The formation of an out-pouching (aneurysm) on one of the brain’s blood vessels (cerebral arteries) may represent a weak point that can lead to a brain haemorrhage at a young age. If bleeding occurs treatment to make the aneurysm safe is required to prevent a further bleed. However, most of these weak spots do not cause problems and perhaps are better understood as wear and tear features that will develop in one in ten of us through time. The difficult question is when to intervene with invasive treatment for an aneurysm that is found by chance (incidental) and will probably never cause a bleed.
The blood supply to the brain takes ¼ of the blood pumped by the heart carried by four arteries that penetrate the protective layers (skull and meninges) of the brain. The two arteries at the front are the internal carotid arteries (ICA) and the two at the back are the vertebral arteries (VA) that soon join together to form a single basilar artery (BA). These arteries are floating in a fluid-filled space around the brain (subarachnoid space) and are linked together by three communicating arteries to form an interconnecting ring of arteries called The Circle of Willis (COW). Three pairs of arteries come of this circle to supply the brain with blood. It is at these branch points on this circle that it is common for aneurysms to form and if they should bleed a potentially fatal subarachnoid haemorrhage results (SAH).
Why do aneurysm develop? Like a lot of things this is to do with a combination of our genetic makeup and our environment, or what we have put our bodies through. Some genetic conditions (Marfan’s Syndrome and Polycystic Kidneys) lead to a higher chance of aneurysm formation. Smoking, high blood pressure, high cholesterol and age increase aneurysm formation. Aneurysms must start off as a slight weakness in the blood vessel wall, just at a branch point, and further damage causes the out-pouching perhaps in an attempt to strengthen the weakness. Intracranial aneurysms are called berry aneurysms but are usually very small “fruit” like a redcurrant or the vesicles on a blackberry. Most ruptures leading to SAH probably occur at this unstable early phase because most aneurysms that bleed are small. However, once formed and stable only if they are the size of a raspberry or strawberry is treatment recommended for an incidental aneurysm.
If an SAH happens the supply of blood to the brain is cut off and if this persists for more than a few seconds the individual becomes unconscious and will die unless normal circulation is restored. In most people this would happen but ¼ will die because the blood supply does not return to normal. The patient will be aware of a sudden, severe headache that may have caused them to collapse but will normally regain full consciousness and function. If the bleed has penetrated into the brain problems with the brains function may be evident such as limb movements or speech. If there are problems with an accumulation of brain fluid (cerebrospinal fluid, CSF) water-on-the-brain (hydrocephalus) may develop to reduce the level of consciousness.
The diagnosis can usually be made from a scan but sometime an analysis of the CSF is needed via an invasive test called a lumbar puncture. The clinical severity of an SAH is graded (1-5) according to how awake the patient is and whether they have any evidence of brain damage. A patient is classified as grade 1 if they are fully awake but if in coma is grade 5. Bed rest is advised along with plenty of oral or intravenous fluid. A drug called Nimodipine is prescribed to help the cerebral circulation.
An investigation to obtain a picture of the blood vessels of the brain (cerebral angiogram) is essential but is normal in 10% of patients. This can be done with a scan but may require an invasive test with a needle in the groin (catheter angiogram).
We may all have an incidental aneurysm and not know about it. The only way to know is to have a scan of the brains blood vessels (angiogram) but do you want to know? Usually no action is required because the estimated risk of bleeding is very small and far less than the risks of treatments. Once you know others will need to be informed which may increase life and travel insurance premiums. Only if the aneurysm should be large or expanding with pressure on sensitive structures is treatment recommended. Sometimes scans are advised at 2-5years into the future to check on the situation. Lifestyle advice to stop smoking, take regular exercise and have occasional checks on blood pressure, cholesterol are advised.
The Cavernous Sinus is a large vein in the meningeal membranes behind the eye that is collecting blood from the brain and feeding it into the jugular veins in the neck. Running though the vein on the way into the subarachnoid space is one of the brains main arteries (ICA) and also nerves taking information to the muscles of the eye and sensation from the forehead. If an aneurysm forms at this point it is outside the membranes of the brain and will not cause a brain bleed but can create a swelling that can press on the nerves or rupture to create an abnormal connection between the high pressure arterial blood and the low pressure venous blood (AV fistula). Very rarely they can cause a severe nosebleed.
In 10% patients multiple aneurysm will be found on angiography. Only one of these will have bled to cause an SAH and treatment is usually targeted at the most suspicious one but the others may need treatment over time.
Angio Negative SAH
In patients with a diagnosis of SAH an investigation to obtain a picture of the blood vessels of the brain (cerebral angiogram) is essential but is normal in 10%. These patients can be reassured they do not have anything abnormal and almost zero risk of further events. It is presumed that a small vein has bled that is of no importance and the patient can be reassured.
An aneurysm can be cured from the inside or the outside both performed under a general anaesthetic. Microsurgical clipping requires the skull and meninges to be opened at a specific point, usually near to the temple, and the Neurosurgeon can then follow the CSF spaces to identify the aneurysm to place a secure titanium clip on the aneurysm. Coiling is performed from within the blood vessels with a needle in the groin accessing the leg artery and micro-catheters are then passed up the body into the brain arteries to locate and coil the aneurysm from within. Sometimes the blood vessel wall is remodelled with a stent. Both treatments are usually successful but do carry risks from haemorrhage or infection that could risk life, limbs (paralysis) or mind. Coiling may lead problems with the leg artery or even recurrence of the aneurysm over time and follow-up scans are required to ensure safety.
If you have suffered SAH then convalescence is required for 3-6 months. After discharge you still need plenty of rest, will have a headache and will not want to return to work, travel or drive until reviewed at approximately 6 weeks. If you have undergone a craniotomy your wound will need time to heal and will be swollen and sensitive for 6 weeks. If it should become red, and or discharge any fluid, then you will need to seek medical advice.