Subarachnoid haemorrhage (SAH) affects a person suddenly and usually without any prior warning.
It is a leakage of blood beneath the arachnoid membrane of the brain (pictured opposite) from a major blood vessel.
SAH causes the sufferer to develop sudden and severe headache, which is often accompanied by nausea, vomiting, neck stiffness and sometimes collapse, seizure and loss of consciousness.
What causes a Sub-Arachnoid Haemorrhage?
In approximately 75% of cases, leakage of blood occurs from a weak spot in the wall of an artery at the base of the brain that bulges outwards to form an aneurysm. This leakage of blood lasts only for a few moments and then stops spontaneously as a rule. The reasons why aneurysms develop is not fully understood but we do know that aneurysms are a relatively common finding and occur in approximately 2-4% of the population and are not usually associated with symptoms.
Approximately 20% of patients have more than one aneurysm. Ruptured aneurysms pose a much greater risk than those that have not ruptured, so there is no urgency to treat an aneurysm that has not bled. Indeed, it is not always wise to treat this kind of aneurysm. The issue will usually be discussed with you at your follow up appointment. Rupture of an aneurysm is unusual and the risk of rupture is increased by smoking, high blood pressure and excess alcohol. Once an aneurysm has bled, there is a high risk of re-bleed in the short term and so it is important to block off the aneurysm so it cannot bleed again. This is done either from within the aneurysm using special coils or by closing the neck of the aneurysm using a surgical clip during an operation.
No Vascular Abnormality Found
In approximately 15% of cases there is no vascular abnormality that is identified on cerebral angiography, which could have caused the sub-arachnoid haemorrhage. It is not known why such haemorrhages occur, but we do know that prognosis or outlook is good, and the risk of you having a future sub-arachnoid haemorrhage is very low. As no abnormality which could have caused the haemorrhage has been identified, there is no area that requires treatment, and therefore no neurosurgical or radiological intervention is necessary. This is a good result, and it is likely that whatever caused the bleed has subsequently healed itself in the process. You may go on to have a further angiogram, or MRI Scan, in order to confirm the absence of any cause. Despite the fact that intervention is not required, you will still need to allow yourself time to recover from the sub-arachnoid haemorrhage itself.
Arterio-Venous Malformation (AVM)
An arterio-venous malformation (AVM) is the cause of sub-arachnoid haemorrhage in approximately 5% of cases. An AVM is an abnormality of the vascular network, whereby arteries and veins develop in a haphazard manner, often forming a knot-like appearance of vessels. An AVM will have been present from birth. The irregular formation of the vessels gives rise to weaknesses, which can result in haemorrhage. An AVM is an area of weakness of the vessels, and there is a risk that you might have another haemorrhage in the future if it is not treated. The treatment of AVMs will depend on many factors including the size, position and exact blood vessels that are involved. The chance of another bleed from an AVM is less than from an aneurysm, and this will influence treatment options. The treatment of an AVM is very individualised and the consultant will discuss the most suitable plan with each person, but it may involve a combination of surgical and radiological procedures and sometimes a special form of radiotherapy, although it must be emphasized that AVMs are not tumours.
There are other less common causes of spontaneous sub-arachnoid haemorrhage which can include bleeding from a tumour or problems with blood clotting.
Each case is considered individually and can be dependent upon many factors. The best treatment option is decided in a discussion between clinical staff (surgeon and radiologist) and this is then discussed further with the patient and/or family. Any treatment method carried out on the blood vessels of the brain carries the risk of serious complications including stroke and death. Treatment is only considered if the benefits of the treatment are greater than the risks of the treatment to the patient.
Whilst in hospital, the aim is to promote rest, and control any pain and nausea. Close observation will be necessary of signs such as blood pressure and neurological state. The aim of treatment will be to reduce the chances of another haemorrhage occurring from the same site in the future.
How are aneurysms treated?
There are two main types of treatment available, surgical clipping or coil embolisation. The treatment offered will depend on many factors, including the position and shape of the aneurysm, and will be carried out at a time that is considered best in each individual situation. An operation may be delayed if the doctors feel that the person is too unwell, as this can increase the risks of the surgery.
This involves an operation under general anaesthetic, and is carried out by a Neurosurgeon. A section of the hair may be shaved (commonly at the front), and then a cut will be made in the scalp. A piece of bone will be removed in order to allow the surgeon access to the brain. Once the surgeon has found the aneurysm a metal clip is placed across its neck to seal it off, and prevent the risk of a further bleed from it. The piece of bone is then replaced, and the scalp stitched or clipped (stapled) together again. A large bandage may be placed on the head.
This is the traditional treatment approach but a recent study has shown that the same result can be achieved with the non-invasive procedure of coiling.
During endovascular treatment, the aneurysm is packed with small platinum coils. With the patient under general anaesthetic, a small catheter is introduced at the groin into the major artery and navigated, using x-ray screening into the aneurysm. In this way, coils can then be deposited inside the aneurysm. The aim is to pack the aneurysm with coils so that blood is then unable to enter it. The diagram shows this technique. This procedure was originally developed to treat aneurysms not accessible by surgery and was first performed in the UK in 1992. Occasionally other materials other than coils may be used. The long-term benefits of coiling have yet to be confirmed but it is expected that the benefits will be long lasting. There is usually a follow up scan or angiogram carried out at six months following this treatment method.
Some people have an aneurysm that ruptured to cause SAH but it was left untreated. This is usually because the risks to the patient of treatment were greater than the risk if nothing were done. After six months, the risk of another haemorrhage from a previously ruptured but untreated aneurysm is small. In this case, it is advisable to stop smoking, drink alcohol only in moderation and ensure that blood pressure is kept within normal limits.