Subarachnoid haemorrhage

Also called Brain aneurysm, Bleed on the brain

The worst headache of a life, arriving in seconds. Thunderclap headache is a 999 call, not a wait and see.

What it is

Bleeding into the space around the brain, usually from a burst aneurysm on one of its arteries.

The defining feature is the speed. A subarachnoid headache reaches maximum intensity within about a minute, usually within seconds, and people describe being hit on the back of the head. That is called a thunderclap headache and it is the single most important pattern in this entry: not how bad the headache is, but how fast it got there.

Around one in eight people die before reaching hospital, and outcomes depend heavily on getting to a specialist neurosurgical centre quickly. Rebleeding in the first days is common and often fatal, which is why the aneurysm is secured urgently by coiling or clipping.

Risk factors include high blood pressure, smoking, heavy alcohol use, polycystic kidney disease and a family history. Two or more affected first-degree relatives is a reason to discuss screening.

A CT scan very early is highly accurate; after around six hours it becomes less so, which is why a lumbar puncture is sometimes needed. Being sent home with a normal scan taken late is a known failure mode worth knowing about.

Signs you might notice

A sudden, severe headache reaching its worst within a minute. This alone is enough to call 999.

Neck stiffness and pain, sensitivity to light, nausea and vomiting.

Loss of consciousness, seizure, confusion.

Weakness, numbness, difficulty speaking, or double vision.

A drooping eyelid with a dilated pupil, which can mean an expanding aneurysm.

Sometimes preceded days or weeks earlier by a sentinel headache, a smaller sudden headache that settled. Any thunderclap headache, even a resolved one, needs assessing.

999 immediately. Do not drive the person, and do not wait to see whether painkillers help.

How it can affect day-to-day life

Survivors are frequently left with problems that do not show: fatigue that lasts a year or more, memory and concentration difficulty, irritability, emotional lability, headaches and sensitivity to noise and light.

Those invisible effects are the main reason returning to work fails, and they are routinely under-supported because the person looks recovered.

Anxiety about a recurrence is close to universal and deserves treating in its own right.

Families are often given a stark early prognosis that turns out to be wrong in either direction, and the first weeks are lived in that uncertainty.

Rehabilitation, including occupational therapy and neuropsychology, is the part most often missed.

Supporting someone well

Call 999 for any headache that reaches its worst within a minute. Say thunderclap headache.

Mention any earlier sudden headache, however brief; it changes the assessment.

Do not accept a normal CT taken more than six hours after onset as the end of the matter; ask about lumbar puncture.

Afterwards, ask for neuropsychology assessment and for fatigue management. These are the interventions that determine function.

Ask about family screening where two or more close relatives have been affected.

Control blood pressure and stop smoking; both substantially reduce the risk of another aneurysm.

Expect recovery to take a year or more, and plan a graded return to work rather than a date.

Where to get help

999 immediately for a thunderclap headache.

The neurosurgical team and the specialist nurse afterwards.

Brain and Spine Foundation run a helpline and have the clearest information on recovery.

Headway on 0808 800 2244 for the cognitive and fatigue aftermath.