Vestibular Schwannoma (Acoustic Neuroma)

A vestibular schwannoma is commonly known as an acoustic neuroma albeit that is not technically correct. (The term acoustic neuroma has been replaced by the more accurate term vestibular schwannoma, but both remain in use).

What is a vestibular schwannoma?

• A vestibular schwannoma is a tumour (growth) that develops inside the skull on the balance nerve as it runs from the brain to ear.
• It is a benign tumour which means it is not cancer.
• The tumour grows in the sheath that covers the balance nerve, also known as the vestibulocochlear nerve.

What is the vestibulocochlear nerve?

• It is one of 12 cranial (brain) nerves and runs between the brain and the inner ear.
• All the cranial nerves come in pairs to operate both sides of the body so you have one on each side of your head.
• It is responsible for hearing and balance.

What causes a vestibular schwannoma?

• In most cases, the cause is unknown.
• Some schwannomas develop in people who have a condition called neurofibromatosis type 2.
• Vestibular schwannomas are slow-growing tumours, rarely life-threatening and do not spread to other parts of the body.
• Vestibular schwannomas grow from a type of cell called a Schwann cell which covers and insulates the nerve.

How common are vestibular schwannomas?

• Vestibular schwannomas are rare.
• In the UK, 13 people in every million are diagnosed each year with a vestibular schwannoma.
• They are generally more commonly diagnosed in people aged 30 to 60 and extremely rare in children.
• They tend to be more common in women than men.

What are the symptoms?

Vestibular schwannomas are very slow-growing and may even stop growing spontaneously and remain very small, causing no symptoms whatsoever. As they are slow-growing tumours, the symptoms often also develop slowly over time and may not be obvious at first. Symptoms caused by vestibular schwannomas are common to many other illnesses and conditions. The symptoms that a vestibular schwannoma can cause are very common in the general population. Remember that vestibular schwannomas are very rare. You should see your doctor if you have any of these symptoms, but they are more likely to be due to other conditions.

• Gradual hearing loss in one ear.
• Tinnitus: This is commonly referred to as ringing in the ears. However the type of sound is not necessarily a high-pitched ring. It is a sound within the ear for which there is no external cause.
• Vertigo: This word describes dizziness or a spinning feeling even though you are standing still.

Other symptoms can arise if the tumour is causing pressure on other nerves which lie close to the balance nerve. Commonly the trigeminal nerve (the largest of the cranial nerves, responsible for sensation in the face) is involved and can result in the following:

• Facial numbness
• Facial pain
• Tingling

In very rare cases and usually if a tumour has become quite large, the following symptoms may be experienced:

• Facial weakness or twitching
• Headache
• Earache
• Fatigue

If the tumour is very large a condition called ‘hydrocephalus’ (water on the brain) can develop. In a healthy brain, there is fluid which circulates through and around the brain called cerebrospinal fluid (CSF). The drainage channels for the fluid become blocked because the tumour squeezes the brain and the drainage channels are very narrow.  When the drainage system becomes blocked, fluid accumulates in spaces within the brain called ventricles.  As these expand with fluid, the brain is squeezed against the inside of the skull. This can cause a range of symptoms (for example: severe headache often worse in the morning and exacerbated by coughing or straining, confusion, visual disturbances, dizziness, drowsiness and in extreme circumstances, reduced consciousness).

How is a vestibular schwannoma diagnosed?

A vestibular schwannoma is often difficult to diagnose because they can be very small indeed and give very few – if any – mild symptoms. Many other conditions can cause similar symptoms.

• If your GP suspects a vestibular schwannoma, then you will be referred for a hearing test.
• At the same time your GP may refer you to an ENT (ear, nose and throat) specialist, especially if you have developed nerve-related hearing loss (sensorineural hearing loss).
• Magnetic resonance imaging (MRI) of the brain is the most accurate diagnostic test for vestibular schwannoma. A strong magnetic field and radio waves give detailed pictures of the structures in your brain. It is a painless test but the scanner can be noisy.
• MRI with contrast may also be used. Contrast refers to a dye which is injected into a vein to show up details of the smaller brain structures, and reveals even tiny tumours.

What is the treatment for a vestibular schwannoma?

If the tumour is small, the doctors may just monitor the tumour by arranging regular scans. It is safe to do this as vestibular schwannomas grow slowly or not at all and may remain very small even after many years. Removal of tumours can carry certain risks so the benefits must be greater than the risks.

If the decision has been to observe and monitor, you will require regular scans initially every six to twelve months depending on individual circumstances. This allows regular measurements to assess tumour growth. People who are most likely to be offered a monitoring programme are:

• The elderly
• Those with small tumours, especially if hearing is good
• Those with medical conditions and increased risk with operation
• People who refuse treatment
• People who only have hearing in that ear

The main treatment options are as follows:

• Surgery
• Radiotherapy (also called Radiosurgery)

The type of treatment offered will depend on your age and your general health.  It will also depend on the size and position of the tumour. There are a number of other factors that may influence the best choice for you and the doctor will consider all of these with you so that you make the most appropriate choice.

Surgery

Surgery is carried out to remove the tumour under general anaesthetic, by a neurosurgeon (brain surgeon) and an ENT surgeon. The majority of tumours can be removed completely,but the surgeons will occasionally leave a small amount of tumour if removing it would cause permanent damage. Small amounts of tumour left in this way generally do not grow or need further treatment.

• You will need to stay in hospital for a few days
• Full recovery takes place within six to twelve weeks
• Your follow-up appointments will be scheduled as necessary by your surgeons, and an MRI will be obtained a few months after surgery to ensure that tumour removal is complete. This MRI will also provide a baseline for future scans which may be prudent.
• Report any post-operative concerns to your GP and at your follow-up appointments with your hospital consultant.

What are the risks of surgery?

The risks of surgery will be explained to you by your surgeon. Each case is individual, and for some people the risks will be low and for others the risks will be greater. These will be discussed with you in detail before you agree to go ahead with treatment. Listed below are some of the possible risks.

• Hearing loss on the side of the tumour
• Facial weakness due to damage to the facial nerve. The facial nerve is very easily damaged because it is so tiny and often stretched over the tumour. Bruising, stretching or disturbance to the facial nerve may cause a facial weakness also known as a facial palsy.
• In very rare cases, usually when the tumour is large and has been difficult to remove, a permanent facial paralysis will result. There are various surgical procedures available to restore some movements such as eye closure and smile.
• Loss of sensation or numbness of the face on the side of the tumour
• Meningitis
• Leakage of cerebro-spinal fluid from the incision, ear or nose. This often stops spontaneously but may need further surgical intervention before you can be discharged.
• Stroke

Radiotherapy

• Stereotactic radiosurgery, GammaKnife and CyberKnife: These techniques require very specialised equipment, which may mean travelling to a specialised centre for treatment. This method of therapy delivers a single high dose of radiation to the tumour. No surgical incision is made but a head frame or mask is used to keep the head still to precisely locate the tumour. Once located, a treatment plan is made and the radiation dose delivered. Treatment does not require a hospital stay, only a day case admission
• Radiation therapy is used to treat small and medium-sized vestibular schwannomas and the goal is to stop the growth of the tumour. This treatment works by delivering controlled high-energy rays of radiation to the tumour: the aim is to damage the cells so that they are unable to divide and reproduce.
• The results are not immediate but develop gradually over time as the tumour stops growing or shrinks in size.
• It does not remove the tumour and therefore periodic MRI scans are required throughout the patient’s lifetime to monitor any changes.

The radiation machines

Two types of radiation machinery are mainly used for this type of tumour: Gamma Knife and Cyber Knife.

• The Gamma Knife resembles a helmet that surrounds the patients head; it uses 201 individual beams of radiation that are targeted into the tumour. Each beam travels through a different area of the brain, intersecting at the tumour site and causing the necessary damage to stop the tumours growth.
• The Cyber Knife uses a linear accelerator to produce radiation that is referred to as high energy X-ray. The machine is mounted on a robot arm allowing it to fire multiple pencil beams of radiation which converge on the tumour, minimising radiation exposure to healthy tissue while killing tumour cells.

What are the chances of your vestibular schwannoma recurring?

• The chances of your vestibular schwannoma coming back (recurring) are very low: fewer than five in every 100 cases of vestibular schwannoma experience recurrence.
• Those at higher risk of recurrence are people diagnosed with Neurofibromatosis type 2 with tumours on both sides.
• You will be followed up by your consultant at regular intervals as discussed with your doctor.