Brain

Germ cell tumors (GCTs) arise from primordial germ cells that did not migrate appropriately during embryonic development.   Residual primordial germ cells deposited in the brain give rise to intracranial germ cell tumors.  These residual primordial germ cells tend to be located in the midline of the body; therefore intracranial germ cell tumors typically originate in the suprasellar or pineal region.  Rarely GCTs originate in other midline intracranial locations including the basal ganglia, thalamus, and ventricles.  Intracranial germ cell tumors are twice as likely to be located in the pineal region compared to the suprasellar region.  Approximately 5-10% of cases have “bi-focal” disease, defined as simultaneous involvement of the suprasellar and pineal region.  Intracranial germ cell tumors mainly occur in adolescents and young adults (peak incidence is 10-12 years of age) and are more commonly seen in boys.  These tumors have the capacity to spread (metastasize) through the spinal fluid (leptomeningeal spread).

Medulloblastoma (also referred to as primitive neuroectodermal tumor or PNET) arises from the primitive or embryonal cells of the cerebellum. Medulloblastoma is a tumor that arises within the cerebellum and often grows into the fourth ventricle. These tumors have the capacity to spread (metastasize) through the spinal fluid (leptomeningeal spread), occurring in approximately 30% of cases, and they rarely spread to bone and bone marrow.

An ependymoma is a tumor that arises from the ependymal cells, which line the ventricles of the brain and the central canal of the spinal cord.  Ependymomas are typically found in three major locations: the posterior fossa, the supratentorium, and the spinal cord.  Over 90% of ependymoma arise from the brain and 10% arise for the spinal cord.  Ependymomas rarely spread (metastasize) from their site of origin.

DNET or Ganglioglioma are slow growing tumors that are composed of both glial and neuronal elements.  They are very rare, accounting for less than 1-2% of brain tumors.  They typically develop from the supratentorial region, mainly the temporal lobe or frontal lobe.  Ganglioglioma are rarely located in other areas of the brain and spinal cord.  These tumors do not have a capacity to metastasize or spread beyond the primary site of origin.  DNET and Ganglioglioma are indolent, slow-growing tumors.  Very rarely ganglioglioma will undergo malignant transformation.  These tumors are mainly seen in children and young adults.  The average age of diagnosis is 9 years of age.  There is no known cause for DNET and Ganglioglioma.

A craniopharyngioma is a benign tumor arising from squamous cell and is found along the path of the primitive craniopharyngeal duct and adenohypophysis.  Craniopharyngiomas are located intracranially but outside the brain, near the anterior base of the cerebrum, in a location termed the sella and suprasellar region.  Craniopharyngiomas will frequently grow to involve the third ventricle, hypothalamus, optic chiasm and pituitary gland.  A Craniopharyngioma is classified as a benign tumor, but its impact can be significant due to its location near critical structures.

Cerebellar Juvenile Pilocytic Astrocytoma (JPA) makes up about 15-25 percent of brain tumors seen in children. This type of tumor arises from an astrocyte, which is a type of glial cell.  Astrocytes make up the supportive tissue of the brain.  Astrocytes are named for their star-like appearance.  Cerebellar astrocytomas arise from the cerebellum, which is the area of the brain responsible for controlling coordinated movement, balance and posture.  Cerebellar JPA tend to occur before the age of 10 years, most commonly between the ages of 6 and 9 years of age.  Patients with cerebellar JPA have an excellent prognosis.

Brainstem gliomas make up approximately 10-20% of all central nervous system tumors of childhood. They typically occur in children less than 10 years of age. Brainstem gliomas arise from glial cells within the brain stem. Glial cells are a type of support tissue cell. The behavior, treatment and prognosis of a brainstem glioma are determined by where it is located within the brainstem (midbrain, pons, medulla), how it grows within the brainstem (diffuse or focal and intrinsic or exophytic), and the type of glioma (low grade or high grade). The brainstem is composed of three main parts: midbrain, pons and medulla. Brainstem gliomas can arise in any area of the brainstem, but the pons is the most common location making up 75-85% of brainstem tumor.  Brainstem gliomas typically grow in a diffuse fashion among the normal cells within the brainstem, making it impossible to remove the tumor without injuring the normal brainstem.  These tumors are termed “diffuse intrinsic”, have a more aggressive pathology (high grade), and have a poor prognosis.  Diffuse intrinsic brainstem tumors commonly arise within the pons and rarely within the medulla.  Some brainstem gliomas develop within the brainstem (intrinsic) but grow in a focal fashion and are termed “focal intrinsic” brainstem gliomas.  Focal intrinsic brainstem gliomas are typically located in the medulla or midbrain. Focal brainstem gliomas can also develop in an exophytic fashion (i.e. growing from the edge of the brainstem with the majority of the tumor protruding outside of the brainstem). Focal intrinsic and exophytic brainstem gliomas tend to have a less aggressive pathology (low grade), can often be surgically removed, are typically responsive to chemotherapy and radiation therapy, and usually have a good prognosis.

Astrocytoma, also called glioma, is the most common brain tumor, accounting for more than half of all Central Nervous System (CNS) malignancies. These tumors originate from astrocytes, which are star-shaped brain cells. Astrocytes are a type of glial cell which function to support the surrounding cells. Astrocytomas typically occur in the first decade of life with the peak age of occurrence at 5-9 years.

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