BRAIN TUMORS

Primary brain tumors

Primary brain tumors include those arising from the various cell types within the brain tissue:

• Gliomas and Astrocytomas¹ are tumors that arise from the glial cells² and are typically classified as grade 1 thru grade 4 dependent on their rate of growth and vascularity ³ as well as other factors.

• Oligodendrogliomae⁴ are tumors that arise from the oligodendrocytes in the brain and typically are slow growing tumors and will have a more favorable outcome.

• Ependymomas ⁵ are tumors arising from the cells lining ventricular cavities of the brain. These tumors also tend to have a more benign course and a more favorable outcome.

Metastatic brain tumors

Metastatic ⁶ tumors are those tumors arising outside the nervous system in areas such as the lung or other organs, and will often spread to the brain through the blood stream, forming a growth within the substance of the brain or within the skull base. These tumors may be treated surgically in combination with radiation therapy, or with radiation therapy alone, which may consist of either whole brain radiation or cyberknife radiosurgery ⁷.

Tumors of the skull base and meninges ⁸

These tumors are often referred to as extra axial tumors , since they arise outside the substance of the brain.

• Meningioma is a typical example of an extra axial tumor over the surface of the brain, or along the base of the skull under the brain. These may also be referred to as skull base tumors, particularly when they invade the base of the skull.

• Acoustic neuroma is another skull base tumor that arises from the 8 th cranial nerve (auditory, or hearing) as it enters the skull base. These are typically benign tumors that can be managed surgically, with radiosurgery, or a combination of the two depending on the circumstances.

• Epidermoid tumors are benign, usually arising around the base of the brain. They can be managed surgically, but are not responsive to radiation therapy.

• Craniopharyngiomas are tumors found more often in children than in adults. They arise in the pituitary gland or 3 rd ventricle, and can grow to a very large size before discovered. They interrupt the normal endocrine function of the brain and pituary gland, and can also potentially affect vision. Ideal management of these tumors is total excision by surgical intervention. If removal is incomplete, follow up treatment with radiation therapy (either standard or radiosurgery) is usually recommended.

Intraventricular ⁹ tumors and cysts

Tumors such as epidermoid tumors, ependymoma, meningioma, and cysts of various types may arise within the ventricular system. Tumors within the ventricles often represent a unique challenge from a neurosurgical standpoint, but can be managed successfully.

Pineal region ¹⁰ tumors

Although uncommon, pineal region tumors also represent a particular challenge from a neurosurgical standpoint due to the location near the center of the brain. Tumors in this area consist of a variety of cell types and occur at all ages.

Pituitary ¹¹tumor

Tumors of the pituitary gland are relatively common in neurosurgical practice. They are divided into two types: functional or non-functional, depending on whether the tumor is secreting excess hormone. Tumors that produce an excess of pituitary hormone are described as functional and the non-secreting tumors are considered non-functional. A tumor can produce a specific hormone, such as human growth hormone, which will produce a disease called acromegaly, in which the bones of the face, hands, and feet enlarge in an adult. It is also associated with enlargement of various organs and can produce a variety of medical conditions. These tumors can be managed successfully with both surgery and radiosurgery, depending on the circumstances. Other hormones produced by these tumors can include prolactin ¹² , thyroid stimulating hormone (TSH) and adrenal stimulating hormone (ACTH). Excess amounts of any of these hormones can cause specific symptoms related to the hormone's basic function.

Differential Diagnosis

Obviously differentiating between these tumors has profound implications for a patient and his/her treatment and is facilitated by recent Neuropathologic advances. At UTMCK, Dr Mahlon Johnson, with Dr. Karla Matteson and the Dept of Medical Genetics, has established the use of fluorescent in situ hybridization to identify genetic abnormalities that have survival or treatment implications in brain tumors. This is now done on tissue from all patients when appropriate. Current analysis includes changes on chromosomes and amplification of a cancer related gene called epidermal growth factor receptor. Identification of abnormalities in these genes has been shown to predict response to various therapies or, in some cases, better predict the length of time a patient may survive without a recurrence. These analyses are now widely used at the major medical school cancer centers in the U.S.

Several reports have shown, for example, that many oligodendrogliomas with specific genetic changes on chromosomes 1p and/or 19q have a better prognosis and respond to specific chemotherapy better than other, similar, malignant brain tumors.

Recent studies suggest that the prognostic value of these analyses may extend to other malignant primary brain tumors as well. For example, glioblastomas, one of the most malignant primary tumors of the brain, has a mean survival time after diagnosis of one year or less. But recent studies indicate that a subset of glioblastomas, those with mutation on chromosomes 1p and 19q, survive twice as long and may show more response to chemotherapy.

- Mahlon Johnson, MD, PhD

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¹ Tumor within the substance of the brain or spinal cord made up of astrocytes – cells which support the nerve cells (neurons) of the brain and spinal cord – often classified from Grade I (slow-growing) to Grade III (rapid-growing).

² A type of cell that surrounds nerve cells and holds them in place. Glial cells also insulate nerve cells from each other.

³ Blood supply

⁴ Oligodendroglioma is a type of glioma and develops from cells called oligodendrocytes that produce the fatty covering of nerve cells. This type of tumor is normally found in the cerebrum, particularly in the frontal or temporal lobes.

⁵ Ependymomas are a rare type of glioma that develop from the cells that line the ventricles (fluid-filled spaces in the brain) and the central canal of the spinal cord. They can be found in any part of the brain or spine, but are most commonly found in the main part of the brain, the cerebrum. Ependymomas may spread from the brain to the spinal cord in the cerebrospinal fluid.

⁶ A brain tumor caused by cancer elsewhere in the body spreading to the brain.

⁷ CyberKnife radiosurgery is a precise, painless, non-invasive radiation treatment that can be an alternative to open surgery in certain cases. Multiple beams of high energy radiation are delivered from multiple points outside of the body and converge precisely at the tumor or lesion inside the body. Each individual beam is not sufficient to cause harm, but the convergence of all the beams at the tumor results in the lesion receiving a very high dose of radiation while sparing nearby normal tissue.

⁸ The three membranes that cover and protect the brain and spinal cord.

⁹ A fluid-filled cavity in the heart or brain.

¹⁰ A type of brain tumor that occurs in or around the pineal gland, a tiny organ near the center of the brain.

¹¹ The main endocrine gland, producing hormones that control other glands and many body functions, especially growth.

¹² Hormone controlling lactation (production of milk)