Acoustic Neuromas

An acoustic neuroma is a noncancerous growth that builds up on the eighth cranial nerve. Also known as the vestibulocochlear nerve, it joins the inner ear with the brain and has two different parts. One part is involved in transmitting sound; the other helps send balance information from the inner ear to the brain.

Acoustic Neuromas are relatively uncommon benign tumours that grow on the nerve between the brain and the inner ear. These tumours (vestibular schwannomas or acoustic neuroma) are non-malignant fibrous growths originating from the balance (vestibular) nerve. They don’t spread (metastasize) to other parts of the body. Acoustic tumors constitute 6%-10% percent of all brain tumors and are found in roughly one of every 100,000 people per year. As these tumours grow, they affect surrounding structures in the brain that control vital functions. When large (eg 4 cm or more), acoustic tumors may reason severe pressure on the brainstem and cerebellum of the brain with catastrophic consequences including stroke and death.

SYMPTOMS

The first signs or symptoms of an Acoustic Neuroma are generally related to ear function and include tinnitus (ear noise/ringing in the ear) and hearing loss on one side. You might also experience unsteadiness or loss of balance. As these tumors grow larger, they involve other surrounding nerves, for example causing numbness or pain in the face. Headache may develop as a result of enlarged pressure on the brain.

GROWTH RATE

In most cases, these tumors grow slowly over a period of years. But sometimes the rate of growth is more rapid. Symptoms can be mild or severe, and multiple symptoms might develop rather rapidly.

DIAGNOSIS

Many people have hearing loss on one side, head noises, and balance difficulties but hardly ever are these symptoms due to an acoustic tumor. A careful evaluation of everyone with these symptoms should be performed however to eliminate the occurrence of an acoustic neuroma. Today, the most common method of diagnosing an acoustic tumour is by a Magnetic Resonance Imaging (MRI) scan of the head.

In some cases, the tumour becomes relatively large before symptoms lead to investigation and diagnosis.

TREATMENT

The treatment options for an acoustic neuroma will depend on the tumour size and a variety of factors including age and hearing level. Preservation of life is the most important objective of treatment. In the modern era, very few people die from an acoustic tumor or from their treatment. The main objective of treatment is to carefully remove the tumour or control its growth whilst preserving neurologic function.

Below, three treatment options are discussed:

• watchful waiting (observation),
• surgery, and
• Radiation therapy.

The choice of treatment may be depending on tumor size, hearing in the ear at time of diagnosis, patient age and health, and, of course, patient preference.

Risks and complications of acoustic tumor treatment vary with the size of the tumor: (The larger the tumor, the more serious the complications, and the more likelihood there is of complications.)

In most cases, it’s definitely best to actively treat a great or growing tumor by surgical removal or stopping its growth with radiation treatment.

Observation

If the tumour is small at initial diagnosis, monitoring the tumor at regular intervals to be sure it isn’t growing can be an appropriate alternative. This approach is referred to as “watchful waiting” or “observation”. You must have follow-up MRI scans of the head, as often as every six months for the first year after diagnosis. If the tumor hasn’t grown, repeated MRI’s are done at the discretion of your doctor, perhaps as often as yearly. Any change in symptoms also calls for an MRI to check for tumor growth. (Because these tumors can grow rather suddenly, great care must be taken to treat the tumor before it’s so large that complications are more likely.) The smaller the tumor at time of active treatment, the better the outcome of treatment is likely to be. On the other hand, some tumors do not grow or grow only very slowly.

Associate Professor Rob Briggs, a Neurotologist and his colleagues have a big experience with acoustic tumour management. Surgical procedures to remove acoustic tumours include translabyrinthine, middle fossa, and retrosigmoid approaches. The best approach for each patient will be discussed in detail during the consultation. The choice of surgical approach depends upon the size of the tumor and amount of remaining hearing. It’s possible to save hearing in only a minority of cases; if hearing preservation is successful, the preserved hearing will not be better than the preoperative level and can be worse. The larger the tumor is, the lower the chances for hearing preservation. In some cases with poor preoperative hearing or a larger tumor, it’s better to sacrifice the hearing in order to remove the tumor.

All procedures are performed with the patient under common anesthesia. The surgeons look through an operating microscope, and special equipment is used to ‘monitor’ the facial and possibly hearing nerves to prevent injury. Surgery for these tumors, as well as the pre- and postoperative care, is performed and assisted by a team. This team includes an anesthetist, a specifically trained surgical nurse, a neurosurgeon and a neurotologist.

Stereotactic Radiation

In recent years, stereotactic radiation therapy has been used to treat acoustic tumors. This type of radiation therapy is different than radiation used for cancer. It’s highly focused on the tumor, with only low levels of radiation affecting most of the brain. This type of treatment has proved effective for certain patients with acoustic tumors. Tumors up to 3.0 cm (small or medium) have been treated with radiation. While patients of all ages can be treated, stereotactic radiation therapy is generally used only in older patients who might be poor surgical candidates or those with other medical problems that make having surgery undesirable. The long-term effectiveness of radiotherapy (20 years or more) has yet to be determined and so use in young patients is not recommended.  As with surgery, there are risks to hearing and to the facial nerve.

Hearing Preservation

In small tumors, it’s sometimes possible to save the hearing while still removing the tumor using the middle fossa or retrosig approach. When tumors are bigger, however, the hearing is generally lost in the involved ear as a result of the surgical procedure. Following the surgery in  these situations, the patient hears only with the remaining good ear. Many people function quite adequately with only one hearing ear. Alternatively there are various hearing aid options to transfer sound from the deaf side to the remaining hearing ear.