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Treatment Options
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There are three treatment options available to a patient. These options are:
- Observation
- Microsurgical Tumor Removal
- Radiation ("radiosurgery" or "radiotherapy")
Choosing the best option is a decision that must be made by the patient and physician after careful review of the patient's age, physical health, tumor size and location. The skill and experience of the treating physician are also factors to be considered, and an open discussion should occur.
- Observation - Watch and Wait:
Acoustic neuromas may be discovered incidentally in the course of evaluating another problem, or when the tumor is very small and there are few symptoms. Since acoustic neuromas are benign tumors and produce symptoms by pressure on surrounding nerves, careful observation over a period of time may be
appropriate for some patients. When a small tumor is discovered in an older patient, observation to determine the growth rate of the tumor may be indicated if serious symptoms are not present. If it appears that the tumor will not need to be treated during the patient's normal life expectancy, treatment and its potential complications may be avoided. In this case, MRI's are performed periodically, and if the tumor does not show significant growth, observation is continued. On the other hand, if the tumor shows progressive increase in size, treatment may become necessary.
Another group of patients for whom observation is indicated includes
patients with a tumor in their only hearing or better hearing ear, particularly
when the tumor is of a size that hearing preservation with removal would
be unlikely. In this group of patients, MRI is used to follow the
growth pattern. Treatment is recommended if either the hearing is
lost or the tumor size becomes life threatening, thus allowing the patient
to retain hearing for as long as possible.
- Microsurgical Tumor Removal:
- Partial Tumor Removal:
Partial removal of an acoustic neuroma may be indicated in some patients in order to reduce the risk of complications, with the realization that further surgery may be needed in the future. Older patients with large tumors causing a threat to life may elect to have their surgeon sub-totally remove their tumor. Partial tumor removal has also been advocated in some patients who have large tumors in their only hearing ear. This surgical management will reduce the tumor in size, so that it may cause no threat to the patient's health during his or her life expectancy. This approach may greatly reduce the probability of any facial nerve dysfunction as a result of the surgery, but there is still a risk for hearing loss with partial removal. Periodic MRI studies are important to follow the potential growth rate of residual tumor.
- Total Tumor Removal:
Many tumors can be entirely removed by surgery. Microsurgical technique and instruments, along with the operating microscope, have reduced the surgical risks of total tumor removal. Preservation of the facial nerve is the primary task for the experienced acoustic neuroma surgeon
to prevent permanent facial paralysis. Preservation of hearing in the affected ear is also an important goal in patients who present with functional hearing.
Facial nerve function is electrically monitored during surgery. This is a valuable aid for the surgeon while the tumor is being removed from the facial nerve during surgery. Cochlear nerve electrical monitoring is also employed during operations when preservation of hearing is a goal.
- Surgical Procedures
At the last NIH Consensus Conference (1991) the best published surgical outcomes in the treatment of acoustic neuroma are related to the surgical approaches of translabyrinthine, retrosigmoid/sub-occipital and middle fossa. The approach is based on several factors such as tumor size, location, skill and experience of the surgeon, and whether or not hearing preservation is a goal. The surgeon and the patient should thoroughly discuss the reasons for a selected approach. Each of the surgical approaches has advantages and disadvantages, and excellent results have been achieved using any of the approaches.
Translabyrinthine Approach:
The translabyrinthine approach may be preferred by the surgical team when the patient has no useful hearing, or when an attempt to preserve hearing would be impractical. The incision for this approach is located behind the ear. It involves removing the mastoid bone and some bone in the inner ear, allowing excellent exposure of the internal auditory canal and tumor site. This approach facilitates the identification of the facial nerve in the temporal bone prior to any removal of the tumor. The surgeon, therefore, has the advantage of knowing the location of the facial nerve prior to tumor dissection and
removal. A secondary incision is needed to harvest fat from the abdomen. This is typically just above the groin area and below the belt line. Fat is the substance that is used to prevent a cerebral spinal fluid leak. The leak rates have been consistently falling in prominent U.S. centers.
Retrosigmoid/Sub-occipital Approach:
This approach creates an opening in the cranium behind the mastoid part of the ear. The surgeon observes the tumor from its posterior surface, thereby seeing the tumor in relation to the brainstem. When removing large tumors through this approach, the facial nerve can be exposed by early opening of the internal auditory canal. Small tumors can be removed with hope of preserving hearing in some patients through this approach.
Middle Fossa Approach:
This approach is utilized primarily for the purpose of preservation of hearing. A small window of bone is removed above the ear canal to allow exposure of the tumor from the upper surface of the internal auditory canal beyond the inner ear.
- Radiation:
The third treatment option for an acoustic neuroma is radiation. Stereotactic radiation therapy, referred to as "radiosurgery" (typically performed in a single session) or "radiotherapy" (typically delivered over an extended period of time in multiple doses of radiation) is a technique based on the principle that radiation delivered precisely to the tumor will arrest its growth while minimizing injury to surrounding nerves and brain tissue. This non-invasive procedure can be performed in a one-dose treatment on an outpatient basis, or in a multi-dose treatment ranging from several days to over several weeks.
In single dose treatments, many hundreds of small beams of radiation are aimed at the acoustic neuroma. This results in a high dose of radiation to the tumor and very little to any surrounding brain structures. Radiosurgery is delivered as a one-time, outpatient treatment. Many patients have been treated this way with high success rates. Facial weakness or numbness, in the hands of experienced radiosurgeons, occurs in only a small percent of cases and is usually temporary. Hearing can be preserved in many cases.
The multi-dose treatment, fractionated stereotactic radiosurgery (FSR), delivers smaller doses of radiation over a period of time, requiring the patient to return to the treatment location on a daily basis, sometimes over several weeks. Each visit only takes a few minutes and most patients are free to go about their daily business before and after each treatment session. FSR may become a more effective treatment as greater experience is gained with this technique.
The treatment team may consist of a neurosurgeon, a neurotologist, a radiation oncologist and a physicist. While in the past, conflicting reports occurred among physicians, radiosurgery has an increasing role in the management of patients with acoustic neuromas. Patients must understand that this treatment does not remove the tumor as in microsurgery, but in some cases shrinkage does occur. Further, the patient must understand that close follow up for a lifetime with MRI scanning is needed to track the results of radiosurgery. It appears that more favorable cases are those patients with small to medium size tumors, without brainstem indentation. Indeed, side effects can occur when the brainstem is irradiated, and in some cases of large tumors; radiation is contraindicated. Patients should understand there have been sporadic reports of malignant degeneration after radiotherapy, but the incidence of this happening appears to be rare.
There can be confusion regarding which type of radiation device to select. The greatest number of peer reviewed articles have come from centers with Gamma Knife. Typically multiple shots of radiation are configured to create a three dimensional volume of radiation that confirms to the tumor precisely. The source for the radiation is cobalt 60 and typically that dose is 11 to 14 Gy, depending on hearing status and the patient's condition. The patient wears a stereotactic frame that provides accuracy and precision. The radiation is usually administered once over 30-50 minutes depending on the specific tumor.
Linear accelerator radiosurgery (LINAC) uses a conventional radiotherapy machine to deliver radiation to the target. Patients are placed in a stereotactic head frame to allow precise treatment. Multiple isocenter techniques (the precise mathematical location where a radiation dose is aimed) are used to develop a conformal plan.
Fractionated techniques have their advocates as well. The rationale for this technique may be an attempt to preserve hearing and there is research now that reinforces this. At this time, more long term studies are needed in all types of radiosurgery. Problems come with lack of follow up or standard protocol reporting of results.
Just like microsurgery, patients are advised to inquire about a particular center's experience with acoustic tumors. The longer the center has been active, published, and greater number of patients treated is an appropriate way to judge the potential outcome. No center can guarantee the outcome despite statements of the "latest and greatest technology".
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