Interest Group Acoustic Neuroma

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Acoustic neuroma operation

Skull base surgery at the highest level

A surgical operation is currently the only therapy which can completely and permanently remove an acoustic brain tumour from the body.
An open operation, and on top of that on/in your head, naturally always involves certain risks. Performed by experienced specialists, supported by a team with just as much experience and the most up-to-date technology, these risks can lessen greatly or even be eliminated, so that an acoustic neuroma operation nowadays is still the first choice.

The advances in medicine and medical technology that have been made over the last two to three decades allow for this optimistic assessment. This includes: modern diagnoses procedures and operation planning (CT and MRT), extensive preliminary examinations before the operation, highly specialised anaesthesia techniques and technology, the use of state of the art operating microscopes and increasingly endoscopes in the last few years, ultrasonic aspirators, which monitor the nerve functions during the operation, use of antibiotics pre and post operation, temporary stay in intensive and recovery rooms, and not least the specialisation of some experts in these operations, combining their high degree of experience and skills. All that rightly takes away a lot of the fear of "brain surgery".

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The cornerstones for a successful operation are already laid in the preliminary examinations and carry through to the aftercare.

One aspect warrants special attention: the thorough knowledge from the preliminary examination and the intraoperative observation allows the surgeon to vary and modify his approach during the operation – all to prevent complications and to obtain an optimal result from the operation. This is not possible with other therapies.

Preliminary examinations before an acoustic neuroma operation

There are no standardised preliminary examinations immediately before the operation to be carried out in the clinic performing the operation. In depends on the degree, quality and how up-to-date the examinations are that are carried out during the diagnosis stage, as well as on the philosophy of the surgeon. Many would simply like to have an up-to-date data, which is accrued in their clinic with technology that they know. There are also no reasons to be mistrusting with regards to old diagnosis results and also to fear that you are a particularly complicated case, and belong to a risk group because so many preliminary examinations have been arranged. The preliminary examinations serve to plan the operation and they should prevent anything unexpected complicating the course of the operation. They also offer current possibilities to compare with the post-operation status.

The following preliminary examinations may be scheduled and carried out – generally, two days before the op date:
X-ray of the throat and thoracic spine
Computer tomography (CT) and magnetic resonance tomography (MRT) of the skull,
Speech and tone audiograms and BAEP measurements (Brainstem Auditory Evoked Potential – BAEP),
Ultrasound measurements of the heart (ECG and TEE),
Blood examination.

The preliminary examinations end with information about the operation and anaesthesia. The examinations are all painless, and they pass the time and distract the patient before the operation. On request the patient may receive sedative medication or a shot the night before.

The operating procedure

An acoustic neuroma operation can be performed both by neurosurgeons and by ENT surgeons, or a team of both. The operating team may also consist of anaesthetists and doctors for intraoperative neuromonitoring.

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Operations at the highest technical level – with the operating microscope

(Sources: University Hospital Erlangen website (left) and University Hospital Jena (right))

Access to the tumour happens in different ways. Accordingly, the position of the patient is different. You can find out more about this at the end of this page. The operation always takes place under a general anaesthetic. A small area of hair shall be shaved if absolutely necessary where the skull will be opened for the operation. Before the brain is exposed for the surgeon, the thick, blood rich (outer) scalp, the cranial bone and the thick, hard (inner) meninges shall be opened. Nowadays, this is done with modern technology and with minimum dimensions. The times of large openings have passed. The miniaturisation of the technology and the operating experience make this possible. The cut through the scalp is around the length of a normal sized ear and a diamond milling cutter makes an incision through the cranial bone that is as small as a two Euro coin.

According to the operation approach, a part of the brain must be carefully pushed to the side in order to gain access either to the bony ear canal or to the tumour itself. The bony ear canal, in which generally the point of origin of the AN lies, is drilled.

The removal (resection) of the acoustic neuroma begins with an inspection of the tumour area and the course of vessels and nerves in the operation area. Predominantly this is what the operating microscope is used for. Due to the better view of structures found "further behind", endoscopes are additionally used more and more. This way even the smallest tumour remains can be detected and removed.

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Acoustic neuroma in the operating microscope (left),
the same acoustic neuroma in an endoscope (right)

(Source: University Hospital Greifswald homepage)

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Acoustic neuroma, 2x3 cm.
Left: preparation with a microscopic view.
Right: Resection with an endoscopic view (30 degree)

(Source: Clinic for neurosurgery from the University of Greifswald – » click here to visit the website)

If the surgeon gets close to or touches the nerves, this will make a sound and be recorded by the intraoperative neuromonitoring (see below) and displayed on a monitor. For one thing this provides the hoped for information about the presence of nerves and their functions, as well as letting the surgeon know that he/she is dangerously close to the nerve. In this way, the surgeon can optimise the procedure and achieve maximum protection of the nerve functions.

An acoustic neuroma is generally surrounded by a tissue capsule. This is then opened in a place where no nerve vessels are found. The numerous small blood vessels are constantly washed away and suctioned in order to have a clear view.

Only when the acoustic neuroma is still small can it be removed in one piece. In most cases, and imperatively with large tumours, it is carefully removed and suctioned piece by piece. This is essential because the abrasion of a large, heavy tumour mass would stretch the thin nerve fibres and rip them. For histological examinations small specimens are by all means taken.

Removing an acoustic neuroma from the nerve sheath is the most difficult part of the operation. This is when the individual experiences of the surgeon come into play.

An acoustic neuroma can be located on one side of the nerve wall, it can carry individual nerve fibres into the tumour capsule, however the tumour may also encase an entire nerve. It often presses both strands of the balance nerve far apart from each other, and the facial nerve is often pressed completely flat and fanned out into numerous small strands. The balance nerve, in whose sheath the AN begins to grown, is generally severed in order to be able to remove the tumour at all. The deficiencies are minor and can be later compensated for by the patients, just as the vertigo is already partially compensated for long before the operation.

One particular challenge for the surgeon is if, due to its size, the acoustic neuroma has already made contact with the cerebullum and/or the brainstem in the cranial fossa. Removing a tumour from these vital parts of the brain is particularly complex and dangerous.

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Left: Large AN, that presses on the brainstem, cerebullum and nerves, schematised.
Right: The MRT image of an AN with max. average diameter of 4.5 cm

(Sources: Homepage of University Hospital Würzburg and privately from forum member, monula)

As acoustic neuromas fundamentally begin growing from the balance nerves outwards, and due to their priority, first the facial nerves and then the auditory nerve are preserved anatomically and in terms of their function, the balance nerve is generally severed in order to be able to remove the tumour completely. With damage to the facial nerves and to prevent a later facial palsy (facial paralysis), in special cases the tumour may not be completely removed. That needs to be agreed between the patient and the doctor prior to the operation.

The space that has become free in the bony ear canal is filled with autologous fat. Subsequently, it is monitored whether the visible ways, via the cerebral ventricle fluid (liquor) from the intracranium outwards can be penetrated, or if they are too dense; if necessary they are closed with fat, muscle fibres or an "adhesive".

The operation ends with the closing of the opening in the skull. Like the opening of the skull, this is often carried out by experienced senior physicians. It is absolutely sufficient, if the opening in the bones is protected by the re-sewn, strong inner meninges and the exterior scalp. The drilled hole in the skull is closed by several surgeons with bone cement. Some surgeons reset the piece of bone and a few even screw it together.

The length of the operation is dependent on the size and location of the tumour and the skills of the surgeon. An average sized AN can be removed by an experienced surgeon in 30 to 45 minutes. However, the length of the whole operation, including the skull opening and closing, can extend from five to eight hours.

Possible complications and aftercare

The length of the in-patient stay is seven to fourteen days, determined by the post-operative dizziness. Depending on how pronounced the loss of balance due to the tumour was on entering, determines the speed of the compensation of the complete malfunction after the operation. Only patients with slight dizziness shall generally be discharged early from in-patient care.

Occasionally, clear brain fluid leaks from the wound, nose or ear. Small so-called CSF fluid leaks often stop themselves. If that doesn't occur, a so-called lumpal drainage removes the pressure in the head or/and the leak detected on an MRT is sealed with autologous matter or bone adhesive.

The hearing loss that is already present before the op often persists. If the auditory nerve is strongly affected or even damaged during the op, this leads to hearing difficulties or deafness in that ear. Losses in the hearing function can be compensated for through the appropriate hearing aids.

An irritation to the facial nerves caused by the operation can lead to a slight facial palsy (facial paralysis) which mostly disappear by themselves. However, it should also be treated with physiotherapy. Severe damages to the facial nerves may lead to paralysis that can never be completely reversed. In this case corrective subsequent operations can improve the impairments (eye closing, even position of the mouth, recovery of facial expression).

After the operation function tests will be carried out in the clinic, such as hearing and balance tests, facial nerve function tests, MRT. Depending on how the operation went and possible complaints, a follow-up appointment is agreed. Afterwards, the local doctors at the patient's place of residence assume any potential aftercare required.

The post-op patient generally requires approx. three to four weeks to recover from the operation, independently of whether he/she is taking rehabilitation measures or not. For up to one month after the operation, the patient should refrain from activities that are too strenuous physically. Water should not be applied to the op wound for two weeks or to the corresponding ear. If the facial nerve is paralysed and the eye cannot close actively, it must be masked and treated with eye drops and ointment.

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Small acoustic neuromas, intrameatal position (in the ear canal), in the vertical (left) and horizontal (right) MRT images.

(Source: Radiologic casebook website)

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Large acoustic neuromas, extrameatal position (grown outside the ear canal, into the cranial fossa), in the vertical and horizontal MRT images.

(Source: Homepage of University Hospital Tubingen)

Conclusion – Recommendations for acoustic neuroma operations

Mostly, operations remove acoustic neuromas completely (complete section).
Sometimes, however, small residues (residual tumour) are consciously left in order to save other surrounding structures, especially the brainstem, cerebullum and facial nerve. Residual tumours can grow again (relapse), therefore regular MRT monitoring is required. This makes it very clear how important early diagnosis and treatment of tumours are.

Regarding the tumour size, in terms of whether it is favourable to operate or not, there are no limits whatsoever. Acoustic neuromas of all sizes can be operated on. An operation is urgent for tumours with an average diameter of 3 cm and above.

As regards uncertain prognoses of radiation on acoustic neuromas an operation is definitely recommended for younger patients, regardless of the size of the tumour. Another reason for a prompt operation is a sense of hearing that is still intact, as defective hearing cannot be restored through an operation.

For older patients with smaller tumour and severe symptomatic vertigo, an operation likewise presents an effective treatment option, as tinnitus, vertigo and balance symptoms, which exist before the operation, mostly improve or reduce after the tumour has been removed. Although severing the balance nerve during the operation practically always leads to post-operative dizziness, this is only temporary.

An operation can be substituted by alternative radiotherapy if serious internal problems and/or the patient is of an old age and an operation would be too risky.

What are the prospects of success in statistics?

Time and again acoustic neuroma patients ask about the probability with which the abovementioned, unwanted consequences of an operation appear. This wish is understandable, however it can't be fully satisfied. Even if the statistics state, which many clinics conduct on their acoustic neuroma treatments, or the analysis of medical institutions or PhD students all correspond to the requirements of solid statistics, the individual still has many unanswered questions. There are statements about one larger or smaller average timeframe, yet the development keeps going. The statements contain averages on the different operation situations, easy to solve tumours and those "stuck together". The statement mostly don't differentiate fully the many different starting points before the operation regarding hearing ability, vertigo, tinnitus. In short, you can scarcely deduce how your own operation will go at a specific clinic based on statistics. Therefore, here we do not quote the countless existing analysis and reports on this topic, but rather solely those of Prof. Samii, the undisputedly most prestigious skull base surgeon, who has operated on acoustic neuroma since 1968 and in mid-2007 was able to look back on approx. 3000 operations:/p>

Mortality for all tumours has been far below 1%, his last 2,500 operations without a fatality.

95% retention of the facial nerves with an experienced surgeon, for tumours under 3 cm average diameter 100 % is also possible. 98,5 % of tumours out of his last 200 ANs, including ones up to 6 cm, have been completely removed.

Approximately 50% retention of hearing ability to good hearing ability and up to 70% for small tumours.

95% total resection of ANs and out of his last 200 98% were totally resectioned (average over all sizes).
Prof. Samii is the opinion that an experienced acoustic neuroma surgeon can only be called such when he/she operates on one AN per week.

In no way are we saying that statistics are worthless; quite the opposite. However, you should not procure so many domestic and statistics from abroad, but rather look at the doctor's statistics that will (potentially) operate on you. And ensure that these are from the last few years. That way you will have a good first impression of the level of the clinic and the doctor. Everything else can be gained for personal contacts and discussions.


Here you can find out more

Please read the following:
IGAN information on » The three way approach
IGAN information on » Intraoperative neuromonitoring
IGAN information on » Operation videos

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