Vestibular tumor

Template:Vestibular tumor Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

Vestibular tumors are growths that tend to develop in or outside the auditory canal. They may be found anywhere between the chin and the larynx (or voicebox) and are not more inclined to one side of the body than the other. They are predominantly present in adolescent females though they are not directly related to any hygienal issues. While surgery is the most often cure, deaths rarely occur due to the existence of vestibular tumors.

The first reported case of a vestibular tumor was in 1898 in Lancaster, Pennsylvania. Though there have been stories of growths of the like of vestibular tumors, this was the first medically reported case. At the time, surgery was too dangerous, so Emilia Walfen was forced to live with the tumor, which eventually grew to the size of a Concord grape.

Recent studies in NF2 patients led to the identification of the neurofibromin 2 gene, which is located on chromosome 22. The NF2 gene produces merlin, also known as schwannomin, a cell membrane-related protein that acts as a tumor suppressor. Bi-allelic inactivation of the NF2 gene is found in most sporadic vestibular schwannomas.

• Vestibular schwannomas arise from perineural elements of the Schwann cell.
• They occur with equal frequency on the superior and inferior branches of the vestibular nerve.
• Microscopically, zones of alternately dense and sparse cellularity, called Antoni A and B areas, respectively, are characteristic of vestibular schwannomas.
• Malignant degeneration is extremely rare, with only six cases having been reported.
• Immunohistochemical staining for S100 protein is usually positive in both the benign and the rare malignant forms of this tumor.

The differential diagnosis includes meningioma, facial nerve schwannomas, gliomas, cholesterol cysts, cholesteatomas, hemangiomas, aneurysms, arachnoid cysts, lipomas, and metastatic tumor. For more information click here On the basis of seizure, visual disturbance, and constitutional symptoms, meningioma must be differentiated from oligodendroglioma, astrocytoma, hemangioblastoma, pituitary adenoma, schwannoma, primary CNS lymphoma, medulloblastoma, ependymoma, craniopharyngioma, pinealoma, AV malformation, brain aneurysm, bacterial brain abscess, tuberculosis, toxoplasmosis, hydatid cyst, CNS cryptococcosis, CNS aspergillosis, and brain metastasis.

ABBREVIATIONS

CNS=Central nervous system, AV=Arteriovenous, CSF=Cerebrospinal fluid, NF-2=Neurofibromatosis type 2, MEN-1=Multiple endocrine neoplasia, GFAP=Glial fibrillary acidic protein, HIV=Human immunodeficiency virus, BhCG=Human chorionic gonadotropin, ESR=Erythrocyte sedimentation rate, AFB=Acid fast bacilli, MRA=Magnetic resonance angiography, CTA=CT angiography

Common risk factors for the development of vestibular schwaomas include:

• Childhood exposure to low-dose radiation for benign conditions of the head and neck
• Radiofrequency exposure from the use of mobile phones
• Excessive noise exposure

• The overall incidence of vestibular schwannomas is approximately 1 per 100,000 person-years in the United States.
• Bilateral vestibular schwannomas are primarily observed in patients with neurofibromatosis type 2 (NF2).
• The tumors are unilateral in more than 90 percent of cases, affecting the right and left sides with equal frequency.

• The median age at diagnosis is approximately 50 years.

• Vestibular schwannomas occur equally in both genders.

Vestibular schwanama pose a major health impediment if left untreated as they might cause pressure on adjacent posterior fossa structures such as cerebellum or brainstem and result in ataxia, brainstem compression, cerebellar tonsil herniation, hydrocephalus, and death can occur in untreated cases. Common complication include seizures and paralysis difficulty swallowing due to the pressure on the tongue or pharynx. The functions of the lower cranial nerves can also become impaired, leading to dysarthria, dysphagia, aspiration, and hoarseness.

• Symptoms associated with vestibular schwannoma can be due to cranial nerve involvement, cerebellar compression, or tumor progression. Clinical manifestations in this series included the following:

• Hearing tests are typically abnormal due to involvement of the acoustic nerve.
  • The Weber and Rinne tests may be useful in suggesting asymmetric sensorineural hearing impairment.

• Neurologic examination may reveal other cranial nerve deficits
  • A decreased or absent ipsilateral corneal reflex and facial twitching or hypesthesia may occur as cranial nerves V and VII become affected.
  • Romberg, Hall-Pike, and other common office balance tests are typically normal.

Findings of vestibular schwanoma on CT include:

• Erosion and widening of the internal acoustic canal.
• The density of these tumors on non-contrast imaging is variable, and often they are hard to see, especially on account of beam hardening and streak artefact from the adjacent petrous temporal bone.

• Contrast enhancement is present but can be underwhelming, especially in larger lesions with cystic components.

MRI findings of vestibular schwanoma include:

Audiometry

• Audiometry is the best initial screening laboratory test for the diagnosis of vestibular schwannoma.
• Pure tone and speech audiometry should be performed in an acoustically shielded area.
• Test results typically show an asymmetric sensorineural hearing loss, usually more prominent in the higher frequencies.
• Hearing loss does not necessarily correlate with tumor size.
• The speech discrimination score is usually markedly reduced in the affected ear and out of proportion to the measured hearing loss.
• Common audiometry tests that are of current practice include:
  • Acoustic reflex testing
  • Impedance audiometry
  • Bekesy audiometry
  • Brainstem-evoked response audiometry (AER/ABR).

Vestibular testing

• Vestibular testing has limited utility as a screening test for the diagnosis of vestibular schwannoma because of the accuracy of evoked response audiometry.
• When testing is performed, a decreased or absent caloric response on the affected side may be seen. When the tumor is small, though, a normal response is often seen.

Treatment options for patients with a vestibular schwannoma include surgery and radiation therapy.

Surgery generally results in satisfactory long-term control of vestibular schwannomas. There are three standard operative approaches.

Radiation therapy for patients with vestibular schwannoma include stereotactic radiosurgery (SRS), stereotactic radiotherapy (SRT), and proton beam therapy, as well as conventional fractionated radiation therapy.