July 23, 2022
Vestibular schwannomas — the preferred term for acoustic neuromas — are heterogeneous benign tumors that can negatively impact quality of life. Optimal management requires expertise with evolving treatment options.
"We're now prioritizing functional outcomes over a definitive cure," says Michael J. Link, M.D., a neurosurgeon at Mayo Clinic in Rochester, Minnesota. "There are multiple reasonable treatment options, and patient preference plays a major role in shared decision-making."
Although rare, vestibular schwannomas are more common than previously known, with an approximate prevalence of 1 in 2,000 people. In a review published in the April 8, 2021, edition of The New England Journal of Medicine, Mayo Clinic researchers noted that the increasing prevalence is probably due to greater access to enhanced diagnostics rather than an actual biological shift. Diagnosis often occurs when tumors are very small and patients are above age 70 and have minimal symptoms.
But the tumors' unpredictable clinical behavior complicates decision-making. Mayo Clinic has neuroradiologists, neurologists, neurosurgeons and otolaryngologists with deep experience in caring for individuals with vestibular schwannomas.
"Depending on the individual patient and tumor, the strategies include a wait-and-scan approach, irradiation, microsurgery, or a combination of these methods," Dr. Link says. "Each strategy has advantages and limitations. Data show that quality of life is affected more by the diagnosis itself and patient-related factors than by the actual treatment choice."
Advanced imaging and treatment
Sporadic, unilateral tumors account for more than 95% of vestibular schwannomas. Less commonly, multiple tumors develop in individuals with certain genetic disorders such as neurofibromatosis type 2. Mayo Clinic's Neurofibromatosis Type 2 Clinic provides expert, multidisciplinary care for teenagers and adults with this tumor-predisposing genetic disorder.
Vestibular schwannomas can cause varying levels of hearing loss, tinnitus and dizziness. The association between tumor size and the severity of symptoms is limited, and symptom progression isn't strongly correlated with tumor growth.
"Lifelong follow-up is recommended due to the tumor's capacity for saltatory or delayed growth," Dr. Link says. "Worsening symptoms aren't reliable barometers for tumor growth."
Mayo Clinic uses volumetric measurements of tumors — obtained by segmenting and analyzing patients' MRIs in a 3D laboratory — to assess tumor growth.
"Volumetric analysis can detect what might not be readily evident by visual examination of the MRI," says John (Jack) I. Lane, M.D., a neuroradiologist at Mayo Clinic's campus in Minnesota.
Unlike most tumors, which are generally spherical or elliptical, vestibular schwannomas have highly irregular shapes. "As a result, a 2- or 3-millimeter change on a linear scan can result in a 50% to 80% change in total tumor size, which would be an indication that treatment is needed," Dr. Link says.
Mayo Clinic specialists also evaluate overlays of a patient's current and previous scans. "We can drop the previous image right on top of the current image, and then use a slide bar to pan between them," Dr. Lane says. "Often that analysis can be even more sensitive than volumetric changes in assessing tumor growth."
These detailed evaluations help guide treatment recommendations. A wait-and-scan approach is generally suggested for tumors with a maximum diameter in the cerebellopontine angle of less than 1.5 cm.
"Hearing loss is likely to progress with this approach, even if the tumor doesn't grow," Dr. Link says.
If tumor growth is confirmed, Mayo Clinic generally recommends radiosurgery or microsurgery. Radiosurgery is reserved for tumors measuring less than 2.5 cm. The options include Gamma Knife radiosurgery — which Mayo Clinic has performed for more than 30 years — as well as intensity-modulated therapy and proton therapy.
"Radiosurgery doesn't cure the tumor. The goal is to prevent tumor growth," Dr. Link says. "Between 50% and 70% of patients retain serviceable hearing in the treated ear."
Microsurgery is the treatment of choice for large tumors associated with complications such as brainstem compression, hydrocephalus, trigeminal neuralgia or neuropathy. The procedure is performed with an operating microscope and intraoperative neural monitoring.
"The goal is maximal tumor removal with preservation of neurological function," Dr. Link says.
Among individuals with small tumors, 40% to 70% retain serviceable hearing after microsurgery. For tumors larger than 2.5 cm, the probability of preserving serviceable hearing after surgery is less than 5%. Total resection of large tumors also risks permanent partial or complete facial nerve paralysis.
To minimize those complications, a tumor remnant might be left around the facial nerve and brainstem. About 30% of tumors regrow to some degree after subtotal tumor resection. As described in a study published in the August 2021 issue of Acta Neurochirurgica, Mayo Clinic usually treats residual tumors with adjuvant radiosurgery.
For more information
Carlson ML, et al. Vestibular schwannomas. The New England Journal of Medicine. 2021;384:1335.
Neurofibromatosis Type 2 Clinic. Mayo Clinic.
Kiyofuji S, et al. Large and small vestibular schwannomas: Same, yet different tumors. Acta Neurochirurgica. 2021;163:2199.
Refer a patient to Mayo Clinic.