An acoustic neuroma, also known as a vestibular schwannoma, is a noncancerous tumor that develops on the eighth cranial nerve, which connects the inner ear to the brain. This nerve transmits both sound and balance information, which is why the tumor’s growth often leads to hearing loss, ringing in the ear (tinnitus), and issues with balance. The management of this condition is highly individualized, and there is no single “best” treatment that applies to every patient. Medical professionals choose from a set of effective options that fall into three broad categories: observation, surgical removal, or focused radiation therapy.
Active Surveillance for Small Tumors
Active surveillance, often described as “watchful waiting,” is a common initial approach, particularly for small tumors or in older patients with other health concerns. This strategy is appropriate when the tumor is small, typically less than 2 centimeters, and is causing minimal or manageable symptoms. It is also favored when the tumor has a slow or undetectable growth rate, as many acoustic neuromas are benign and grow very slowly.
The goal of this management strategy is to avoid the potential complications of intervention unless the tumor’s behavior necessitates treatment. Monitoring involves a schedule of regular contrast-enhanced Magnetic Resonance Imaging (MRI) scans and comprehensive hearing tests (audiograms). The initial MRI may be repeated six months after diagnosis, followed by annual scans to establish the tumor’s growth pattern.
Intervention is generally recommended if surveillance scans show significant tumor growth, often defined as an increase of 2 millimeters or more per year, or if symptoms worsen considerably. This approach may postpone or even eliminate the need for more aggressive treatment. For patients with serviceable hearing at the time of diagnosis, observation offers a high probability of preserving that hearing for at least a few years.
Microsurgical Tumor Removal
Microsurgical tumor removal is the only treatment option that offers the possibility of completely eradicating the acoustic neuroma. This procedure is typically reserved for tumors that are large, have demonstrated significant growth, or are causing pressure on the brainstem. The primary goal is total or near-total tumor resection while striving to preserve the function of the adjacent facial nerve and, when possible, the patient’s hearing.
Surgeons use three primary approaches, with the choice influenced by the tumor’s size, location, and the patient’s existing hearing status. The translabyrinthine approach involves removing the tumor through the mastoid bone and inner ear, which provides excellent exposure to the tumor and the facial nerve. However, this method requires sacrificing the inner ear structures, resulting in complete hearing loss in the affected ear.
The retrosigmoid, or suboccipital, approach accesses the tumor from behind the mastoid bone and is often used for tumors of various sizes, with the possibility of preserving hearing in smaller lesions. The middle cranial fossa approach is generally reserved for small tumors confined to the internal auditory canal, designed to maximize the chance of hearing preservation. All surgical approaches carry the risk of damaging the delicate facial nerve, which can lead to temporary or permanent facial weakness or paralysis. Hearing loss and balance disturbances are also common complications following the procedure.
Focused Radiation Approaches
Focused radiation therapy is a non-invasive alternative to surgery that aims to stop the tumor from growing rather than removing it immediately. The mechanism involves delivering a precise, high dose of radiation that damages the tumor cell DNA, causing the cells to cease replication and the tumor to stabilize or shrink over time. This treatment is delivered on an outpatient basis and is often favored for patients who are not suitable candidates for surgery due to their age, health, or personal preference.
Two main types of focused radiation are used for acoustic neuromas: Stereotactic Radiosurgery (SRS) and Fractionated Stereotactic Radiotherapy (FSRT). SRS, often delivered by a Gamma Knife or CyberKnife, involves a single, high-dose treatment session. FSRT delivers the total radiation dose in multiple smaller doses over several weeks, typically spread across 20 to 30 sessions.
The advantage of FSRT is that delivering the radiation in smaller fractions may allow for a higher probability of preserving functional hearing compared to single-session SRS. While focused radiation therapy avoids the immediate risks of open surgery, potential delayed side effects include temporary swelling of the tumor, which can temporarily worsen symptoms. The risk of permanent facial nerve injury is generally lower than with surgery, typically ranging from 1 to 5 percent.
Factors Guiding Treatment Selection
The decision-making process for managing an acoustic neuroma requires a thorough evaluation of several distinct factors. Tumor characteristics are paramount, including the size and location of the tumor, as well as its documented growth rate. Larger tumors, especially those compressing the brainstem, often necessitate a more aggressive intervention like microsurgery, while small, stable tumors are candidates for observation.
Patient-specific elements, such as age and overall health, heavily influence the choice, as advanced age or significant comorbidities may make the risks of surgery prohibitive. The severity and nature of the patient’s symptoms also play a role, particularly the level of existing hearing loss and the extent of balance issues. If a patient still has useful hearing, approaches like the middle fossa surgery or FSRT may be prioritized to maximize hearing preservation.
Ultimately, the choice is made through a process of shared decision-making, where the patient’s personal preferences, lifestyle, and tolerance for potential risks are considered. This comprehensive approach involves multidisciplinary consultation, typically including a neurosurgeon, an otologist or neurotologist, and a radiation oncologist. These specialists collectively weigh the goals of tumor control against the preservation of neurological function and quality of life.