Brain and Spinal Tumors Health Article

Definition

A brain tumor is an abnormal growth of cells (neoplasm) in the skull. A spinal tumor is a growth associated with the spinal cord. Tumors are classified as noncancerous tumors (benign tumors) or cancerous tumors (malignant tumors).

Description

Because the skull is a rigid structure that limits expansion, tumors (both benign and malignant) can exert destructive pressure on neural and support tissues. Although all brain tumors are contained within the rigid skull, tumors can exist within brain tissue (intracranial tumors) or as tumors associated with the outer surface of the brain.

Primary tumors

Tumors that initially arise and grow within the brain are termed primary tumors. Most adult brain cancers are not primary tumors, but are the result of primary cancer that has spread from other areas of the body. Most brain tumors in children, however, are primary tumors. The cells that nourish and support the neurons that compose the brain are most often those cells that exhibit the uninhibited division and growth that results in primary tumor formation. A glioma is a tumor that originates in the cells supporting and nourishing brain neural tissue (glial cells). The most common primary brain tumors include gliomas such as astrocytomas, ependymomas, and oligodendrogliomas.

Primary tumors are sometimes associated with specific genetic diseases such as tuberous sclerosis or neurofibromatosis. Tumors can also arise following exposure to a sufficient dosage to carcinogens (cancer-causing chemical substances) or nuclear radiation.

The most observed form of primary brain tumor found in adults within the general population are diffuse fibrillary astrocytomas that are then divided on the basis of microscopic examination of the tissue (histopathologic diagnosis) into three specific WHO (World Health Organization) grades of malignancy: grade II astrocytomas, grade III anaplastic astrocytomas, and grade IV glioblastoma multiform.

Pilocytic astrocytomas are the most common astrocytic tumors found in children. Desmoplastic cerebral astrocytoma of infancy (DCAI) and desmoplastic infantile ganglioglioma (DIGG) are present as large, superficial, usually benign astrocytomas that most commonly affect children under the age of two years.

Other gliomas and astrocytomas include brainstem gliomas (usually found in children) that are a form of diffuse, fibrillary astrocytoma that often follow a malignant course. The pleomorphic xanthoastrocytomas (PXA) are low-grade astrocytic tumors that are often found in young adults.

Subependymal giant cell astrocytomas (SEGA) are a form of periventricular, astrocytic tumor that are usually benign or low grade.

Other benign tumors include meningioma tumors (a fairly common, usually benign class of intracranial tumor affecting the meninges), epidermoid tumors, dermoid tumors, hemangioblastomas (usually benign tumors that occur most frequently in the cerebellum and spinal cord of young adults), colloid cysts, pleomorphic xanthoastrocytomas, craniopharyngiomas, and schwannomas. Schwannomas are not strictly a brain or spinal tumor because they arise on peripheral nerves—but they do grow on cranial nerves, particularly the vestibular portion of the acoustic nerve.

Other tumor forms related to diffuse, fibrillary astrocytomas include oligodendrogliomas and oligoastrocytomas. These cerebral tumors are, however, less common than astrocytomas.

Ependymoma tumors are gliomas that are unpredictable. Ependymomas found in the ventricles can be aggressive and highly destructive; other ependymomas are benign spinal cord tumors. Transformation of ependymomas to more malignant forms is rare.

Tumors of the choroid plexus tumors are also unpredictable. Occurring in the choroids plexus that line most of the ventricular system, they can result in the overproduction of cerebrospinal fluid. As with ependymomas, some are malignant, while others are benign.

Other tumors that are usually malignant include medulloblastomas (a highly malignant tumor usually found in children), atypical meningiomas, and hemangiopericytomas (tumors of the dura that may become aggressive and metastasize.)

Brain and spinal tumors are sometimes associated with diseases or disorders. For example, multiple hemangioblastomas are associated with von Hippel-Lindau disease (VHL), an inherited tumor syndrome. Neurological tumor syndromes are those in which patients are genetically predisposed and, therefore, at an increased risk for developing multiple tumors of the nervous system.