Many brain tumors are cancerous. For example, more than half of all gliomas diagnosed in adults are glioblastomas, a very aggressive form of brain cancer. Ependymomas and oligodendrogliomas also are types of brain tumors that may be malignant. But not all brain tumors are cancerous. Many meningiomas, craniopharyngiomas and pituitary tumors are benign. That’s why it’s important to get a thorough and accurate diagnosis of a brain tumor. It’s also important to understand that even benign tumors can damage brain tissue and cause side effects, such as headaches, fatigue and double or blurred vision. So even if a brain tumor is not cancerous, receiving timely and appropriate treatment may be critical to your overall health.