Acoustic neuroma


Called vestibular schwannoma (VS), is the preferred term.

A common benign intracranial tumor of the myelin forming cells of the vestibulocochlear nerve.

Derived from the Schwann cells of the vestibular portion of the eighth cranial nerve.

Vestibular schwannoma is a benign tumor that arises from Schwann cells of the vestibular branch of the VIII nerve in more than 90% of cases; less than 10% arise from the cochlear branch of VIII.

Estimated to represent 8% of all intracranial tumors, and are the most common neoplasm of the cerebrop ontine angle.

The most common neoplasm of the cerebropontine angle in adults.

Involves the vestibular portion of the VIIIth cranial nerve.

It arises from the myelinated  Schwann cells of the cranial nerve VIII.
Arises from the Schwann cells.

Approximately 3000 cases diagnosed each year in the U.S.

Worldwide prevalence 1 in 100,000 population.

Lifetime prevalence exceeds 1 case among 500 people.

Clinically presents with hearing loss, tinnitus, dysequilibrium, with greater than 80% of cases having some degree of unilateral hearing loss before diagnosis.

Vestibular schwannoma, if untreated progressive unilateral hearing loss develops in nearly all patients. 

Hearing loss is often preceded by difficulty with speech discrimination, especially when the patient is talking on the telephone. 

Tinnitus (70%) and unsteady gait (70%) are also common. 

Further tumor growth can cause facial numbness (30%) or, less often, facial weakness, loss of taste, and otalgia due to encroachment on the trigeminal and facial nerves. 

Larger tumors grow into the cerebellopontine angle, causing headache, nausea, vomiting, diplopia, and ataxia or increased intracranial pressure and hydrocephalus. 

Other signs include nystagmus and cerebellar ataxia. 

The constellation of late symptoms can develop with any mass in the cerebellopontine angle; however, only vestibular schwannomas present with initial symptoms of tinnitus or hearing dysfunction. 

Accounts for 5-10% of intracranial tumors in adults.

Peak incidence 5th to 6th decades.

Current incidence 3-5 cases per 100,000 person-years.
Detection increased by neurodiagnostic imaging.
Dramatic increase among individuals over age 70 years, with incidence approaching 20 cases per 100,000 person-years.
Today, diagnosis common in 6-7th decades, with tumors just millimeters in greatest diameter.

Increase detection, often incidentally, when the tumor is small and the patient is at advanced age, shifting towards more conservative approach.

Genders are equally affected.

Unilateral sporadic VS accounts for more than 95% of cases.

May occur sporadically or as part of von Recklinghausen’s disease.

Two forms associated with von Recklinghausen’s disease: Neurofibromatosis type I and Neurofibromatosis type II.

Bilateral tumors occur in less than 5% of patients and, when present, are diagnostic for NF-2.

Treatment options are based on the patient’s symptoms and tumor site.

Treatment is controversial and varied.

Treatments can range from surveillance with MRI examinations to radiation therapy or surgery.

Microsurgery is the treatment of choice for large vestibular schwannomas.

Tumor size at the time of diagnosis has decreased over time, and most newly diagnosed tumors of small or medium sized.

Conservative management with symptom control and follow up with MRIs is more suitable for patients with small to medium-sized esions, especially in the elderly.

Hearing status helps to decide whether to observe or to take more aggressive treatment measures.

Following patients by annual scans during the first three-to five years after diagnosis and therefore can be followed every two years until 10 years after the presentation.

Approximately half of the patients who are observed will have some type of hearing loss and treatment can be chosen based on their clinical manifestations.

Sudden hearing loss can be present and up to 26% of patients with acoustic neuromas.

Tinnitus present in 53-70% of patients and is most commonly ipsilateral.

Vertigo has been found up to 58% of patients with acoustic neuroma and can’t occur early in the disease process.

Vestibular schwannomas grow slowly into the internal auditory meatus and the cerebellopontine angle, displacing the adjacent cerebellum, pons, or cranial nerves (usually V and VII).

Because they grow slowly, many tumors are large and even cystic before they become symptomatic.

The growth rate may increase during pregnancy.

Sequelae include this equilibrium, trigeminal nerve dysfunction, headache, facial nerve abnormalities, hoarseness, dysphasia, and dysarthria.

Stereotactic radiation is a useful primary management alternative for patients with cerebellopontine angle and/or skull base tumors, including acoustic neuromas, meningiomas, and paragangliomas.

Increasingly used for secondary management of recurrent or residual disease.

Fractionated stereotactic radiation for acoustic tumors developed in part because of the relatively high incidence of trigeminal and facial nerve palsies that occurred after treatment with single-dose stereotactic radiation and in part as an extension of traditional fractionated radiotherapy regimens onto which stereotaxy was applied.

Fractionated stereotactic radiation offers high control rates while avoiding the morbidity frequently observed after single-dose stereotactic radiation or microsurgery.

Traditionally, fractionated therapy has been considered to be associated with fewer cranial nerve complications than single-dose treatment.

It is suggested that the use of multiple smaller-dose fractions over a longer period perhaps gives the greatest possibility of hearing preservation, avoidance of facial palsy, and tumor control.

Use of multiple-dose fractionated radiation therapy results in potentially larger areas receiving multiple low doses of radiation offsetting any radiobiological advantage of fractionation.

No distinct advantage to either traditionally fractionated, hypofractionated, or non-fractionated techniques, appears with regards to tumor control, posttreatment cranial neuropathy, or other postirradiation complications

Fractionated stereotactic radiotherapy does seem to confer a slight advantage towards hearing preservation compared to non-fractionated modalities.

A small but definite risk of malignant transformation of tumor and or secondary malignancy from irradiation exists.

Comparing stereotactic radiation with microsurgery, there is less cost for radiation treatment of acoustic tumors smaller than 3 cm in diameter.

There are comparable results in terms of postoperative outcomes, as of 5-10 years for most gamma knife studies and 3-4 years for LINAC based fractionated treatment studies.

Lower risks of treatment complications over microsurgery in the acute setting, stereotactic radiotherapy is advantageous as a treatment modality in patients who are older, medically infirm, requiring anticoagulant therapy, or otherwise poorer surgical or anesthetic candidates.

The advantages of stereotactic radiotherapy, whether fractionated, hypofractionated, or single-dose, in the acute setting are offset by the long-term rates of cranial neuropathy and hearing loss eventually prevalent, which are comparable to those seen following microsurgery.

Brainstem compression by acoustic tumor is not improved by radiation, so surgery is the pref2242ed option for such patients with brainstem compressive or hydrocephalic tumors.

Patients with significant dysequilibrium or recurrent vertigo are not improved and may actually worsen by stereotactic radiation.

In summary, patients who have serviceable hearing, no vertigo, and a non-brainstem-compressive or non-hydrocephalic acoustic tumor 2 cm in diameter or smaller are good candidates for stereotactic radiotherapy.

Stereotactic radiotherapy minimizes risk in tumor treatment such as those associated with craniotomy and microsurgery procedures.

Stereotactic radiotherapy’s exposure to radiation puts patients at higher risk of subacute, long-term, or latent complications that microsurgery and definitive resection avoid.

Patients who undergo gamma knife radiosurgery for acoustic neuroma, have a quality of life comparable to population norms at long-term follow-up.

Among patients with newly diagnosed small and medium sized vestibular schwannoma, upfront radiosurgery demonstrated greater tumor volume reduction at four years, then await and scan approach with treatment upon tumor growth (V-REX trial investigators).

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