Although stereotactic radiation provides a noninvasive approach to treating acoustic neuromas, it also carries the risk of hearing loss over time for a sizable portion of patients, according to experts.
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May 2008Risk of Hearing Loss
The true long-term incidence of hearing loss associated with stereotactic radiation is not known but occurs in a significant number of patients, said Douglas C. Bigelow, MD, Associate Professor in the Department of Otorhinolaryngology-Head and Neck Surgery, Co-Director of the Center for Cranial Base Surgery, and Director of the Division of Otology/Neurotology at the University of Pennsylvania in Philadelphia.
New research presented at the 2008 Triological Society Southern Section meeting in January concluded that patients with acoustic neuromas treated with stereotactic radiation have a significant decrease in auditory function over time.
Researchers at the University of Kentucky evaluated 17 patients selected from an acoustic neuroma stereotactic radiation registry of 113 individuals treated from 1991 to 2005. Patients were followed for a mean of 2.8 years.
Overall, 58% of patients with useful hearing pretreatment experienced hearing loss post-treatment, explained one of the study authors, Byron Young, MD, Professor and Chair of Neurosurgery and Director of Kentucky Neuroscience Institute.
Although short-term hearing preservation rates associated with stereotactic radiation tend to be good, the true measure of an intervention is its long-term results, commented Daniel Coelho, MD, Fellow in the Department of Otolaryngology at New York University School of Medicine.
Our experience has been that many patients undergoing radiation therapy have significant decreases in their speech perception as they approach and pass five years post-treatment, he said.
Rates of hearing loss tend to grow as patients are followed, agreed Dr. Bigelow. For example, in a University of Pittsburgh study of 121 hearing patients who underwent stereotactic radiation, the serviceable hearing rate was 74% at more than three years follow-up (Int J Radiation Oncol Biol Physics 2007;68(3):845-51).
Surgery also has a high risk of hearing loss, depending on the size of the tumor, with smaller tumors posing less risk. Patients and physicians should remember that significant risk of hearing loss exists with any treatment for acoustic neuroma.-Douglas C. Bigelow, MD
Why Hearing Loss May Occur
Gradual hearing loss may occur with stereotactic radiation because in addition to causing tissue scarring that cuts off blood supply to the tumor and inhibiting its growth, the treatment can also block blood supply to the inner ear affecting auditory nerves and function, said John W. House, MD, President of the House Ear Institute in Los Angeles.
The tumor itself, which generally stops growing but is not removed, may also contribute to hearing loss, said Dr. Bigelow. Even patients who have chosen to undergo observation rather than radiation will often experience hearing loss over time, even if the tumor does not grow, he said. The longer you watch with acoustic neuroma, the greater the chances that hearing will get worse, explained Dr. Bigelow.
Factors Affecting Risk
The risk of hearing loss following stereotactic radiation depends partly on the radiation dose, said Dr. Young. We now use 12.5 Gy, he said.
Additionally, the better the patient’s hearing is prior to treatment, the better chance it will be preserved after radiosurgery, said Dr. Young.
The size of the tumor also plays a role in the risk of losing hearing, noted Dr. Bigelow. With radiation the best results occur with small tumors, he said.
Definition of ‘Loss’ Important
Risk of hearing deficits also depends on the definition of loss, said Dr. Coelho. For example, a drop of 1 decibel on pure tone average may result in a reclassification of hearing, depending on what scale is being used. Despite this drop, patients may continue to have serviceable hearing, he explained.
Likewise, preservation of hearing is a meaningless term if the pretreatment speech perception was poor, added Dr. Coelho. If there is no serviceable hearing to preserve, then losing it is not a risk. Critically analyzing the data and methodology used in reporting results is important.
He and his colleagues recently concluded that patients with acoustic neuromas less than 1.5 cm and no serviceable hearing, defined as word recognition score (WRS) of less than 50%, should receive surgical resection as the primary treatment if able to tolerate it, rather than stereotactic radiation. Their study of 57 patients, presented at the 2008 Triological Society Eastern Section meeting in January, found that surgery offered significantly better rates of disequilibrium and quality of life with respect to the patient’s disequilibrium.
General Contraindications
A number of factors might prohibit a clinician from recommending stereotactic radiation, noted Dr. Coelho. For example, a tumor larger than 3 cm can result in clinically significant postradiation acute edema, he said.
Dr. House generally does not use stereotactic radiation on patients with tumors larger than 2.5 cm, and in those with cystic tumors or with vestibular symptoms.
In addition, patients with disabling vertigo or imbalance generally do poorly following stereotactic radiation, said Dr. Coelho.
Age also influences whether a patient is a candidate for stereotactic radiation, said Dr. Coelho. This procedure offers an excellent alternative for elderly patients unable to tolerate surgery, he explained. However, younger patients may not want to pursue the stereotactic procedure because of the long-term potential of recurrence or developing radiation-induced malignancy.
We generally refer our young patients healthy patients to surgery because we don’t know the long-term effects of radiation, noted Dr. House. However, the procedure is indicated in older patients who have a documented growing tumor, he said.
Pre- and Post-Treatment
If stereotactic radiation is chosen, the physician needs to map the tumor with an MRI to determine treatment boundaries and the radiation dose, said Dr. House.
Patients should also receive an MRI six months after treatment to ensure that the tumor is not growing, said Dr. Bigelow. The tumor may initially show some swelling on this scan, so another MRI should be scheduled for six months later. Dr. Bigelow then sees patients once a year for an MRI and audiograms to monitor hearing.
Some tumors will start to grow again after five to 10 years, so ongoing follow-up is important, said Dr. House.
What Patients Should Know
Physicians need to provide complete disclosure of treatment options and their risks and benefits, said Dr. Coelho. Open and frequent dialogue between doctor and patient cannot be stressed enough, he said.
For example, patients should know that radiation does not cure acoustic neuromas but may prevent growth in about 80% of the tumors, said Dr. House. In contrast, at his facility, microsurgery has close to a 100% cure rate.
Some published data show higher control rates for stereotactic radiation. For example, in tumors no larger than 3 cm, control rates were 98% in a University of Pittsburgh study (N Eng J Med 1998;339:1426-33), noted Dr. Young.
When contemplating surgery, patients should remember that surgery carries the risk of infection, hemorrhage, and stroke if a blood vessel is injured, added Dr. Young. Moreover, with surgery, patients will spend three to five days in the hospital and three or four weeks recovering at home.
Surgery also has a high risk of hearing loss, depending on the size of the tumor, with smaller tumors posing less risk, said Dr. Bigelow. Patients and physicians should remember that significant risk of hearing loss exists with any treatment for acoustic neuroma.
If patients lose their hearing with surgery, this usually occurs on the day of the procedure, added Dr. Young.
Dr. House and his colleagues report a 70% hearing preservation rate in patients undergoing surgical removal of tumors less than 1.5 cm through the middle fossa.
Infection associated with surgical removal of acoustic neuroma occurs in two of every 600 patients, he added.
In contrast, stereotactic radiation does not have an infection risk, and patients can receive the treatment on an outpatient basis and return to work within a day or two, said Dr. Young.
In addition to hearing loss, recurrence, and radiation-induced malignancies, however, fairly rare short- and long-term complications of stereotactic radiation include change in balance, chronic vertigo, cerebellar or cerebral edema, facial nerve weakness, hydrocephalus, trigeminal neuralgia, and facial nerve weakness, said Dr. Coelho.
Patients should also understand that stereotactic radiation will not remove the tumor, said Dr. House. Rather, it is designed to prevent the tumor from growing.
Some patients psychologically don’t do well having a tumor in their head, and for them, surgery may be the best option, said Dr. Bigelow.
Patients also need to be aware that observation is another option for addressing acoustic neuromas, said Dr. Coelho. Data show that in the long run most patients with acoustic neuromas who opt for observation will have worse outcomes than treated matched controls, he said. However, on an individual basis, this may be the most appropriate approach, especially for small, intracanalicular tumors.
Dr. Young usually observes patients if the tumors are small and hearing is normal or near normal, and an MRI has shown that the tumor is not growing.
The Bottom Line
Overall, physicians should keep in mind that stereotactic radiosurgery continues to evolve, said Dr. Coelho. Like any modality, it has advantages and disadvantages that must be considered and discussed with the patient, he said. It remains the neurotologist’s responsibility to lead that discussion.
©2008 The Triological Society