Brain tumors are divided into two different categories, meningiomas and gliomas. Ninety percent of meningiomas are benign. This means that they are not cancerous and surgeons can easily remove them because it is mainly made up of cells that cover the brain. However, sometimes these tumors can grow so large that they press up against the brains ventricular system, which leads to potentially fatal consequences. Gliomas, the other type of tumors, are divided into two main types, astrocytic and oligodendroglial tumors. Gliomas are the worst kind of brain turmos because they are very aggressive and tend to spread about the brain very quickly.