Subarachnoid haemorrhage (ruptured aneurysm)

A subarachnoid haemorrhage is bleeding into the narrow space between the brain and its coverings, where normally there is nothing but cerebrospinal fluid. The cause is almost always the same: an aneurysm has burst — a bulge on the wall of an artery in the brain that the person knew nothing about until that minute. It is one of those conditions where the outcome is decided less by how well it is treated than by how quickly someone reaches hospital. So this page starts not with anatomy but with the sign it exists for.

The headache that is at its worst within seconds

A sudden headache, the worst of a person's life, that builds not over hours but over seconds. People describe it as a blow to the back of the head, an explosion, or as though something burst inside the skull. The key feature is not that the pain is severe but that it is instantaneous: less than a minute separates "I was fine" from "I cannot bear this". An ordinary headache does not behave like that; it comes on gradually.

Often, though not always, something else comes with it:

• vomiting, frequently without any nausea beforehand;
• ordinary light becoming unbearable, with a need to shut the eyes and turn away;
• pain and stiffness in the neck, being unable to bring the chin to the chest;
• loss of consciousness, from a few seconds to prolonged;
• a seizure;
• confusion, agitation, odd behaviour, drowsiness;
• double vision, a drooping eyelid, weakness or numbness down one side, disturbed speech.

It often begins during straining, a bout of coughing, lifting something heavy, sex or a sudden effort — but just as often it starts at complete rest, so the absence of any exertion rules nothing out.

With a headache like that, call an ambulance immediately: across Europe the single emergency number is 112. Do not wait to see whether a painkiller works, do not stop to take a blood pressure reading, and do not weigh up whether it is worth bothering the doctors. A sudden headache that peaks within seconds is an emergency call, and there is no other correct response.

Even if the pain has eased, that is not the all-clear

The commonest and most costly mistake looks like this: the pain doubles someone over, they take a tablet, lie down for an hour or two, feel better, and conclude that it was nothing. Sometimes several entirely normal days follow.

The reason this matters is that an aneurysm can produce a small, contained bleed, known as a warning or sentinel bleed. It shows itself as exactly the same sudden, explosive headache, only less severe and shorter-lived; sometimes neck pain, dislike of light and vomiting come with it, and sometimes there is nothing but the pain. Over hours or days it all fades. And then, days or weeks later, the major rupture happens in the same place, and that one is deadly.

Hence a rule worth memorising word for word: a sudden, extremely severe headache needs investigating even once it has completely gone. The sentinel bleed is the window in which the aneurysm can still be found and sealed before the catastrophe, and it is offered once. If that headache was yesterday and today you feel fine, that is not a reason to cancel the appointment; it is a reason to be seen today.

What to do while the ambulance is on its way

• Tell the call handler exactly this: a sudden, extremely severe headache that reached its peak within seconds, and give the time it started. That changes both the priority of the response and the destination: what is needed is a hospital with round-the-clock scanning and neurosurgery.
• Lay the person down with the head end slightly raised, dim the lights and the noise, do not shake them and do not get them onto their feet.
• Do not give aspirin or any other medicine that thins the blood: in a bleed they make the bleeding worse.
• Give nothing to eat or drink: urgent anaesthesia may be needed, and with impaired consciousness it is easy to choke.
• If they are unconscious but breathing, turn them onto their side. If a seizure starts, move dangerous objects away, put something soft under the head, and do not try to force the mouth open or hold the limbs still.
• Do not get behind the wheel yourself, and do not let the person go anywhere alone: consciousness can go at any moment.
• Note and write down what time the pain started, what they were doing at that moment, what medicines they take, and whether there have been similar episodes before.

How it is diagnosed, and why a clear scan is not always the end of it

The first test is a scan of the head without contrast. Fresh blood in the subarachnoid space shows up well, and in the first hours after a rupture this test picks up the overwhelming majority of haemorrhages. If blood is visible, imaging of the vessels with contrast follows straight away, to find the aneurysm itself and decide how to seal it.

The difficulty lies elsewhere. The sensitivity of the scan falls with every hour and every day that passes: the blood gradually breaks down, and after a few days the image can come back entirely clear even though there was a haemorrhage. That is why "there's nothing on the scan" does not on its own rule out the diagnosis — and yet it is far too often taken as a final all-clear, and people go home on the strength of it.

If the picture is typical and the scan showed nothing, the next step is a lumbar puncture: a needle in the lower back draws off a little cerebrospinal fluid, which is examined for blood and for the products of its breakdown. It is not done immediately but some hours after the pain began, because before that those breakdown products have not yet appeared. The procedure is unpleasant but tolerable, and it is what settles the question where the scan was inconclusive. Sometimes imaging of the vessels with contrast is used instead or alongside it. The principle is the same either way: with a typical sudden headache the work-up is carried through to the end and does not stop at the first negative result.

Where it comes from and who it happens to

In the great majority of cases the cause is a ruptured aneurysm. An aneurysm is a bulge in the wall of an artery at a point where the wall is weaker; it grows over years and usually gives no sign of itself, so it is found either by chance on a scan done for another reason or after it has already burst. Most aneurysms never rupture at all.

Less often the bleeding has other causes: a severe head injury, a congenital tangle of abnormally formed vessels, inflammation or dissection of an artery wall, clotting disorders and medicines that thin the blood, and the use of cocaine and amphetamines.

What genuinely raises the risk of rupture:

• Smoking. The heaviest modifiable factor by far, and stopping lowers the risk appreciably.
• High blood pressure, particularly when untreated.
• Cases in the family. If two or more close relatives have had a subarachnoid haemorrhage or a ruptured aneurysm, it is worth discussing scanning of the brain's blood vessels with a doctor.
• Polycystic kidney disease, an inherited condition in which brain aneurysms are markedly more common; the same applies to some inherited disorders of connective tissue.
• Heavy drinking; being female; the age band between forty and sixty, although it also happens far earlier.

What is done in hospital

The first task is to seal the aneurysm, because left untreated it can rupture again within days, and a second rupture is tolerated far worse than the first. This is done in one of two ways. A catheter is passed through a puncture in an artery up to the aneurysm and the sac is packed from within with fine metal coils, sometimes supported by a stent; this is the endovascular route and it does not involve opening the skull. Or an open operation is performed and a clip is placed across the neck of the aneurysm. Which suits depends on the shape of the aneurysm, where it sits and the state of the person, and the neurosurgical team decides.

Alongside that, the complications of the first fortnight are managed, and there are several. The brain's arteries may go into spasm and narrow in response to blood around them, which risks a stroke; a medicine from the calcium channel blocker group is given against this and the person is watched closely. Drainage of cerebrospinal fluid can be obstructed and hydrocephalus develop, in which case the fluid is drained off, sometimes temporarily and sometimes permanently. Blood pressure, the sodium level in the blood, pain and the risk of seizures are all kept under control. The first days are usually spent in intensive care, and that is what is expected rather than a sign that things are hopeless.

Life afterwards

Outcomes vary enormously, and they depend above all on how much blood was spilt and how quickly the person reached the neurosurgeons. Some people return completely to the life they had. Others are left with consequences, from barely noticeable to severe.

What people most often meet is not paralysis but the things that do not show from the outside: a heavy fatigue that was not there before, headaches, trouble with memory and concentration, slowness of thought, irritability, anxiety and low mood, poor tolerance of noise and crowds. This is a direct consequence of the haemorrhage rather than someone letting themselves go, and the family needs to know it: it is precisely the lack of understanding around them that makes recovery so hard. Less often there is weakness in a limb, disturbed speech, changes in vision or in the sense of smell, and some people go on to develop epilepsy.

Recovery takes months and sometimes years, and noticeable improvement is still possible a year after the event. A physiotherapist, a speech and language therapist, an occupational therapist and a psychologist all have a part in it. After that come follow-up, repeat imaging of the vessels, treatment of blood pressure and, above all, stopping smoking completely — the single most effective thing a person can do for themselves to avoid ending up here again. Returning to driving, to work and to physical exertion is decided individually and without hurry.

Online consultation

The acute situation is not for a remote appointment: a sudden, extremely severe headache needs an ambulance, and this is not the moment to message a doctor and wait for a reply. But a remote consultation has three clear uses here. The first is making sense of an episode that has already passed: the doctor will ask exactly how the pain began and say whether it calls for urgent assessment in person — and very often it is that conversation that gets someone seen in time. The second is family risk and an aneurysm found by chance: what the report means, whether follow-up is needed and how often, and which relatives it makes sense to investigate. The third is support after discharge: going through the prescriptions and the timing of follow-up scans, discussing the fatigue, the headaches and the low mood, helping to plan a return to exertion, and explaining to the family what they are dealing with.

This material is for information only and does not replace medical advice.