Gliomatosis cerebri is a type of malignant (cancerous) brain tumor called a glioblastoma that develops from a specific type of brain cell called an astrocyte. It involves at least three sections (lobes) within the main part of the brain (cerebrum). It may also affect both sides of the cerebrum as well as the nerve cells within the brain (grey matter). There are two types of Gliomatosis cerebri. Type 1 (classic form) is characterized by scattered and widespread tumor cells and no apparent mass or tumor, while type 2 has similar characteristics in addition to a detectable mass or tumor. Signs and symptoms of Gliomatosis cerebri may include personality changes, memory disturbance, headaches, and seizures.