A tumor is an abnormal mass of tissue that grows on or inside the body. It is known as primary if located where its growth first started, or secondary if it began growing elsewhere in the body and metastasized, or spread, to its present location. Most primary brain tumors do not metastasize outside the brain.
Inside the skull, tumors can grow almost anywhere: within brain tissue, from the meninges, or inside the ventricular system. They can be encapsulated (self-contained) or interwoven with blood vessels, nerves, or other brain structures from which they cannot be removed without devastating consequences. Metastatic tumors are usually well localized, may occur alone or in clusters, and may spread throughout much of the brain.
A benign tumor usually is encapsulated, does not spread to other areas of the body, grows slowly, and often causes problems by compressing brain tissue. A malignant tumor grows uncontrollably, spreads throughout the brain, and destroys brain tissue.
A brain tumor may at first cause the vague feeling of being “unwell”. This may be followed by other, more specific symptoms: dull, persistent headache; nausea or vomiting; generalized weakness; vision problems. Because the left side of the brain governs the right side of the body, and vice versa, a tumor will cause specific weakness or loss of movement on the opposite side of the body. Some symptoms may be caused by the increased pressure inside the skull from brain swelling, which can temporarily be treated with a steroid medication.
Because brain tissue is irritated by the tumor, the brain can temporarily “short-circuit” as its normal electrical activity is interrupted. These periods of uncontrolled brain activity can cause seizures, which may be generalized and cause contractions of all parts of the body, loss of consciousness or bladder and bowel function. The seizures may instead be of a focal nature, affecting only one arm, a leg, or part of the face. Seizures usually can be controlled with anticonvulsant medications.
A detailed history-taking of the patient’s symptoms and a physical examination are done first, followed by any of several tests, such as x-ray studies, Computerized Tomography (CT) scans, Magnetic Resonance Imaging (MRI), and angiograms. All findings are used to evaluate the patient’s symptoms, determine the tumor’s exact location, and provide the physician with a tentative diagnosis of the tumor type.
During surgery, ultrasound imaging may be used to pinpoint the tumor’s precise location and help the surgeon plan his approach for its removal.
If an emergency craniotomy is required, an extensive workup may not be possible.
Primary brain tumors include those arising from the various cell types within the brain tissue:
- Astrocytomas are tumors that arise from the glial cells and are typically classified as grade 1 through grade 4 dependent on their rate of growth and vascularity as well as other factors.
- Oligodendrogliomae are tumors that arise from the oligodendrocytes in the brain and typically are slow growing tumors and will have a more favorable outcome.
- Ependymomas 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 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 gamma knife radiosurgery.
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.
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.
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, 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.
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 8th 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 3rd ventricle and can grow to a very large size before discovered. They interrupt the normal endocrine function of the brain and pituitary 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.