Acoustic Neuroma- Symptoms, Causes, Diagnosis

Introduction

Cell division is the process of multiplication of the cells followed by cell differentiation and cell growth. The group of cells are collectively called tissues and the abnormal growth of tissue in an organism is known as a tumour. The tumours usually develop due to some disturbances in the cell growth and formation of new cells. A tumour is benign (non-cancerous) when the growth is limited and it becomes malignant (cancerous) when it invades the major parts of the body.

What is Acoustic Neuroma?

Acoustic neuroma is a rare, non-malignant tumour and is also known as Vestibular Schwannoma. It emerges from Schwann cells that wrap and support the nerves. The tumours are developed on the branches of the cranial nerve VIII (also called vestibulocochlear nerve) formed by the vestibular and auditory nerves responsible for balance and hearing respectively. If the growth of the tumour is large and continuous, it becomes a serious case.

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Figure 1. Acoustic neuroma

Causes of Acoustic neuromas

• Acoustic neuroma results from a rare genetic disorder called neurofibromatosis type 2 in some individuals that commonly involves the growth of tumours on the nerves due to the presence of a defective gene on chromosome 22.

• Only 5% of the patients with neurofibromatosis type 2 report an acoustic neuroma case.

• The precise causes of acoustic neuroma are not known in most cases. Still, some risk factors such as family history, exposure to radiation, age, and exposure to loud noise are considered to be the cause.

Symptoms of Acoustic neuroma

The growth of tumours in the vestibulocochlear nerve can disturb the balance along with other complications. The symptoms of such tumorous growth are as follows:

Hearing impairment

• In 90% of people, acoustic neuromas develop a certain degree of hearing loss.

• The hearing loss can occur from straining of the nerve by the tumour or by the release of substances that are toxic to hearing.

Tinnitus

• Tinnitus is a condition in which the patient hears a high-pitched hissing or buzzing sound in the ear. Sometimes tinnitus becomes constant.

• Tinnitus may or may not be accompanied by hearing loss.

Vertigo and loss of balance

• The development of a tumour on the balance and auditory nerve results in vertigo i.e. a sudden feeling of tilting and spinning of the head.

• The patient may feel dizzy and lurch due to the loss of balance.

Fullness of ear

• A patient with acoustic neuroma may feel full ear as if water is retained in the ear canal. This usually occurs due to hearing loss.

Other symptoms

• Facial numbness, headache, nausea, change in taste, and difficulty in swallowing, are some other symptoms associated with acoustic neuroma.

Diagnosis of Acoustic neuroma

The diagnosis of acoustic neuroma generally starts with the examination of the ear followed by an assessment of hearing capacity, imaging, and the patient’s medical history. Brain scans using Magnetic Resonance Imaging (MRI) or Computerised Tomography (CT) can be used for the identification of tumours.

The following evaluations are important for the diagnosis of Acoustic neuroma;

Audiometry

It is a painless hearing test performed by an audiometer that measures the ability to hear based on the loudness of sound and the speed of vibrations.

Pure Tone Average (PTA)

It is the measurement that evaluates the hearing impairment for understanding speech. A higher score indicates a hearing loss.

Speech Reception Threshold (SPT)

It is the minimum speech level that the patient can hear 50% of the time. Similar to PTA, a higher score indicates hearing impairment.

Speech Discrimination (SD)

It is an evaluation of the ability of patients to discriminate between speech in quiet and noisy environments. The decreased score indicates a hearing loss.

Treatment for Acoustic neuroma

The treatment for Acoustic neuroma can be varied; it is usually based on the overall health of a patient, the size and the development of acoustic neuroma and its symptoms. There are three options of treatment such as observation, microsurgery, and radiosurgery (therapy).

Monitoring

• The development of slow-growing tumours at a primary level in an adult may not show symptoms, so the observation of a patient can be a significant option for further treatment.

• The size of the tumours, up to 1.5 cm is the optimum condition for a monitor. Surgery has to be done to remove the tumour before it reaches the critical size.

Surgery

• Surgery is a potential treatment of an acoustic neuroma.

• The major aim of the surgical method is to remove the tumour and prevent facial paralysis. However, in some cases, complete removal becomes impossible because the tumour may lie very close to critical parts of the brain.

• This method also includes chances of certain complications, like hearing loss, tinnitus, leakage of cerebrospinal fluid from the nasal route, facial numbness etc.

Radiation therapy

• Radiation therapy is a non-surgical treatment; most commonly stereotactic radiosurgery can terminate the growth of the tumour and reduce the destruction of the surrounding cells.

• In this method, the gamma rays are passed to the accurate tumour region without affecting adjacent cells.

• This treatment is not recommended for patients with large tumours.

Conclusion

Acoustic neuroma is a rare non-cancerous tumour that may impair hearing capacity and balance mechanism. The exact causes are unknown, but disturbances in the vestibular nerves connected to the brain and ear lead to acoustic neuroma. It has several symptoms including hearing loss, tinnitus, ear fullness, balancing issues, and dizziness. The diagnostic methods of MRI scan or CT scan and evaluation of some measurements have been used to identify the level of hearing capacity. The treatment includes observation of patients, surgery, and radiation therapy that are based on the symptoms, dimensions of the tumour, and overall health of patients.

FAQs

1. What is the importance of audiometry?

Audiometry is a diagnostic test of hearing sounds. The ability to hear sound is based on the loudness of tone and the speed of sound. It is important for the identification of hearing impairment.

2. What is stereotactic radiosurgery?

It is a type of radiotherapy. The ultimate aim of this method is to clear the tumour cells in the exact site without destroying the adjacent tissues.

3. What are the symptoms of acoustic neuroma?

The most common symptoms include,

• One-sided hearing loss

• Dizziness

• Vertigo

• Balancing issues

• Face numbness

• Headaches

4. Do all people with acoustic neuroma experience the symptoms?

No, a person with a minimum level of tumour cannot experience the symptoms of acoustic neuroma.

5. When is the surgery required to treat acoustic neuroma?

The removal of a tumour depends on the size; the growth of the tumour and the health of a patient suffering from the acoustic neuroma.

References

• Acoustic Neuroma (Vestibular Schwannoma). Hopkinsmedicine.org. (2022). Retrieved 18 May 2022, from https://www.hopkinsmedicine.org

• Acoustic Neuroma: Symptoms, Causes, Treatments, and More. WebMD. (2022). Retrieved 18 May 2022, from https://www.webmd.com

• Foley, R., Shirazi, S., Maweni, R., Walsh, K., McConn Walsh, R., Javadpour, M., & Rawluk, D. (2017). Signs and Symptoms of Acoustic Neuroma at Initial Presentation: An Exploratory Analysis. Cureus. https://doi.org/

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