What conditions can be treated
Acoustic neuroma (sometimes called vestibular schwannoma, a synonym) is a benign, usually slow growing tumour, which arises from part of the VIIIth cranial nerve, the nerve which is responsible for hearing and balance - a common symptom of this tumour is gradual hearing loss. Acoustic neuromas can occasionally occur on both sides, this feature being characteristic of patients who have the genetic condition known as Neurofibromatosis type 2 (NF 2).
Acoustic neuromas can present with the following symptoms: Hearing loss
Tinnitus (ringing in the ears)
Vertigo or balance problems
Aims of Treatment: Prevention of tumour growth (by gamma knife)
Preservation of useful hearing
Preservation of facial nerve function
Removal of tumour (by surgical excision)
Surgery was for a long time considered to be the standard treatment for these tumours. However, the operation is a very major one, and carries a small but significant risk of major complications or even death. The patient will almost certainly be completely deaf following operation, and may have weakness of the facial muscles on the affected side because of the close proximity of the facial nerve to the site of operation. In addition there is a long recovery time and the patient can expect to be off work for many weeks. It does however offer the prospect of immediate and complete removal of the tumour. Nevertheless these tumours sometimes recur following surgery, although for tumours that are too large for Gamma Knife, surgery is still the best option.
Acoustic neuromas are generally well controlled with gamma knife treatment, the usually quoted success rate being in excess of 95%. The aim is to prevent tumour growth, and this treatment is particularly well suited for tumours up to 3cm in diameter where useful hearing is still present. The risk of facial nerve damage is low, perhaps about 1%. The treatment is carried out over the course of less than a day, patients are usually back home within 24 hours (often the same day), and back at work within a few days.
AVMs (Arteriovenous Malformations)
An AVM is a collection of abnormal blood vessels consisting of one or more dilated arteries feeding into a tangled mass of smaller, fragile vessels and thence into a series of enlarged veins, before returning blood back to the heart without it having performed its normal function. They can occur at any site in the body, but are of particular concern when they appear in the brain because of the consequences of haemorrhage, which may occur if the AVM ruptures. AVMs can indicate their presence by exhibiting all or any of the following features:
- Neurological deficit
The prevention of haemorrhage is usually the main aim of treatment, and this is only guaranteed by completely obliterating or removing the AVM. The main treatment methods are outlined below.
Complete excision is a proven effective treatment. It has the advantage that with complete removal the benefits are realised immediately. The disadvantages are the relatively high risk of producing neurological impairment and, as with any surgery, the recovery time, and the risks of general anaesthesia and infection. Furthermore, because of the former consideration, some AVMs are considered to entail such a high risk of neurological damage as to be deemed inoperable.
Gamma knife has the advantage of being minimally invasive, thereby avoiding operative damage and a lengthy recovery period. It is most effective on small lesions; commonly a 90% obliteration rate (or higher) can be quoted for smaller AVMs, but this will depend on the location of the AVM within the brain. However, for larger lesions the success rate for complete obliteration decreases. A potential disadvantage of gamma knife is that a small amount of normal brain tissue directly surrounding the AVM may be at risk of radiation damage. Increasing the dose delivered to the AVM increases the chance of obliteration, but also increases the relative risk of the procedure. Careful consideration is therefore required when deciding upon dose. Obliteration of AVMs following gamma knife treatment can take up to two years (or even longer), and follow up is required during this time by means of MRI scanning at intervals. A final angiogram is then performed to confirm obliteration of the AVM.
Embolisation involves injecting resinous material, which then solidifies, into the feeing vessels of an AVM. It tends to be used for small AVMs, and alone is unlikely totally to obliterate a larger lesion. However, it may sometimes assist by reducing the size of an AVM, thereby facilitating later radiosurgery designed to 'finish off' the remainder.
Meningiomas are generally benign slow growing tumours that arise from the cells that line the brain. Very occasionally these tumours can be malignant. Meningioma is one of the commonest brain tumours, and can sometimes occur at multiple sites.
The presenting symptoms depend on the location of the tumour and are caused by the tumour pressing on surrounding tissue or nerves. Patients can present with epilepsy, but pressure related symptoms, such as headache and vomiting can also occur.
Aims of Treatment: Prevention of tumour growth (by gamma knife treatment)
Removal of tumour (by surgical excision)
Surgery aims to remove the tumour and its origin completely without damaging the surrounding brain tissue, and remains the treatment of choice for easily accessible lesions. However, if removal is for some reason incomplete, then the tumour may recur. Some tumours are so awkwardly situated as to be considered inoperable, and these tend to be those that arise from the base of the skull, where they may be intimately related to nerves, blood vessels, or other vital structures. When complete removal is not possible patients can often go on to have gamma knife treatment to any residual tumour. This is also a particularly useful treatment pathway for larger tumours, or tumours producing neurological deficits due to their sheer bulk.
Skull base lesions, and particularly those in relatively inaccessible sites such as the cavernous sinus, are particularly well suited to gamma knife treatment. Tumour control rates of up to 95% are generally quoted. Complications following gamma knife treatment, including nerve damage, have a low reported incidence - this compares favourably with surgery. Gamma knife can also be used to treat patients with multiple lesions.
Any malignant tumour may metastasise (spread) to the brain, but this is much more typical of some types of tumour than others. Malignant melanoma is the most likely to behave in this way, but other relatively common sites of origin include bronchus, breast and kidney. Metastases commonly occur in multiple sites within the brain at the same time.
Patients can present with epilepsy but symptoms occurring from focal damage or raised intracranial pressure are also common. These symptoms can include: Weakness of limbs
Tingling or numbness
Steroids sometimes have a dramatic and very rapid effect, producing clinical improvement in many patients. However, they do not destroy the tumour, but rather exert their effect by alleviating the local brain swelling that can occur in the vicinity of such a tumour. Steroids are often given in conjunction with surgery, radiotherapy or gamma knife.
Very active treatment options such as surgery and gamma knife are usually reserved for patients who have a solitary brain metastasis, or at most a fairly low number of such deposits. The primary malignancy should be well controlled, as should any other metastatic disease elsewhere in the body. For solitary lesions that lie in an easily accessible site complete excision usually provides good results, but It has been suggested that these results may be further improved when surgery is followed by radiotherapy or gamma knife. For patients with 1-3 small brain metastases and whose systemic cancer is under control, gamma knife alone is an option we would recommend. Gamma knife is ideally suited to the treatment of more than one lesion at a time (often impractical for a surgical approach), and can be repeated if necessary.
Where whole brain radiotherapy has failed and further recurrent disease is present, then gamma knife treatment can be used selectively as a boost therapy. This treatment regimen may also be considered suitable when one brain metastasis is disproportionately larger and/or more critically situated than any other.
Tumours of the pituitary arise from the anterior portion of the gland and are nearly always benign. The pituitary gland secretes a number of different hormones that control other glands in the body. Pituitary tumours (or adenomas) are described as either “functioning” or “non-functioning”, according to whether or not they are producing excessive quantities of one or another of these hormones. Functioning tumours are named after the hormone involved. The presenting symptoms are usually the result of overproduction of a particular hormone, or possibly the result of a subsequent underproduction of other hormones. The table below shows the three most common hormones involved and their presenting symptoms:
||Acromegaly: The enlargement of soft tissue, and cartilage and bones in the face, hands and feet. Can produce so-called “Gigantism”.
||Controls milk production after birth
||Prolactinoma: Features may include discharge from breasts, irregular menstrual cycle, and infertility.
||Controls cortisol production by the adrenal glands. Cortisol helps the body control blood pressure, circulation, sugar levels and stress, and many other factors.
||Cushing’s syndrome: Features include behavioural changes, face tends to be rounder, weight gain around the trunk (central obesity), bruising easily, muscle wasting and weakness,
thinning of the skin.
Other presenting features of both functioning and non-functioning tumours include symptoms related to local pressure effects, such as visual impairment from pressure on the optics nerves, and raised pressure inside the head generally.
Drugs can be used to lower abnormal levels of circulating hormones and to inhibit hormone production. This approach can cause some tumour shrinkage, particularly in the case of prolactinoma where drug treatment is usually the only method required to give excellent control of the disease.
Surgery and Radiotherapy
In most other cases management is primarily by surgery, which has a high success rate in relieving both local and hormone related symptoms. However, following surgery, there is a significant recurrence rate, and not all such tumours (especially functioning ones) can necessarily be completely removed by surgery in the first place. Post-operative radiotherapy has traditionally been used to provide further disease control, but many centres (including our own) are now beginning to report excellent results either for the use of radiosurgery as an addition to conventional radiotherapy when this latter method has also failed, or in its own right following surgery but before radiotherapy.
Gamma knife treatment is not used as primary therapy because surgery is so effective, and works more quickly to control hormone levels. Gamma Knife however, is particularly useful when treating persistent or recurrent tumours. It has been shown to be at least as effective as conventional radiotherapy in treating these recurrences, whilst reducing complications such as damage to the optic apparatus, and possibly sparing the remainder of pituitary function. Furthermore, precise calculation of the dose to vital structures such as the optic chiasm and brainstem ensures that tolerable limits are not exceeded, even where previous radiotherapy has been given as primary or secondary treatment.
Trigeminal neuralgia is a condition comprising episodes of severe pain affecting the face, in the distribution of one or more branches of the trigeminal nerve. It is characterised by attacks of short, sharp stabbing pain, which may be superimposed on a more constant ache. These attacks can last for days or even weeks. When they settle the patient may remain pain free for many months. A sensory trigger such as chewing, teeth cleaning, speaking, or touching the face in a specific place can precipitate the attacks. It is more common in patients who have multiple sclerosis, but in most patients there are no obvious associations and the cause is unknown.
There is a wide range of drugs available for the treatment of trigeminal pain of which the best known, and probably most effective, is Carbamazepine. Some patients tend to require increasing doses over a period of time, often to the point where the high doses required lead to intolerable side effects. In these patients surgical treatment methods, including radiosurgery, may be considered.
Microvascular decompression (MVD)
Microvascular decompression involves manipulation of blood vessels in the region of the root of the nerve. It is performed under general anaesthetic. This has had consistently good results, approximately 90% of patients being pain free thereafter. However, it is a major operation which carries a small but real risk of serious complications, and it does have a recurrence rate.
This technique is also performed under general anaesthetic and produces a permanent lesion of the nerve in the region of the ganglion behind the face. This usually results in pain relief in the appropriate area, and results are generally good. However complications, usually related to nerve damage, are relatively frequent.
Glycerol injections provide good pain relief with minimal sensory damage. Glycerol is injected directly into Meckel’s cave (where the branches of the nerve divide before going on to supply the face), and produces some local nerve damage. Pain control is generally good in the short term, but is often somewhat limited, and recurrence at a later stage is fairly common.
Gamma knife is becoming increasingly popular for the treatment of this condition. A fairly large dose of radiation is delivered, but to a very small and highly focussed area of the nerve. The frequency of serious complications is extremely low, though a degree of tingling and numbness in the affected area can affect up to about 10% of people undergoing this treatment. Successfully treated patients usually respond after about 2 to 6 weeks, though some will experience pain relief sooner than this. Long-term outcome studies are still needed but favourable results are beginning to emerge. Treatment is probably not quite as effective as MVD, but this is offset by the fact that the complication rate is so low, and can be delivered on a day case basis rather than requiring general anaesthesia, major surgery, and prolonged hospitalisation. Current figures suggest that about 65% of patients treated by radiosurgery will experience good or excellent pain relief.