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What is Acoustic Neuroma: Symptoms, Causes, Diagnosis, and Treatment

Definition and Overview

Acoustic neuroma is a non-cancerous tumour that grows on the Schwann cells found in the myelin sheath of the vestibulocochlear nerve; the nerve that connects the inner ear to the brain.

In the United States, around three thousand new cases of acoustic neuroma are diagnosed every year, mainly due to recent developments in medical imaging such as MRI scan. Most of the patients diagnosed with this condition are aged between thirty to sixty years old.

Slow to develop and relatively rare, acoustic neuroma affects the patient’s hearing and balance. There are some cases, however, in which the benign tumour grows much faster, affecting other important functions of the brain.

The rise in acoustic neuroma diagnoses is credited to improved medical imaging technologies, which can detect even small tumours that were previously unseen. Auditory tests to assess the listening and comprehension levels of the patient can be the first step towards diagnosis, as the doctor will be looking for reasons why hearing is impaired. In most hospitals and clinics, an MRI scan that uses gadolinium as contrasting agent is the most preferred equipment for diagnosing acoustic neuroma.

Cause of Condition

In some cases of acoustic neuroma, the cause is not easily identified; some medical professionals diagnose their patients with this condition and attribute it to idiopathic conditions. Research shows that a defect in the suppressor genes, mainly the ones in the chromosome 22 typically causes the condition. In normal individuals, the gene in chromosome 22 produces proteins that are responsible for controlling the production and development of the Schwann cells in the vestibulocochlear nerve’s myelin sheath. Without this protein, the Schwann cells’ growth can go haywire and cause a tumour to grow right on the covering of the nerve. However, what research does not show is the reason why the gene does not function properly.

There are some studies that discovered the faulty gene is inherited, and usually comes with another disorder called neurofibromatosis type 2. This disorder involves tumour growth on nerves that are responsible for achieving balance on both sides of the head. Neurofibromatosis can cause complete deafness when left undiagnosed and untreated.

However, around 90% of acoustic neuroma cases form spontaneously, without a history of neurofibromatosis type 2 in the family. Though complete deafness is not usually observed or reported by patients, it is best to undergo treatment right after diagnosis to prevent serious complications such as severe hearing impairment or total loss of balance.

Key Symptoms

In many cases of acoustic neuroma, the tumour grows progressively over time, at the rate of one to two millimetres ever year. When the tumour expands, it takes the place of normal brain tissue, causing impairment in normal, life-sustaining brain functions. The tumour does not invade the brain but pushes and displaces brain tissue as it grows. This places serious pressure in the brain, the cerebellum and the brain stem.

Most of the early symptoms of these tumours are mistaken for those of other conditions, or as part of the normal ageing process. Some patients have been told that earlier exposure to noise is the cause of the symptoms they are experiencing. Many doctors in the past failed to diagnose earlier stages of acoustic neuroma because of the symptoms it shares with other conditions.

In 90% of acoustic neuroma cases, the first symptom is reduced hearing in one of the ears, known as unilateral hearing loss. As the tumour grows, hearing loss grows worse. This symptom is usually accompanied by tinnitus, or a ringing sound consistently heard by the patient when no such sound exists externally. Tinnitus can be present with or without acoustic neuroma.

Patients suffering from this condition can also experience dizziness and difficulty with balance. In some cases, unstable balance might occur from time to time and is typically relatively mild. Many patients report that walking in the dark can be a tough challenge with acoustic neuroma. They also have an impaired perception of stability, which can cause dizziness and impaired function of the proprioceptors in the brain.

Many patients also experience headaches, before and after the treatment of their condition. Facial pain can also be a symptom, especially since the tumour typically affects the nerves in the brain that control the movement of facial muscles.

Who to See and Types of Treatments Available

Treatment for this condition varies and depends on the tumour’s size and progress of growth. General practitioners or family doctors typically present three general treatment options for acoustic neuroma, namely: monitoring, surgical removal, and radiation therapy.

Monitoring involves careful observation over a certain period. This option is for cases wherein the condition is slow to develop and the tumours are benign, so many doctors recommend monitoring the progress of the tumours instead of aggressively treating them. It is important to note, however, that monitoring is an ideal option when the symptoms are not serious or life-threatening.

Surgery can take multiple approaches, including the middle fossa, retrosigmoid or sub-occipital, and translabyrinthine. Each patient will be carefully evaluated in terms of the location and size of the tumour, the goal of the procedure (such as preservation of hearing or removing excess pressure in the brain stem), and the experience and skill of the surgeon performing the procedure. Microsurgery can also be an option to partially or totally remove the tumours.

Radiation therapy, on the other hand, involves the use of small radiation waves directed at the tumour, without significant damage to the surrounding brain tissue. Research shows that radiotherapy results in higher success rates compared to surgery in removing the tumour, and preserving hearing in patients.

References:

  • Baloh RW, Jen J. Hearing and equilibrium. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 430.

  • Brackmann DE, Arriaga MA. Neoplasms of the posterior fossa. In: Cummings CW, Flint PW, Haughey BH, et al, eds. Otolaryngology: Head & Neck Surgery. 5th ed. Philadelphia, PA: Mosby Elsevier; 2010:chap 177.

  • Battista RA. Gamma knife radiosurgery for vestibular schwannoma. Otolaryngol Clin North Am. 2009;42:635-654.

  • Sweeney P, Yajnik S, Hartsell W, Bovis G, Venkatesan J. Stereotactic radiotherapy for vestibular schwannoma. Otolaryngol Clin North Am. 2009;42:655-663.

  • Conley GS, Hirsch BE. Stereotactic radiation treatment of vestibular schwannoma: indications, limitations, and outcomes. Curr Opin Otolaryngol Head Neck Surg. 2010 Oct;18(5):351-6.