Tests in vestibular schwannoma

Tests in vestibular schwannoma

Hearing tests

An audiogram is a diagnostic test used to evaluate a person’s hearing ability by recording their responses to sounds of varying frequencies and intensities. Typical findings in a patient with a vestibular schwannoma may include unilateral sensorineural hearing loss, as the tumour can affect the nerves responsible for transmitting sound signals to the brain. This hearing loss is often characterized by a downward-sloping pattern on the audiogram, with poorer hearing at higher frequencies (1).

A word recognition score is another test that assesses a person’s ability to understand speech in noisy environments. A decreased word recognition score may be observed in a patient with a vestibular schwannoma due to auditory nerve compression or damage caused by the tumour. This can be indicative of sensorineural hearing loss (2).

“Roll-over” refers to a phenomenon where the understanding of speech deteriorates as the intensity of the sound increases. In patients with a vestibular schwannoma, speech discrimination roll-over may occur due to distortion of sound signals by the tumour, leading to difficulty distinguishing speech sounds at higher volumes (3).

IMG_2348

Auditory brainstem response

The auditory brainstem response (ABR), otherwise known as brainstem evoked response audiometry (BERA), is a test that measures the electrical activity in the auditory nerve and brainstem in response to sound stimuli. During the test, electrodes are placed on the scalp to record the neural responses to clicks or tones presented through headphones. The test can help diagnose hearing loss, auditory nerve disorders, and vestibular schwannoma, a benign tumour that affects the vestibulocochlear nerve (4).

In cases of vestibular schwannoma, the ABR test typically shows an asymmetry in the waveforms, with delayed or absent responses on the affected side. This is due to the tumour compressing the vestibulocochlear nerve and disrupting the normal transmission of auditory signals to the brainstem. Other findings may include elevated hearing thresholds, reduced amplitudes of the waveforms, and prolonged latencies. These results, along with other diagnostic tests such as MRI, help accurately diagnose and manage vestibular schwannoma (5).

Vestibular tests

VHIT (Video Head Impulse Test) is a test that evaluates the function of the semicircular canals in the inner ear by measuring the eye movements in response to head movements. A reduced or absent vestibulo-ocular reflex can be observed in patients with vestibular schwannoma (6).

A video head impulse test (VHIT)
A video head impulse test (VHIT)

O VEMP (ocular vestibular-evoked myogenic potential) and c VEMP (cervical vestibular-evoked myogenic potential) tests assess the function of the otolithic organs and nerve pathways in the inner ear. In patients with vestibular schwannoma, abnormalities in VEMPs may be present, indicating which nerve division is affected (7).

 

Cervical vestibular evoked myogenic potentials (cVEMP)
A patient undergoing a cVEMP test.

The caloric test involves irrigating the ear canals with warm and cold water to stimulate the vestibular system. Abnormal responses, such as decreased response or directional preponderance, may be seen in patients with vestibular schwannoma (8).

A caloric test
A caloric test

Nystagmus, a rapid involuntary eye movement, may also be present in patients with vestibular schwannoma. The direction and characteristics of nystagmus can provide valuable information about the location and severity of the tumour (9).

Central oculomotor tests assess the integrity of the central nervous system pathways involved in eye movements. Abnormal findings in these tests may suggest central involvement of the vestibular schwannoma (10).

Magnetic resonance imaging (MRI)

MRI, or magnetic resonance imaging, is a diagnostic imaging technique that uses strong magnetic fields and radio waves to create detailed images of the body. MRI is commonly used in the evaluation of vestibular schwannoma. It is regarded as the gold standard investigation (11).

On MRI, vestibular schwannomas typically appear as enhancing masses that can vary in size and shape. A VS as small as 2 mm can be diagnosed on an MRI. They may also compress nearby structures, such as the brainstem or cerebellum. Additionally, MRI can help determine the extent of the tumour and assist in planning for surgical or radiation therapy.

Other typical findings in vestibular schwannoma on MRI include:

  • Displacement of the 4th ventricle.
  • Effacement of the cerebellopontine angle cistern.
  • Enlargement of the internal auditory canal.

MRI can also help differentiate vestibular schwannomas from other causes of vestibular symptoms, such as acoustic neuromas or meningiomas.

Intracannaliculur acoustic neuroma
Vestibular schwannoma often causes tinnitus

Genetic testing

Genetic testing can play a crucial role in diagnosing and managing vestibular schwannoma, a type of tumour affecting the vestibular nerve (12). By analyzing the tumour’s genetic makeup, healthcare providers can determine the specific mutations that are driving its growth, which can help guide treatment decisions. In some cases, genetic testing may uncover an underlying genetic predisposition to developing vestibular schwannomas, such as in patients with neurofibromatosis type 2 (NF2). This information is valuable for identifying at-risk individuals, monitoring disease progression, and potentially developing targeted therapies for improved outcomes.

References

1. Kim SH, Lee SH, Choi SK, Lim YJ, Na SY, Yeo SG. Audiologic evaluation of vestibular schwannoma and other cerebellopontine angle tumors. Acta Otolaryngol. 2016;136(2):149-53. doi: 10.3109/00016489.2015.1100326. Epub 2015 Oct 19. PMID: 26479426.

2. Warrick P, Bance M, Rutka J. The risk of hearing loss in nongrowing, conservatively managed acoustic neuromas. Am J Otol. 1999 Nov;20(6):758-62. PMID: 10565721.

3. Hannley M, Jerger J. PB rollover and the acoustic reflex. Audiology. 1981;20(3):251-8. doi: 10.3109/00206098109072699. PMID: 7213210.

4. Eggermont JJ. Auditory brainstem response. Handb Clin Neurol. 2019;160:451-464. doi: 10.1016/B978-0-444-64032-1.00030-8. PMID: 31277868.

5. Matthies C, Samii M. Management of vestibular schwannomas (acoustic neuromas): the value of neurophysiology for evaluation and prediction of auditory function in 420 cases. Neurosurgery. 1997 May;40(5):919-29; discussion 929-30. doi: 10.1097/00006123-199705000-00007. PMID: 9149249.

6. West N, Sass H, Klokker M, Cayé-Thomasen P. Video Head Impulse Test Results in Patients With a Vestibular Schwannoma-Sensitivity and Correlation With Other Vestibular System Function Tests, Hearing Acuity, and Tumor Size. Otol Neurotol. 2020 Jun;41(5):e623-e629. doi: 10.1097/MAO.0000000000002600. PMID: 32118807.

7. Rosengren SM, Colebatch JG, Young AS, Govender S, Welgampola MS. Vestibular evoked myogenic potentials in practice: Methods, pitfalls and clinical applications. Clin Neurophysiol Pract. 2019 Feb 26;4:47-68. doi: 10.1016/j.cnp.2019.01.005. PMID: 30949613; PMCID: PMC6430081.

8. Brown CS, Peskoe SB, Risoli T Jr, Garrison DB, Kaylie DM. Associations of Video Head Impulse Test and Caloric Testing among Patients with Vestibular Schwannoma. Otolaryngol Head Neck Surg. 2019 Aug;161(2):324-329. doi: 10.1177/0194599819837244. Epub 2019 Mar 26. PMID: 30909803.

9. Lloyd SK, Baguley DM, Butler K, Donnelly N, Moffat DA. Bruns’ nystagmus in patients with vestibular schwannoma. Otol Neurotol. 2009 Aug;30(5):625-8. doi: 10.1097/MAO.0b013e3181a32bec. PMID: 19471169.

10. Huygen PL, Hoogland GA. Vestibular and ocular motor manifestations of cerebellopontine angle tumours. Adv Otorhinolaryngol. 1984;34:57-70. doi: 10.1159/000409836. PMID: 6393737.

11. Robson AK, Leighton SE, Anslow P, Milford CA. MRI as a single screening procedure for acoustic neuroma: a cost effective protocol. J R Soc Med. 1993 Aug;86(8):455-7. PMID: 8078042; PMCID: PMC1294049.

12. Goetsch Weisman A, Weiss McQuaid S, Radtke HB, Stoll J, Brown B, Gomes A. Neurofibromatosis- and schwannomatosis-associated tumors: Approaches to genetic testing and counseling considerations. Am J Med Genet A. 2023 Oct;191(10):2467-2481. doi: 10.1002/ajmg.a.63346. Epub 2023 Jul 24. PMID: 37485904.