A brain tumor is a growth of cells in or near the brain. Brain tumors can occur in or near brain tissue. These nearby places include nerves, the pituitary gland, the pineal gland, and the membranes that cover the surface of the brain.

Brain tumors can start inside the brain and are called primary brain tumors. Sometimes, cancer from other parts of the body reaches the brain.

These tumors are called secondary brain tumors, and they are also called metastatic brain tumors.
Primary brain tumors have several different types. Some brain tumors are not cancerous and are called benign brain tumors.

Noncancerous brain tumors may grow over time and put pressure on brain tissue. Other types of brain tumors are brain cancers, also called malignant brain tumors. Brain cancers may grow quickly and cancer cells can invade and destroy brain tissue
. Brain tumors range in size from very small to very large. Some brain tumors are discovered when they are very small because they cause symptoms you notice right away. While other types of brain tumors grow to a very large size before they are detected. Some parts of the brain are less active than others. If a brain tumor starts in a less active part of the brain, it may not cause symptoms right away. The tumor may reach a very large size before it is discovered.

Types of brain tumors include:

Gliomas and related brain tumors: Gliomas are abnormal growths of cells that resemble glial cells. Glial cells are cells that surround and support nerve cells in brain tissue. Gliomas and related brain tumors include astrocytoma, glioblastoma, oligodendroglioma, and ependymoma. They can Gliomas are benign, but most are malignant, and glioblastoma is the most common type of malignant brain tumor.

Choroid plexus tumors: Choroid plexus tumors begin in the cells that secrete the fluid surrounding the brain and spinal cord. This fluid is called cerebrospinal fluid. Choroid plexus tumors are located in the fluid-filled cavities in the brain, called ventricles. Choroid plexus tumors can be benign or malignant. Choroid plexus carcinoma is the malignant form of this type of brain tumor and is more common in children.

Embryonic tumors: Embryonic tumors begin in the remaining cells of the developing fetus. These cells, called fetal cells, remain in the brain after birth. Embryonic tumors are malignant brain tumors that often occur in infants and young children. The most common type of embryonal tumor is medulloblastoma, which usually occurs in the lower back part of the brain called the cerebellum.

Germ cell tumors: Germ cell tumors begin in reproductive cells – also known as germ cells – that turn into sperm cells and egg cells. Germ cells are mostly found in the ovaries and testicles, but they are sometimes found in other parts of the body, such as the brain. When germ cell tumors occur in Brain, they often appear near the pineal gland or pituitary gland. Germ cell tumors are often benign. It is more common in children.

Pineal tumors: Pineal tumors begin in the pineal gland in the brain and around the gland. The pineal gland is located in the middle of the brain. It produces a hormone called melatonin that helps sleep. Pineal tumors can be benign or malignant. Pineoblastoma is a malignant type of pineal tumor that is more common in children.

Meningiomas: Meningiomas are brain tumors that begin in the membranes surrounding the brain and spinal cord. Meningiomas are mostly benign, but they can sometimes be malignant. Meningiomas are the most common type of benign brain tumor.

Nerve tumors: Nerve tumors are abnormal growths that occur in and around nerves. The most common type that occurs in the head is an acoustic neuroma, also called a schwannoma. This benign tumor occurs on the main nerve that connects the inner ear to the brain.

Pituitary tumors: Brain tumors can start in and around the pituitary gland, a small gland located near the base of the brain. Most tumors that occur in and around the pituitary gland are benign tumors, and pituitary tumors occur in the pituitary gland itself. Brain tumors that occur near the pituitary gland include craniopharyngioma.

Other brain tumors: Many other types of rare tumors can occur in and around the brain. These tumors may begin in the muscles, blood vessels, and connective tissue surrounding the brain. Tumors may form in the bones of the skull. Malignant brain tumors may begin from germ-resistant immune system cells in the brain. This type of brain cancer is called primary central nervous system lymphoma.