Tumor by definition
Brain tumors for simplicity can be defined as a group of similar cells that do not follow normal cell division and growth and represents itself as mass of cells or space occupying lesions.
They are not only created by brain itself only, but also in lymphatic tissue, in blood vessels, in the cranial nerves, in the brain coverings (meninges), skull bones, pituitary gland, or pineal gland.
Brain tumors may also spread from cancers primarily located in other organs which are called metastaic tumors.
Any brain tumor is serious and life-threatening because of its compressive, invasive and infiltrative character in the limited space of the skull cavity.
However, not all brain tumors (even malignant ones) are invariably fatal. Brain tumors can be cancerous (malignant) or non-cancerous (benign); however, the definitions differs from those commonly used in other types of neoplasms in the body.
Its prognosis depends on the combination of factors like the type of tumor, its location, its size and its duration of development.