Vestibular tumor

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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]

Overview

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.

Historical Perspective

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.

Pathogenesis

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.

Microscopic pathology

  • 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.

Differentiating Vestibular schwannoma from other diseases

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.

Diseases Clinical manifestations Para-clinical findings Gold
standard
Additional findings
Symptoms Physical examination
Lab Findings MRI Immunohistopathology
Head-
ache
Seizure Visual disturbance Constitutional Focal neurological deficit
Adult primary brain tumors
Meningioma
+ +/− +/− +
  • Well circumscribed
  • Extra-axial mass
  • Whorled spindle cell pattern
  • May be associated with NF-2
Glioblastoma multiforme
+ +/− +/− +
  • Pseudopalisading appearance
Oligodendroglioma
+ + +/− +
  • Chicken wire capillary pattern
  • Fried egg cell appearance
Hemangioblastoma
+ +/− +/− +
Pituitary adenoma
[1]
+ Bitemporal hemianopia
  • It is associated with MEN1 disease.
Schwannoma
+
  • Split-fat sign
  • Fascicular sign
  • Often have areas of hemosiderin
  • S100+
Primary CNS lymphoma
+ +/− +/− +
  • Single mass with ring enhancement
Childhood primary brain tumors
Pilocytic astrocytoma
+ +/− +/− +
Medulloblastoma
+ +/− +/− +
  • Homer wright rosettes
Ependymoma
[1]
+ +/− +/− +
  • Hydrocephalus
  • Causes an unusually persistent, continuous headache in children.
Craniopharyngioma
[1]
+ +/− + Bitemporal hemianopia +
Pinealoma
+ +/− +/− + vertical gaze palsy
  • May cause prinaud syndrome (vertical gaze palsy, pupillary light-near dissociation, lid retraction and convergence-retraction nystagmus
Vascular
AV malformation
[1]
+ + +/− +/−
Brain aneurysm
+ +/− +/− +/−
  • MRA and CTA
Infectious
Bacterial brain abscess
+ +/− +/− + +
  • Central hypodense signal and surrounding ring-enhancement in T1
  • Central hyperintense area surrounded by a well-defined hypointense capsule with surrounding edema in T2
  • History/ imaging
Tuberculosis
[1]
+ +/− +/− + +
  • Lab data/ Imaging
Toxoplasmosis
+ +/− +/− +
  • History/ imaging
Hydatid cyst
[1]
+ +/− +/− +/− +
  • Imaging
CNS cryptococcosis
+ +/− +/− + +
  • We may see numerous acutely branching septate hyphae
  • Lab data/ Imaging
CNS aspergillosis
+ +/− +/− + +
  • Multiple abscesses
  • Ring enhancement
  • Peripheral low signal intensity on T2
  • We may see numerous acutely branching septate hyphae
  • Lab data/ Imaging
Other
Brain metastasis
[1]
+ +/− +/− + +
  • Based on the primary cancer type we may have different immunohistopathology findings.
  • History/ imaging

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

Risk Factors

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

Epidemiology and Demographics

Incidence

  • 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.

Age

  • The median age at diagnosis is approximately 50 years.

Gender

  • Vestibular schwannomas occur equally in both genders.

Natural History, Complications, and Prognosis

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.

Diagnosis

History and Symptoms

  • 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:
Never involvement Incidence Symtpoms
Cochlear nerve 95 percent
Vestibular nerve 61 percent
  • Unsteadiness while walking
  • Brief tilting or veering
Trigeminal nerve 17 percent
Facial nerve 6 percent
Tumor progression

Physical Examination

CT

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

MRI findings of vestibular schwanoma include:

MRI findings of Vestibular Schwanoma
T1
  • Slightly hypointense to the adjacent brain.
  • Isointense to the adjacent brain
  • May contain hypointense cystic areas
T2
    • Heterogeneously hyperintense to adjacent brain
    • Fluid intensity cystic areas
    • May have associated peritumoral arachnoid cysts
T1 C+ (Gd) Contrast enhancement is intense however, heterogeneous in larger tumors

Other Diagnostic Studies

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:

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

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

Surgery

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

Surgery
Retromastoid suboccipital (retrosigmoid) The suboccipital approach can be used for any size tumor with or without attempted hearing preservation.
Translabyrinthine The translabyrinthine approach has been recommended for acoustic tumors larger than 3 cm and for smaller tumors when hearing preservation is not an issue.
Middle fossa The middle fossa approach is suitable for small (<1.5 cm) tumors when hearing preservation is a goal.

Radiation therapy

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.

Radiation therapy
Stereotactic radiosurgery
  • SRS is a technique that utilizes multiple convergent beams to deliver a high single dose of radiation to a radiographically discrete treatment volume, thereby minimizing injury to adjacent structures.
  • This can be accomplished with either the gamma knife or a linear accelerator.
  • Radiosurgery is a viable treatment option for selected patients with smaller tumors (<3 cm) or for enlarging tumors in patients who are not candidates for surgery
Stereotactic radiotherapy
  • Fractionated SRT utilizes focused doses of radiation given over a series of treatment sessions.
  • The intent is to reduce radiation injury to critical neural structures while preserving tumor control.
Proton beam therapy
  • Proton beam therapy may provide maximal local tumor control while minimizing cranial nerve injuries.
  • The physical characteristics of the beam result in the majority of the energy being deposited at the end of a linear track (the Bragg peak), with the dose falling rapidly to zero beyond the Bragg peak.
  • Thus, the use of proton beam therapy permits the delivery of high doses of radiation therapy to the target volume while limiting the "scatter" dose received by surrounding tissues.

References


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