This fluid circulates in the narrow spaces between cells and through the cavities in the brain called ventricles, to support and protect the brain tissue. Blood vessels enter the central nervous system through the perivascular space above the pia mater. The cells in the blood vessel walls are joined tightly, forming the blood–brain barrier which protects the brain from toxins that might enter through the blood. Tumors of the meninges are meningiomas and are often benign. Though not technically a tumor of brain tissue, they are often considered brain tumors since they protrude into the space where the brain is, causing symptoms. Since they are usually slow-growing tumors, meningiomas can be quite large by the time symptoms appear. Brain matter The brains of humans and other vertebrates are composed of very soft tissue and have a gelatin-like texture. Living brain tissue has a pink tint in color on the outside (gray matter), and nearly complete white on the inside (white matter), with subtle variations in color. The three largest divisions of the brain are: Cerebral cortex Brainstem Cerebellum These areas are composed of two broad classes of cells: neurons and glia. These two types are equally numerous in the brain as a whole, although glial cells outnumber neurons roughly 4 to 1 in the cerebral cortex. Glia come in several types, which perform a number of critical functions, including structural support, metabolic support, insulation, and guidance of development. Primary tumors of the glial cells are called gliomas and often are malignant by the time they are diagnosed. The thalamus and hypothalamus are major divisions of the diencephalon, with the pituitary gland and pineal gland attached at the bottom; tumors of the pituitary and pineal gland are often benign. The brainstem lies between the large cerebral cortex and the spinal cord. It is divided into the midbrain, pons, and medulla oblongata. Spinal cord The spinal cord is considered a part of the central nervous system. It is made up of the same cells as the brain: neurons and glial cells. Diagnosis Although there is no specific or singular symptom or sign, the presence of a combination of symptoms and the lack of corresponding indications of other causes can be an indicator for investigation towards the possibility of a brain tumor. Brain tumors have similar characteristics and obstacles when it comes to diagnosis and therapy with tumors located elsewhere in the body.