Approach

Factors influencing management chiefly include tumor size, provider biases/expertise, and patient-related factors including hearing status, age, general health, and patient preference.

Management decisions

Management includes observation with serial imaging as well as active treatment with radiosurgery or microsurgery.​[12][49]​​​​ The choice of management approach depends on factors such as age of the patient, size of the tumor, extent of hearing loss, and presence of comorbidities. Surgery is often the preferred treatment option for younger patients and for patients with larger tumors, whereas observation or stereotactic radiation is often the preferred treatment option for older patients and for patients with smaller or asymptomatic tumors.[50]​ One retrospective cohort study reports that the number of patients undergoing conservative management has increased because of earlier detection using imaging techniques.[16]​ Likewise, another retrospective review states that the number of patients undergoing surgical resection has decreased by 36% from 2001 to 2014 in the US.[51]

Smaller tumors in patients with minimal symptoms (e.g., mild hearing loss) may be followed up with serial scanning, especially if there is no documented growth.

Alternatively, upfront treatment for small tumors may be undertaken in certain cases, such as in young adults, with the goal of trying to preserve hearing long term.[50] Care should be individualized, with patient preference taken into consideration. Indeed, in many developed countries, observation is the most prevalent initial management strategy among patients with tumors <1.5 cm in cerebellopontine angle diameter. Most providers recommend upfront treatment following detection of tumors >1.5 cm.

Important issues to consider include:

  • Approximately half of small vestibular schwannomas exhibit growth following diagnosis within the first 3-5 years, while approximately half remain stable. Studies using volumetric analysis, a more sensitive measure for changes in tumor size, identify higher rates of growth compared to studies using linear diameter assessments.[40]

  • There are no strong predictors for future growth, aside from larger tumor size at diagnosis.

  • Progression of a patient's symptoms is not a reliable indicator of growth.

  • Smaller tumors carry lower risk from treatment (fewer risks to facial nerve and hearing).

  • Younger patients with fewer comorbidities may respond better to treatment.

  • Tumor treatment is unlikely to improve hearing, tinnitus, headache, dizziness, or quality of life.

Depending on the tumor size and configuration, level of hearing loss, and experience of treating physicians, hearing preservation rates can vary greatly. Generally, hearing preservation microsurgery is only usually considered realistic in patients with small tumors and good baseline hearing. Hearing preservation rates with surgery range between 10% and 70% and depend on tumor size, degree of tumor extension into the internal auditory canal, baseline hearing, and provider expertise.[52][53][54]​​​​​​ Most data indicate that radiosurgery results in accelerated hearing loss compared with observation alone, or at least does not prevent future hearing loss.[55]​ Among initially observed tumors, if there is radiologic evidence of persistent tumor growth or patient preference toward intervention, treatment is recommended.

Older patients with slow-growing tumors have an option of continued observation only in selected cases.[2][32][33][35]​​[50][56]​​​[57]

At 6 months from presentation, patients who are being observed only should have an MRI, followed by yearly scans for several subsequent years, then biennially (every 2 years).[58]

More recent evidence supports the option of continued observation for selected people with small, slow-growing tumors that are mainly confined to the internal auditory canal, based on the understanding that treatment often does not improve symptoms and outcomes with radiosurgery or microsurgery are generally not influenced by limited growth.[57][59]​ With this approach, an absolute size threshold of approximately 1.5 cm in the cerebellopontine angle, rather than mere presence of growth, encourages treatment. This option may be particularly attractive for people with small tumors and asymptomatic or minimally symptomatic disease, when reliable follow-up can be assured.[57][59]

Radiation and surgery

Treatment choices include focused radiation (stereotactic radiation therapy and stereotactic radiosurgery) and surgery. Chemotherapy or medical therapy is not currently widely used for sporadic vestibular schwannomas and is generally only a consideration for patients with neurofibromatosis-related schwannomatosis. Stereotactic radiosurgery is performed in 1-5 fractions. A cranial fixation frame is often attached to the patient's head by screws placed into the skull under local anesthetic. Alternatively, a molded mask may be used to avoid the mild discomfort of head frame placement. Stereotactic radiation therapy refers to the use of multiple small doses of radiation (usually 25-30 fractions), which affect the tumor to a greater degree than surrounding normal tissue. Stereotactic radiation therapy is completed with a relocalizable face mask and does not require frame fixation.[60][61][62][63]

Surgery is completed with a number of approaches tailored to the patient's tumor size and degree of hearing loss, and to the surgeon's experience. In general, a middle fossa approach is completed through an incision that begins in front of the tragus of the affected ear and extends superiorly onto the temporal scalp. A 5 x 5 cm craniotomy is made above the ear, essentially centered on the ear canal. This approach is typically reserved for smaller tumors confined to the internal auditory canal when hearing preservation is attempted.[64] The translabyrinthine approach is performed through an incision behind the ear, working through the mastoid portion of the temporal bone, and does not preserve hearing because the inner ear is opened when, as the name suggests, the labyrinthine bone is drilled away. Thus, this approach is often used for patients who already have poor hearing or sometimes in cases where hearing preservation is unlikely, such as with large tumors.[64] The retrosigmoid approach is completed through an incision behind the ear allowing a craniotomy or craniectomy inferior to the transverse sinus and posterior to the sigmoid sinus.[64] This approach can be used for any sized tumor, with or without the intent of hearing preservation. Almost always, the posterior aspect of the internal auditory canal must be removed with a high-speed drill to access the component of the tumor extending into this area.[65][66][67]​​​ Intraoperative neurophysiologic monitoring of cranial nerves, in particular the facial nerve, is considered standard of care. Monitoring of cranial nerves has changed the nature and success of surgery in terms of cranial nerve morbidity.[68][69][70][71]

In approximately 5% to 10% of patients who opt for radiation therapy, tumors may grow despite treatment and may require salvage surgery.[72] Similarly, in patients selected for surgical treatment, tumor recurrence may occur during follow-up, especially if less than a gross total resection is performed, and then may require follow-up salvage radiation.

Small tumor (Koos grades 1-2)

Small, asymptomatic tumors with normal cranial nerve function can be monitored by observation. Some of these patients may prefer active treatment and opt for focused radiation or surgery; however, surgery and microsurgery can deteriorate the nerve function and are usually not recommended from the outset.[13]​ In patients with small tumors with complete hearing loss, observation is considered the first option. Such patients can also benefit from focused radiation or surgery.[13]

In general, continued clinical observation is recommended if no growth appears on initial scans. If tumor growth is apparent on serial scans, focused radiation or surgery is usually recommended. The choice depends on local physician expertise and patient preference.[73][74]​ In select cases, patients with smaller growing tumors may still be observed if reliable follow-up can be assured.[57]​ In a small proportion of patients who opt for radiation therapy, tumors may grow despite treatment and may require salvage surgery.[72] Recurrence after microsurgical resection of small tumors is approximately 1% to 3% but may be slightly higher in cases of attempted hearing preservation.

Medium tumor (Koos grades 3-4; tumor size <3 cm)

A majority of patients with medium-sized tumors may have vestibular/cochlear symptoms.[13] Upfront treatment with radiosurgery or microsurgery is typically recommended for such tumors, and long-term observation is usually not considered. The reason for this paradigm is that treatment outcomes are primarily driven by tumor size, and tumors >1.5 cm risk poorer outcomes if further growth occurs.[57]​ Stereotactic radiation carries lower risk than surgery. Nevertheless, surgery ensures complete resection of the tumor.[13]

Large tumor (Koos grades 3-4; tumor size >3 cm)

With or without tumor growth on serial scans, surgery is recommended owing to the large size and potential damage to adjacent structures and resulting functional deficits. Surgery is recommended in most centers in preference to radiation, because of improvement in mass effect symptoms offered by surgery over radiation.[66][75]​​ Surgery to preserve hearing is not offered by most surgeons as the mass effect of such a large tumor often has already caused damage to hearing structures, although if the patient has useful hearing prior to surgery, a hearing preservation attempt is a reasonable undertaking, albeit not likely to succeed.​[53][67]​​ Surgery should focus on improving or maintaining quality of life and attempting to preserve the nerve function.[76]

Patients with large tumors may have modest brainstem compression and may present with facial nerve paresis and gait ataxia. Decompression of the brainstem and stretched cranial nerves is vital in such cases, and thus surgery is the preferred treatment option. Incomplete resection followed by radiation or observation is recommended, as complete resection may lead to deterioration of cranial nerve function.[13]

Management of tumors in the only hearing ear

In the uncommon situation where a patient presents with a tumor in the only hearing ear, considerations include: preparing and counseling the patient for the likelihood of complete hearing loss; maneuvers for improving hearing in the contralateral ear (including cochlear implants); brainstem auditory implants at the time of surgery in the affected last hearing ear; and cochlear implants in the ear in those with an intact cochlear nerve.[77] Detailed discussion of the management of these patients is not within the scope of this topic.

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