Condition:
Meningioma
Contents:
What is a meningioma?
Treatment options for meningiomas
When is radiosurgery not the best option for meningiomas?
The results of meningioma radiosurgery
The advantage of CyberKnife radiosurgery for meningiomas
Most common meningioma locations
What tests/studies are needed prior to CyberKnife® radiosurgery for meningiomas?
What can I expect after meningioma CyberKnife radiosurgery?
References
What is a meningioma?
Meningiomas make up approximately 15% of brain tumors. In 97% of cases, the tumor is benign, but in approximately 3% of cases, meningiomas can have malignant features. For the most part, meningiomas are slow growing and, as a consequence, can become quite large before they are detected. Most meningiomas go unnoticed until they cause a neurologic problem, either in the form of headaches or seizures, or in other instances, they can compress normal brain structures and cause a neurologic deficit. In an occasional patient, it is possible to establish that a meningioma has been present for five or ten years before discovery.
Meningiomas are believed to grow from the meningeal layer of membranes that is located between the skull and the brain, hence, the name of the tumor. Thus, even though meningiomas are classified as brain tumors, they are not located within brain tissue, but rather on the surface of the brain. Since the meningeal layer surrounds the entire brain, meningiomas can occur anywhere within the skull (or around the spinal cord, which also is surrounded by meninges). In some instances, meningiomas surround and entrap nerves and blood vessels, making their treatment more difficult. This is often the case for skull base meningiomas, since most of the critical arteries and nerves are located along the base of the skull.
Most meningiomas occur randomly in humans and the origins of this tumor are unknown. However, meningiomas have a familial origin in a small number of patients who suffer from genetic disorders such as neurofibromatosis or multiple meningiomatosis. Meningiomas are much more common in women (with a female to male ratio of 4:1), and older individuals with a peak incidence in the 50 to 70 year range. The female predominance and occurrence later in life has led some to believe that post menopausal changes in female hormones may somehow contribute to the growth of this tumor.
Treatment options for meningiomas
Treatment for meningiomas fall into four broad categories that include:
- Watchful waiting
- Surgical resection
- Conventional radiotherapy
- Stereotactic radiosurgery
Watchful waiting is the process by which a meningioma that has been discovered, is not treated, but rather carefully observed with serial MRI scans performed every 6 to 12 months. This is obviously not an option for patients with large symptomatic tumors. But since meningiomas are most often slow growing, and discovered when small, this is a reasonable option for elderly patients or those with significant medical problems. The main disadvantage of watchful waiting is that treatment of meningiomas becomes more difficult and risky as they increase in size.
Surgical resection has been the standard treatment for meningiomas for more than two generations and has many specific advantages. Most importantly, if the meningioma can be completely resected, and is confirmed to be benign, the cure rate is very high. Furthermore, surgery is uniquely able to provide tissue to a pathologist, who can generally unequivocally confirm the diagnosis of meningioma. The obvious drawbacks to surgical resection are the not inconsequential risks of open surgery, which include bleeding, strokes, neurologic deficits, and infections. The complication rate of surgical resection is highest for meningiomas around the skull base. Furthermore, for many skull base meningiomas, a complete surgical resection is often not possible and the residual tumor is at great risk of re-growing over time.
Conventional radiotherapy - There are basically two types of radiation that are used to treat meningiomas:
- conventional radiotherapy and
- stereotactic radiosurgery.
Conventional radiotherapy is generally used in the treatment of malignant meningiomas, which are often diffuse and hard to localize, or when treating meningiomas that are too large for radiosurgery. For most meningiomas, treatment with conventional radiation is not as aggressive or successful as radiosurgery, and therefore, represents a second line of therapy.
Stereotactic radiosurgery administered with the CyberKnife is one of the most advanced methods for treating meningiomas. During radiosurgery, a highly focused, precisely targeted beam of radiation is used, almost like a surgeon’s scalpel, to deliver a lethal dose of energy to the tumor, while sparing normal brain tissue adjacent to the tumor. The success rate with stereotactic radiosurgery is very high, with approximately 95% of radiosurgically treated meningiomas dying after one or a small series of “staged” treatments. Like any surgical treatment, radiosurgery has risks. These include a small chance that the tumor will continue to grow despite treatment, and a small risk of radiation injury to normal nerves immediately adjacent to the tumor. Overall, these risks are low, typically being substantially less than the microsurgical resection of such a meningioma. This is especially true for skull base lesions.
When is radiosurgery not the best option for meningiomas?
There are several instances where radiosurgery is not the best option for treating meningiomas. For example, large meningiomas are difficult to treat with radiosurgery since the risk of delivering radiation is substantially higher than that for small tumors.
While each case must be evaluated individually, most radiosurgery centers are reluctant to treat meningiomas larger than 3.5 cm in diameter; volume is ultimately a more important factor than any one dimension of the tumor. Furthermore, larger meningiomas often compress the brain and produce symptoms. Surgical resection is uniquely able to promptly decompress the brain and restore neurologic function. Moreover, if there is some suspicion that the tumor being evaluated is not a meningioma, then your surgeon may recommend a biopsy or surgical resection itself so that a definitive diagnosis can be made.
A drawback of radiosurgery is that it destroys the tumor without establishing a pathologic diagnosis. Therefore, a surgeon must be reasonably confident of the diagnosis based on imaging studies alone (MRI or CT), to recommend radiosurgery as a first-line treatment. Obviously, among patients who have had a prior surgical resection and there was either residual meningioma left behind, or the tumor recurred, it is generally not necessary to biopsy a tumor again prior to CyberKnife radiosurgery.
The results of meningioma radiosurgery
Most medical centers report excellent tumor control rates after radiosurgery, on the order of 90 to 95%. The risk of neurologic injury depends on location.
For non-skull base meningiomas, the risk of temporary radiation injury is on the order of 2-3% and the risk of permanent radiation injury on the order of 1%. These complication rates are slightly higher for larger lesions and skull base meningiomas.
If patients have clinical symptoms, such as headaches, double vision, seizures, etc., there is a significant likelihood that these will improve after radiosurgery. However, such improvement typically takes place over many months or even years.
The advantage of CyberKnife radiosurgery for meningiomas
The CyberKnife is a particularly advanced form of radiosurgery. An important advantage for the patient is that no metal frame is screwed into the skull, which enables the operation to be much less painful than other radiosurgical systems.
Although it is non-invasive, the CyberKnife has been proven to be very accurate; it delivers beams of radiation to an accuracy of approximately 1 mm. This measure of precision is at least as good, if not better, than standard frame-based linear accelerators and the Gamma Knife.
Another significant advantage of the CyberKnife frameless approach is that staged (fractionated) treatment is readily possible. In selected cases, there are advantages to administering the radiation over two to five smaller doses, instead of one large dose. This procedure, which is sometimes termed fractionated stereotactic radiosurgery (FSR), makes it possible to more safely treat some larger meningiomas, or those immediately next to critical structures, like the vision (optic) nerve.
Most common meningioma locations
While meningiomas have a wide variety of locations, the following are the most common locations:
1. Cavernous sinus meningioma: These meningiomas are located in a region called the cavernous sinus, and often are wrapped around critical nerves that control eye movement and feeling in the face. Tumors in this location are extremely difficult, if not impossible, to remove with microsurgery because of the appreciable risk of permanent neurological injury. Patients with this type of meningioma often present with double vision, headaches, and numbness in the face.
2. Optic nerve meningioma: These meningiomas occur in and around the optic nerve and, depending on the location of the tumor, usually present with visual loss in one or both eyes. Surgery on these meningiomas is fraught with difficulty, and blindness is a frequent complication of open surgery. Because these tumors are oftentimes inseparable from the optic (vision) nerve, a single radiosurgical treatment also has a very high risk of blindness. Therefore, the typical one-time treatment with a frame-based radiosurgical device cannot be used in such cases. However, with the CyberKnife, we have been able to treat these tumors using a staged treatment with excellent overall results.
3. Tentorial meningioma: This type of meningioma is located along a “meningeal” structure deep in the brain termed the tentorium. If such tumors are located along the medial edge of the tentorium, they can surround important cranial nerves. However, more commonly they involve the lateral tentorial edge, where the tumor can be wrapped around large veins called sinuses. Common presenting symptoms for these tumors include headaches, seizures, and in rare instances, double vision.
4. Cerebellopontine angle (CPA) meningioma: These meningiomas often mimic acoustic neuroma, since both tumor types are located in what is called the cerebellopontine (CPA) angle. Smaller tumors present with either facial numbness or weakness as well as hearing loss. Larger CPA meningiomas compress the brainstem and cerebellum (the balance portion of the brain at the back of the head), resulting in balance problems, dizziness, or frequent falls.
5. Foramen magnum meningioma: These meningiomas occur at the base of the skull where the top of the spinal cord is located. They generally cause their symptoms by compressing the brainstem or upper spinal cord. Primary symptoms include a hoarse voice, swallowing difficulties, balance problems, or weakness and numbness in the arms and legs.
6. Olfactory groove meningioma: These are located at the front of the skull base next to the olfactory (smell) nerves. Primary symptoms include loss of smell or, in rare instances, leakage of spinal fluid from the nose.
7. Sellar meningioma: These tumors are located within an area of the skull known as the sella turcica that is adjacent to the pituitary gland. Primary symptoms of such tumors include headaches, visual loss if there is compression of the optic nerves, hormonal changes if there is compression of the pituitary gland, or motor or sensory deficits if there is compression of the brainstem.
8. Convexity meningioma: Such meningiomas are located along the top of the brain, an area referred to as the convexity of the skull. Primary symptoms can include headaches, seizures, or weakness or numbness in the arms or legs (usually along one side). In most patients, this type of meningioma can be removed through conventional open microsurgery with low risk. However, in elderly patients, or patients with multiple medical problems, it may be preferable to treat meningiomas in this location with radiosurgery.
What tests/studies are needed prior to CyberKnife radiosurgery for meningiomas?
For most meningiomas, an MRI scan is the only study that is needed before various treatment alternatives can be considered. However, certain meningiomas are located in regions which cause symptoms that warrant additional testing. For example, cerebellopontine angle meningiomas can, in some instances, cause hearing loss. For meningiomas in this location, a hearing test, or audiogram, in addition to the head MRI scan, is advisable. Oftentimes, optic nerve meningiomas present with visual loss.
Therefore, when such tumors are suspected, a formal ophthalmologic visual field test is recommended. Sellar meningiomas can cause hormonal changes or be confused with pituitary tumors, so patients with tumors in this location should have serum hormone studies prior to opting for radiosurgery or any other surgery.
Even though meningiomas grow slowly, it is optimal to have an MRI scan within three months of treatment. An up-to-date scan ensures the best possible comparison of tumor size before and after CyberKnife radiosurgery.
What can I expect after meningioma CyberKnife radiosurgery?
Since radiosurgery is an outpatient procedure, the vast majority of patients experience no side-effects. It usually takes six to twelve months after the radiosurgery for the meningioma to begin to die.
Therefore, patients are typically followed postoperatively with serial MRI scans periodically. A common protocol is an MRI scan every six months for the first two years, then once a year for the next two years, and then every two to three years thereafter.
Radiosurgery destroys the tumor cells and turns the tumor into scar tissue. This means that there is typically a visible scar in the MRI scan at the site where the tumor was first located. Such a scar will show up for many years on MRI scans, and is often visually indistinguishable from the original tumor, except for the fact that it gradually shrinks over time. However, not uncommonly, there will be no change in the size of a tumor after radiosurgery, even after several years.
This does not mean that the radiosurgery is not effective, but just that the tumor turned into scar tissue without much shrinkage. In other instances, the tumor can shrink significantly after radiosurgery. It is critical that any meningioma patient who is considering radiosurgery be thoroughly aware of this fact. Radiosurgery is the wrong procedure for any patient that expects the tumor to suddenly vanish on the postoperative MRI scan.
Most patients feel great and are without any symptoms after radiosurgery. In rare instances, a patient can experience mild headaches or dizziness during the first 24 hours after treatment. Other side-effects are quite rare.
References
- Chang SD, Main W, Martin DP, Gibbs IC, Heilbrun MP: An analysis of the CyberKnife: a robotic frameless stereotactic radiosurgical system. Neurosurgery. 2003 Jan: 52(1):140-7.
- Maciunas RJ, Galloway RL Jr, Latimer JW: The application accuracy of stereotactic frames. Neurosurgery. 1994 Oct: 35(4):682-94.
- Chang SD, Adler JR Jr, Martin DP: LINAC radiosurgery for cavernous sinus meningiomas. Stereotactic and Functional Neurosurgery. 1998: 71(1):43-50.