Acoustic Neuromas:

(also known as vestibular Schwannomas)

This page is intended as a patient/relative information source only. It is not a substitute for professional medical advice.

What Is An Acoustic Neuroma?

Acoustic Neuromas or Vestibular Schwannomas are benign tumours that account for less than 10% of brain tumours. They are the most common tumour to arise from the cerebello-pontine angle (the junction between the cerebellum and the pons, which houses a wide variety of important neurological structures, including cranial nerves (nerves that control the face, mouth, eyes and ears), arteries and veins).

Cranial nerves are each given numbers, which range from 1 to 12 on each side. The 8th nerve (known as the vestibulo-cochlear nerve) is the origin of an Acoustic Neuroma. This nerve is involved with the function of hearing and balance. In particular, tumours arise from the Schwann cells that line the vestibulo-cochlear nerve, hence the alternative name Vestibular Schwannoma.

What Causes Acoustic Neuromas?

The majority (95%) of Acoustic Neuromas form spontaneously, but a small percentage are associated with a hereditary condition known as Neurofibromatosis type 2 (2).

How Does An Acoustic Neuroma Present?

The number of Acoustic Neuromas diagnosed is increasing. This is probably not due to a true increase in the number of tumours but more likely to be due to improved diagnostic technology and the fact that more people are having head scans these days.

The majority of Acoustic Neuromas do not cause any symptoms and the tumour may be found by chance during other investigations. If symptoms are present, the clinical signs depend on the size of the tumour and the neurological structures to which it is impeding. Hearing loss on one side is the most common presenting complaint and this can be associated with tinnitus (ringing in the ear), facial muscle weakness, a loss of sensation to the face and balance abnormalities. In a large tumour the presentation can include signs of raised intra-cranial pressure such as nausea, vomiting, early morning headaches and loss of consciousness (3).

The majority of patients present with symptoms between the ages of 40 and 60, although those with Neurofibromatosis type 2 often present in their 20s. Another difference between the two types is that patients with Neurofibromatosis type 2 often have Acoustic Neuromas on both sides of their brain leading to symptoms in a symmetrical pattern.

How is an Acoustic Neuroma Diagnosed?

Any patient presenting with hearing loss on one side should be investigated for an Acoustic Neuroma. This will begin with a detailed history, taking account of the presenting complaint, past medical history, medication history, social history and family history. This will then be followed by a physical neurological examination that will pay particular attention to the function of the hearing, balance and facial muscle function. The hearing level will be classified as this can affect the choice of treatment.

The diagnosis of an Acoustic Neuroma is usually made by performing an MRI scan.

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The MRI scan will be used to assess the size and position of the tumour as this will then help to decide on the most suitable management plan.

How Are Acoustic Neuromas Treated?

There are three options for the management of Acoustic Neuromas. Management decisions involve a team of professionals from both neurosurgery and ear nose and throat surgery.

The clinical decision to make with Acoustic Neuromas is whether to actively intervene or closely monitor at any early stage, as some tumours may never grow enough to cause symptoms.

In general, a “Watch and wait” approach which tends to be preferred for patients with small acoustic neuromas, elderly patients with other co-morbidities and those who decline active intervention. The process requires the patient to return to the clinic regularly for an MRI scan and clinical assessment with the aim of active intervention only if any significant changes appear.

Radio-surgery is a non-invasive active intervention that uses a machine known as the Gamma Knife to administer focussed radiotherapy to the tumour under the guidance of MRI imaging. The aim is not to remove the tumour but to halt further growth and therefore prevent the progression of symptoms. As the tumour is not removed, follow-up MRI scans will be performed to monitor the tumour characteristics. The patient is usually awake for this procedure.

Surgery is the final treatment option and can be performed via three different techniques; the trans-labyrinthine, middle fossa and retro-sigmoid approaches. All three techniques have different approaches to the tumour however share the same goal; removing as much of the tumour as possible while preserving neurological function. The choice of technique depends on the position of the tumour, the size of the tumour and the hearing status of the patient. Generally, if the pre-operative hearing is poor then the trans-labyrinthine approach will be used, whereas if hearing preservation is a post-operative goal the decision as to whether middle fossa or retro-sigmoid surgery is chosen will depend on the tumour size and position as well as patient choice. The patient is given a general anaesthetic before surgery and so will be asleep for the procedure (4). After this type of surgery, patients will typically be managed on a high dependency unit, at least for the first night after surgery, so that they can be closely monitored.

What Is The Outlook?

As Acoustic Neuromas are benign the prognosis is very good. There may be complications following surgery however and these could include a degree of hearing loss and facial muscle weakness on one side.

Current research is looking into the management of Acoustic Neuromas and whether treating patients with small tumours early with the Gamma Knife is more beneficial in the long term than watchful waiting followed by active intervention.

Furthermore, new studies are being undertaken to develop new surgical approaches to the cerebello-pontine angle in order to aid tumour removal and minimise post-operative complications (5).

In order to improve the support system for those with brain tumours, we have specialist oncology nurses who work closely with the medial staff and patients to help in every way that we can. For further information click here.

Brain Tumour Research and Support (External Website):
Brain Tumour Research and Support is a Yorkshire-based brain tumour charity, providing funds for brain tumour research and patient support. The link below leads to their website, which offers lots of information and support for patients and families of people with brain tumours.

References:

Brackmann, DE and Arriaga, MA (1993). ‘Differential diagnosis of neoplasms of the posterior fossa’ in Otolaryngology and Head and Neck Surgery. Cummings, C.W. and Harker, L.A. Editor. St Louis, MO: Mosby Year Book Inc. 3271-91.
Scherer, S & Gutmann, D (1996). Expression of the neurofibromatosis 2 tumor suppressor gene product, merlin, in Schwann cells. Journal Neuroscience Research, 46, 595–605.
Selesnick, SH, Jackler, RK & Pitts, LW (1993). The changing clinical presentation of acoustic tumors in the MRI era. The Laryngoscope, 103(4), 431-6.
Wiet, RJ (2006). Ear and Temporal Bone Surgery, Minimising risks and complications. Thieme
Sampath, R, Glenn, C, Patil, S, Vannemreddy, P, Gardner, L, Nanda, A & Guthikonda, B (2012). A Novel Method of Identifying the Internal Acoustic Canal in the Middle Fossa Approach in a Cadaveric Study—The Rule of 2s. Journal of Neurological Surgery Part B Skull Base, 73(4), 253-260

Page Author: Mr Benjamin Wood, November 2014