Cancers of the brain are the consequence of abnormal growths of cells in the brain. Brain cancers can arise from primary brain cells, the cells that form other brain components (for example, membranes, blood vessels), or from the growth of cancer cells that develop in other organs and that have spread to the brain by the bloodstream (metastatic brain cancer).
Although many growths in the brain are popularly called brain tumors, not all brain tumors are cancerous. Cancer is a term reserved for malignant tumors.
Malignant tumors grow and spread aggressively, overpowering healthy cells by taking their space, blood, and nutrients. Like all cells of the body, tumor cells need blood and nutrients to survive. This is especially a problem in the brain, as the added growth within the closed confines of the skull can lead to an increase in intracranial pressure or the distortion of surrounding vital structures, causing their malfunction.
Tumors that do not grow aggressively are called benign. Almost all tumors that begin in the brain do not spread to other parts of the body. The major difference between benign and malignant tumors is that malignant tumors can invade the brain tissues and grow rapidly. This rapid growth in the confines of the skull can quickly cause damage to nearby brain tissue.
In general, a benign tumor is less serious than a malignant tumor. However, a benign tumor can still cause many problems in the brain, but usually the problems progress at a slower rate than malignant tumors.
Sometimes people confuse brain aneurysms with brain tumors. Brain aneurysms are not tumors; they are areas in the brain arteries or veins that are abnormally weak and expand to form a ballooning or expansion of the vessel wall. They seldom produce any symptoms unless they begin to leak blood into the surrounding brain tissue. Aneurysms may be congenital (present at birth) or expanded or formed in brain vessels after vessel damage (for example, trauma, atherosclerosis, high blood pressure) but are not formed from cancer cells. Unfortunately, when aneurysms produce symptoms, they can resemble those produced by brain tumors