The following neurological diseases can be treated by Gamma Knife® Radiosurgery:
- Pituitary Tumors
- Acoustic Neuromas
- Metastatic Brain Tumors
- Trigeminal Neuralgia
- AV Malformations
The pituitary is a small, pea-sized gland that hangs from the hypothalamus, a structure at the base of the brain, by a thread-like stalk that contains both blood vessels and nerves. It controls a system of hormones in the body that regulate growth, metabolism, the stress response, and functions of the sex organs via the thyroid gland, adrenal gland, ovaries, and testes.
A pituitary tumor is an abnormal growth of cells within the pituitary gland. Most pituitary tumors are benign, which means they are non-cancerous, grow slowly and do not spread to other parts of the body, however they can make the pituitary gland produce too many hormones, which can cause problems in the body. Tumors that make hormones are called functioning tumors, and they can cause a wide array of symptoms depending upon the hormone affected. Tumors that don’t make hormones are called non-functioning tumors.
Benign tumors of the vestibular nerve (vestibular schwannomas or acoustic neuromas) begin within the base of the skull and slowly expand into the skull cavity. Slow and progressive destruction of hearing in the affected ear, a sense of imbalance, weakness of facial movement, and facial numbness occurs progressively in most patients. Interestingly, there is minimal or no growth in some individuals. Thousands of patients with acoustic neuromas have been treated over the past 25 years by means of the Gamma Knife and the results compare favorably with the published results of microsurgery. Reports of re-operation on individuals treated by Gamma Knife being more difficult or dangerous are unsubstantiated. Re-operation is quite rare and failure of control may be retreated by radiosurgery. There are no reports of cancer being caused by radiosurgery.
Accounting for 20% of all brain tumors and about 25% of all primary spinal cord tumors, the most common are called “meningiomas”. There are three layers of protective tissue (called the meninges) that cover the brain; the thick dura mater (outer layer), the arachnoid (middle), and the pia mater (innermost to the brain). Meningiomas begin in the dura.
They are more common in women than in men. While meningiomas affect people of all ages, they are most common among people in their 40s. Meningiomas usually grow slowly, generally do not invade surrounding normal tissue, and rarely spread to other parts of the CNS or body.
Metastatic disease can be viewed as two simultaneously occurring diseases. Brain cancer and systemic cancer (elsewhere in the body). Each disease has quite different mortality rates. Untreated brain metastases are rapidly fatal, while systemic cancer may not be.
Metastatic brain disease is a focal disease and focal control of the tumor is paramount to patient survival. The approach in the past has been to treat metastatic brain disease as a whole brain disease, with whole brain radiation (WBR). Because of poor local control of tumor growth when treated solely by WBR, brain metastases in the past were rapidly lethal. Therefore patients with brain metastases did not benefit from many advances in cancer therapy (immunotherapy, chemotherapy, conformal radiotherapy etc.) because these therapies don’t effectively reach brain metastases and individuals died quickly from neurological progression.
There are basically two types of brain tumors. Primary brain tumors arise from the cell tissues, which make up the brain, its blood vessels and the tissues which surround the brain within the skull. On the other hand, secondary brain tumors arise outside the skull and travel through the blood stream to lodge and grow within the brain. Unfortunately these metastatic brain tumors are usually malignant. They grow and kill rapidly unless treated. Common sites of origin for metastatic tumors are cancers of the breast, lung, and skin (melanoma).
The most common primary brain tumors arise from brain tissue itself. Glial cells are the supporting cells of the brain, which provide a structural framework to contain and nourish brain neurons. For unknown reasons these cells undergo a change, which results in slow or rapid growth by cell replication.
There exists no published randomized trial comparing standard treatment of glioblastomas and anaplastic astrocytomas with standard treatment and radiosurgery. A recent study of patients treated with a Gamma Knife boost following surgery or biopsy, and patients treated at recurrence of disease, roughly 6 months after initial treatment showed improved survival benefit from GK radiosurgery. Survival after treatment with first recurrence of GBM was somewhat better (30 months) than initial boost treatment (20 months). About 1 in 5 patients with GBM required reoperation after GK radiosurgery, mostly for tumor recurrence rather than tumor necrosis. The 2-year survival rate for GBM was 51%. Individuals with anaplastic astrocytoma faired better with a median survival of 32 months and 2 year survival of 67%. The tumors treated with radiosurgery were small, 6 cm 3. (Kondziolka D, et al .J Neurosurg. 1997;41:776-785).
Trigeminal neuralgia is a facial pain syndrome consisting of sharp, lancinating pain in the face. The pain is often described as shock-like stabs of pain. The pain is only on one side of the face and may be elicited by touching trigger points in the skin or gums. There is no associated numbness (unless there is co-existing multiple sclerosis). Often there may be spontaneous remissions from pain lasting weeks to years. Interestingly, this pain usually responds to carbamazepine (Tegretol), an oral anticonvulsant medication.
Trigeminal neuralgia is usually caused by compression of the sensory (trigeminal) nerve within the skull by a small artery or vein at the point where the nerve joins the brain stem. Sometimes a small, benign tumor compressed the nerve, causing jolts of electrical shock-like pain to radiate into the face. A few percent of tic patients suffer from multiple sclerosis. In this case the inflammatory response affecting the brain also involves the trigeminal nerve, causing paroxysmal pain.
Tic douloureaux is unique among pain disorders because nearly all treatments work for a period of time. Over the years peripheral nerve avulsion, heating, cooling, compressing, decompressing, chemical ablation, and irradiation have all enjoyed varying degrees of success. Because of the effectiveness of carbamazepine (Tegretol), its use is usually the first level of treatment. Other anticonvulsants may be tried, but these are not usually as effective. When oral medication fails to control this dreadful pain, other surgical measures are quite effective.
Arteriovenous malformations (AVM’s) are an unusual collections of arteries and veins which are congenital in origin and occur throughout the body. When they occur within the brain they cause symptoms in various ways. Most importantly. they can spontaneously bleed resulting in a stroke with lasting neurological problems or even death. Additional symptoms include a seizure, progressing neurological deficits, and headaches.
AVM’s have several forms, such as a direct connection between an artery and vein, an AV fistula. Unusual collections of veins which bleed and cause seizures are cavernous angiomas. Abnormalities of very small vessels are capillary angiomas. The most important (and dangerous) are AVM’s which have both arterial and venous components. These AVM’s have a 3 to 4% chance of spontaneous hemorrhage each year. Roughly 10% of the hemorrhages will be fatal and about 15% of victims will suffer a continuing neurological deficit, such as weakness, sensory or visual loss, speech abnormality, etc.