Cranial Anatomy - Brain Tumors

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Articles and graphics courtesy of Medtronic Sofamor Danek, 2002.

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Cranial Anatomy
Brain Tumors

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.

What symptoms can it cause?
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.

How is it evaluated?
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.

Meningioma
Growing from abnormal cells of the meninges, meningioma is a slow-growing tumor that shares the dura's rich blood supply. It is very often attached to dura and so may be immediately visible when the dura is opened.

It is usually a benign tumor and well encapsulated, but removal may be complicated by its size, firmness, and attachment to vital blood vessels or brain tissues.

A large meningioma or one that is difficult to remove may require a long, tedious surgery and can cause further brain swelling and blood loss.

Often the dura removed during tumor surgery may be replaced with other body tissue (fascia) or a dura substitute.

Glioma
Glial cells support the brain's functioning nerve network and are the site of tumors inside the brain. Gliomas are "graded" according to their degree of malignancy.

Often when the dura is opened, the brain is swollen but otherwise may appear normal.

The "center" of the glioma may readily be identified, but because the tumor gradually spreads into surrounding tissue the boundaries of a glioma are harder to identify.

It may take months for the cells around the edges of the tumor to appear abnormal, yet they can be affected long before they "show" themselves. This is why glioma usually cannot be removed completely, as even one remaining cell can continue the tumor's growth.

Metastatic tumor
Often lying close to the brain's surface, where it irritates the normal tissue around it, a metastatic tumor is one that began in another body organ and traveled in the bloodstream to the brain.

Grown from a "seed" of non-brain tissue (from the breast, kidney, or lung, for example) a metastatic tumor often can be separated from the surrounding brain more easily. It only a single lesion exists, all or part of it usually can be surgically removed.

Articles and graphics courtesy of Medtronic Sofamor Danek, 2002.

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