Treatment options for skull base tumors

Jun 28 2005

It is estimated that in 2000, more than 359,000 persons were living with a diagnosis of a primary brain tumor in the United States. In 2005, it is estimated that nearly 12,800 deaths will be associated with malignant tumors of the brain and other parts of the central nervous system. Brain tumors are the leading cause of cancer-related deaths in children age 19 and younger.

A brain tumor is an abnormal mass of tissue in which cells grow and multiply uncontrollably, seemingly unchecked by the mechanisms that control normal cells. Tumors of the skull base usually cause few symptoms until they have grown large enough to affect neurological function. Symptoms may include double vision, facial pain or twitching, hearing loss, loss of balance or dizziness, hoarseness, and tongue weakness. Both benign and malignant tumors occur along the cranial base. Diagnosis is made primarily through computed tomography (CT or CAT scan) and magnetic resonance imaging (MRI). In some cases, cerebral angiography is utilized.

According to the American Association of Neurological Surgeons (AANS), tumors that were once considered to be inoperable can now be accessed and removed -- sometimes completely -- and often without impaired neurological function. Over the last 20 years, new and sophisticated techniques have led to advances in the treatment of skull base tumors that were previously considered inoperable.

The skull base, or bottom of the skull, is complex because many nerves that carry signals to and from the brain cross this area. Many skull base tumors are accessed through a craniotomy, a procedure in which a neurosurgeon makes a temporary opening in the cranium, or skull, as close as possible to the tumor site. The basic idea of skull base surgery is to approach the tumor from underneath or from the side by removing specific parts of the bone of the skull base. Thus, the tumor can be exposed with little or no brain retraction.

Computer-assisted tumor removal is a surgical method that uses computer-generated models of the tumor generated by data obtained from state-of-the-art computer imaging techniques. This allows neurosurgeons to plan and simulate the surgical procedure prior to operating, with the goal of reaching the brain tumor using the safest and least invasive method possible. Possible advantages of this surgery include use of smaller incisions, less injury to normal brain tissue, the ability to remove more complex tumors, and less blood loss and pain than in similar traditional surgery.

A newer, minimally invasive approach allows neurosurgeons to utilize a tiny endoscope with a camera on the end, which is inserted through the nostril, eyebrow, or other area of the face into the skull base. The camera provides surgeons with a panoramic view and in some cases allows them to remove the tumor completely. Endoscopic brain surgery can only be utilized in certain cases and may be particularly beneficial in treating particular types of benign tumors.

Radiosurgery is a treatment method that uses computerized calculations to focus radiation at the site of the tumor while minimizing the radiation dose to the surrounding brain. Radiosurgery may be an adjunct to other treatments, or it may represent the primary treatment technique for some tumors.

Tumors that can occur at the skull base include meningiomas, chordomas, schwannomas, glomus jugulare tumors, craniopharyngiomas, and pituitary adenomas.

Meningiomas are tumors that originate from the meninges, the membrane-like structures that surround the brain and spinal cord. The majority of these are benign, but some can be malignant.

Chordomas are benign, slowly growing tumors that are most prevalent in people age 50 to 60. Their most common locations are the base of the skull and the lower portion of the spine. Although these tumors are benign, they may invade the adjacent bone and put pressure on nearby neural tissue. These are rare tumors, contributing to only 0.2 percent of all primary brain tumors.

The most common type of schwannoma, acoustic neuromas, are benign tumors of the eighth cranial nerve, or vestibular-cochlear nerve, which travels from the brain to the ear. Although these tumors are noncancerous, they can cause serious complications and even death if they grow and exert pressure on nerves and eventually on the brain.

Skull base glomus jugulare tumors are rarely malignant and are typically located just under the skull base, at the top of the jugular vein. Glomus jugulare tumors are the most common form of glomus tumor. However, glomus tumors in general contribute to only 0.6 percent of neoplasms of the head and neck.

A craniopharyngioma is a benign tumor that develops near the pituitary gland. Craniopharyngiomas may cause symptoms by increasing pressure on the brain, disrupting the function of the pituitary gland, and damaging the optic pathways.

Pituitary adenomas, which are benign, are the most common tumors in the pituitary gland. Endoscopic techniques may be beneficial in treating this type of tumor. A tiny endoscope inserted through the nostril is placed in front of the tumor in the sphenoid sinus, and the tumor is removed with specially designed surgical tools. Postoperative discomfort is usually minimal.