the thin layer of tissue that lines the brain and spinal cord and can grow from a number of different kinds of brain and spinal cord cells.
what is a brain tumor?