Acoustic Neuroma

Acoustic neuroma, also referred to as vestibular schwannoma, is a benign tumor arising from Schwann cells of the vestibular component of the cranial nerve VIII. Acoustic neuroma forms within the internal auditory meatus and extends into the cerebellopontine angle. Vestibular schwannoma is mostly unilateral. Bilateral vestibular schwannomas are associated with neurofibromatosis type II. Symptoms arise due to compression of the cranial nerves V, VII, and VIII, and the cerebellum. The most common complaint is unilateral hearing loss but acoustic neuroma can also present with vertigo, decreased facial sensation, Bell’s palsy, and ataxia. Diagnosis of vestibular schwannoma is made with MRI of the brain with contrast. Treatment depends on the size of the tumor and symptom severity. Large tumors with severe hearing loss are treated with surgical excision or radiation therapy, while small tumors with mild symptoms can be observed over time.

Last update:

Table of Contents

Share this concept:

Share on facebook
Share on twitter
Share on linkedin
Share on reddit
Share on email
Share on whatsapp

Overview

Definition

Acustic neuroma is a benign tumor of Schwann cells that is most commonly found on cranial nerve VIII (vestibulocochlear nerve).

Classification of nervous system tumors

Table: Classification of nervous system tumors
Categories Specific tumors
Neuroepithelial tumors in the CNS
  • Astrocytomas, including glioblastoma multiforme
  • Oligodendroglioma
  • Ependymoma and choroid-plexus tumors
  • Medulloblastomas (embryonal tumors)
Meningeal tumors
  • Meningiomas
  • Hemangioblastomas
Sellar region tumors
  • Craniopharyngioma
  • Pituitary adenoma
  • Pinealoma/pinealoblastoma
Primary CNS lymphoma Primary CNS lymphoma
Metastasis to the brain (5x more common than primary brain tumors) Most commonly arising from:
  • Lung, breast, and renal cell carcinomas
  • Melanoma
Peripheral tumors
  • Schwannomas, including acoustic neuroma
  • Neuroblastoma

Epidemiology

  • Median age of diagnosis: 53 years
  • Most common tumor of cerebellopontine angle
  • Most commonly unilateral 
  • Incidence: 11 per 1 million people in the United States 
  • No difference in incidence by gender
  • Higher incidence in Asian Pacific Islanders

Etiology

  • Many cases have no known etiology.
  • Sometimes associated with mutation in long arm of chromosome 22
  • Associated with loud noises, head and neck radiation therapy, and neurofibromatosis type 2

Clinical Presentation

Symptoms of acoustic neuroma are divided into early and late phases.

Early phase

Tumor expansion in the internal auditory meatus exerting pressure on vestibulocochlear nerve (CN VIII):

  • Vestibular nerve compression:
    • Dizziness 
    • Postural imbalance
  • Cochelar nerve compression: unilateral sensorineural hearing loss (most common symptom)

Late phase

Compression of adjacent structures in the cerebellopontine angle:

  • Facial nerve compression: ipsilateral facial weakness or complete facial paralysis (Bell’s palsy)
  • Trigeminal nerve compression:
    • Decreased ipsilateral facial sensation
    • Ipsilateral facial numbness
  • Ipsilateral cerebellar compression: 
    • Ataxia
    • Dysdiadochokinesia (impaired rapid alternating movements)
    • Dysmetria

Diagnosis

Cranial nerve testing

  • Vestibulocochlear nerve: audiometry
    • Sensorineural hearing loss
    • Difficulty perceiving high-frequency sounds
  • Facial nerve:
    • Ipsilateral facial weakness
    • Ipsilateral facial twitching
  • Trigeminal nerve: 
    • Ipsilateral decreased facial sensation
    • Ipsilateral decreased corneal reflex

Imaging studies

  • MRI of the brain with contrast:
    • Initial imaging test of choice
    • Performed in patients with abnormal audiometry results and high suspicion for vestibular schwannoma
    • Findings:
      • Enhanced circular lesion in internal auditory meatus
      • Expansion into the cerebellopontine angle
      • Cystic and fat degeneration are often seen.
  • CT of the brain with contrast:
    • Performed in patients not eligible for MRI (e.g., patients with a pacemaker or metal implant)
    • Findings similar to those of MRI scan

Histopathology

  • Strongly reactive for S100
  • Hypercellular areas with spindle cells alternating with hypocellular myxoid stroma
Schwannoma histology

Schwannoma histology:
Low-power view of schwannoma illustrating the nuclear palisading (thin arrow) and the hyaline vessel walls (thick arrow). H&E stain ×300

Image: “Pathogenesis of vestibular schwannoma in ring chromosome 22.” by Denayer E, Brems H, de Cock P, Evans GD, Van Calenbergh F, Bowers N, Sciot R, Debiec-Rychter M, Vermeesch JV, Fryns JP, Legius E. License: CC BY 2.0

Management

Large tumor with severe hearing loss

  • Surgical excision:
    • Surgery cannot restore hearing loss but can prevent further loss.
    • Intraoperative monitoring of cranial nerves to reduce risk of nerve injury
    • Complications:
      • Tinnitus
      • Hearing loss
      • Facial paralysis
      • Taste changes
      • Headaches
  • Radiation therapy:
    • Stereotactic radiosurgery or fractionated stereotactic radiotherapy
    • Goal of radiation is to control the tumor, prevent further growth, and sometimes cause a reduction in tumor size.
    • Complications:
      • Facial weakness
      • Malignancy

Small tumor with minor hearing loss

Serial monitoring:

  • MRI scan every 6–12 months to track tumor progression
  • Hearing aids for hearing loss (about 50% of patients who are observed for a decade lose functional hearing)

Differential Diagnosis

  • Meningioma: benign tumor arising from the meninges of the brain or the spinal cord. Risk factors include radiation exposure. Meningioma presents with headache, vision disturbances, and possible seizures. Brain imaging and biopsy are the main diagnostic tools. Meningioma is treated with surgical excision or radiation. 
  • Neurofibromatosis type II: autosomal dominant neurocutaneous syndrome caused by NF2 gene mutation on chromosome 22. NF2 gene codes for the merlin protein. Symptoms depend on the tumors and their locations. These tumors include bilateral cataracts, bilateral acoustic neuromas, meningiomas, ependymomas, and neurofibromas. Diagnosis is made with genetic patient history, physical examination, imaging, and genetic testing. Management includes surgical excision or radiation for the tumors and hearing aids for any functional hearing loss.
  • Meniere’s disease: typically, a unilateral inner ear disorder causing a periodic sensation of spinning, tinnitus, and fullness in the ear. Symptoms seem to be caused by fluid accumulation in the inner ear’s labyrinth. The disease is considered progressive and may cause hearing loss. Diagnosis is based on clinical symptoms and hearing examination. Treatment is with antiemetics and anxiolytics (acute episodes) and includes physical therapy, dietary changes (low-salt diet), and counselling (chronic management). Unlike acoustic neuroma, there is no mass seen on imaging in Meniere’s disease.

References

  1. Park, J.K., Vernick, D.M. (2020). Vestibular schwannoma (acoustic neuroma). UpToDate. Retrieved May 23, 2021, from https://www.uptodate.com/contents/vestibular-schwannoma-acoustic-neuroma
  2. Martin, K.A. (n.d.). Patient education: Vestibular schwannoma (acoustic neuroma). UpToDate. Retrieved May 23, 2021, from https://www.uptodate.com/contents/vestibular-schwannoma-acoustic-neuroma-the-basics
  3. Kutz, J.W. (2020). Acoustic neuroma. Medscape. Retrieved May 23, 2021, from https://emedicine.medscape.com/article/882876-overview

Study on the Go

Lecturio Medical complements your studies with evidence-based learning strategies, video lectures, quiz questions, and more – all combined in one easy-to-use resource.

Learn even more with Lecturio:

Complement your med school studies with Lecturio’s all-in-one study companion, delivered with evidence-based learning strategies.

🍪 Lecturio is using cookies to improve your user experience. By continuing use of our service you agree upon our Data Privacy Statement.

Details