Your next patient has a sudden headache with vomiting that began 2 hours ago. Here's how the subarachnoid haemorrhage case unfolds and what to pick up on the way.

Here is a subarachnoid haemorrhage case that is easy to get wrong if you focus on vomiting or photophobia and label it a primary headache, or if you miss brief loss of consciousness, exertional thunderclap onset, or a short warning leak days earlier. The headache is sudden, maximal within seconds on exertion, often occipital, and the patient may call it the worst of their life, with neck stiffness, photophobia and vomiting, sometimes with a brief blackout.

This page walks through how the case presents, what to pick up in the history, the tests and the teaching points. You’ll see why asking about a preceding sentinel headache matters, and how risk factors such as smoking, hypertension, family history and polycystic kidney disease should steer your suspicion.

How the case presents

Your next patient has a sudden headache with vomiting that began 2 hours ago. In their own words: "The worst headache of my life came on suddenly a couple of hours ago, with vomiting."

Observations on arrival:

Observation	On arrival
Heart rate	88 beats per minute
Blood pressure	182/102 mmHg
Respiratory rate	18 breaths per minute
Oxygen saturation	98%
Temperature	37 °C

What to pick up in the history

These are the findings the case is built around. Each one moves you towards or away from subarachnoid haemorrhage, and the scorecard checks whether you found it.

Thunderclap onset, maximal within seconds on exertion: maximal-in-seconds onset is the defining feature of subarachnoid haemorrhage and mandates an urgent non-contrast CT head.
Worst headache of his life, at the back of the head: occipital thunderclap severity separates this from tension or migraine headache and raises pre-test probability sharply.
Neck stiffness and photophobia: meningism from blood in the subarachnoid space supports haemorrhage, though meningitis remains a differential.
Briefly lost consciousness as the headache struck: transient loss of consciousness at onset implies a sudden rise in intracranial pressure and predicts a larger bleed.
Similar milder sudden headache a week ago: A sentinel bleed makes aneurysmal haemorrhage far more likely and warns of imminent, often fatal, rebleeding.
Current smoker: smoking is the strongest modifiable risk factor for aneurysm formation and rupture.
Relative with a brain aneurysm: family history of intracranial aneurysm materially raises the probability of aneurysmal subarachnoid haemorrhage.
Becoming drowsy and losing the thread: A falling conscious level suggests rebleeding or hydrocephalus and demands urgent neurosurgical and critical care escalation.

Red flags you must not miss

The case marks these as must-elicit. They only come out if you ask.

Briefly lost consciousness as the headache struck.
Similar milder sudden headache a week ago.
Becoming drowsy and losing the thread.

Investigations and what they showed

CSF xanthochromia: CSF spectrophotometry detects xanthochromia (bilirubin from broken-down blood), perform the lumbar puncture at least 12 hours after onset if the CT is negative. Why it helps: when the CT head is negative but suspicion persists, LP with spectrophotometry for xanthochromia confirms/excludes SAH (and distinguishes true SAH from a traumatic tap).
CT head: Hyperdense (bright) acute blood filling the basal cisterns, Sylvian fissures and sulci, the 'star' pattern of aneurysmal subarachnoid haemorrhage. Why it helps: the immediate, first-line investigation, an urgent non-contrast CT head; sensitivity is highest within the first 6 hours and falls with time, so a negative early scan does not fully exclude SAH.
CT angiogram head (circle of Willis): Identifies the culprit cerebral (berry) aneurysm and its anatomy.
MRI brain: FLAIR shows hyperintense subarachnoid blood in the sulci/cisterns and SWI shows blooming (susceptibility) from the haemorrhage; more sensitive than CT for subacute/small bleeds. Why it helps: FLAIR/SWI MRI is highly sensitive for subarachnoid blood, useful when the CT is negative/late and to look for an underlying cause.
Inspect the patient's posture and position: He lies very still, curled on his side with his eyes screwed shut and a forearm across his face, and he resists being moved or sat forward. Why it helps: the posture of meningism and photophobia. Keeping absolutely still because any movement worsens the headache is the bedside signature of blood irritating the meninges, a very different picture from the restless pacing of cluster headache.
Inspect the patient's level of alertness and demeanour: He is rousable and answers, but keeps drifting off mid-sentence and losing the thread, and looks frightened and increasingly unwell. Why it helps: this is the red flag that upgrades him from urgent to emergency. A falling conscious level after a subarachnoid haemorrhage means rebleeding, hydrocephalus or rising intracranial pressure, it demands an immediate CT and a neurosurgical call, not observation.
Inspect the neck: He holds his neck rigidly and will not tuck his chin to his chest; passive flexion is met with involuntary resistance and pain. Why it helps: meningism from blood in the subarachnoid space. It takes hours to develop, so its absence early on means nothing, but when present with a thunderclap headache it is close to diagnostic and mandates urgent imaging.
Inspect the eyes: On fundoscopy there may be a subhyaloid (pre-retinal) haemorrhage, a well-defined, boat-shaped or dome-shaped pool of blood lying in front of the retina, often with a flat upper fluid level, sometimes obscuring the vessels beneath it. Why it helps: A subhyaloid haemorrhage (Terson's syndrome when vitreous blood is present) is caused by the abrupt spike in intracranial pressure and is effectively pathognomonic of subarachnoid haemorrhage. Finding one at the bedside clinches the diagnosis before the scanner.
Inspect the face: Grimacing and sweaty, brow furrowed, wincing whenever the cubicle light falls on him or he is asked to move his head. Why it helps: visible photophobia and severe pain in a man who says he rarely gets headaches. The mismatch between his usual state and this presentation is the whole reason to suspect a bleed rather than a benign headache.
Inspect the bedside and surroundings: The overhead light has been switched off and the curtains pulled; there is a used vomit bowl at the bedside. Why it helps: the environment is doing the examining for you, a patient who has darkened his own cubicle is telling you he is photophobic, and the bowl corroborates the vomiting at onset.
Inspect the vomitus: Gastric contents only, no fresh blood, no coffee grounds and no bile-stained faeculent material. Why it helps: confirms the vomiting is a consequence of raised intracranial pressure rather than a gastrointestinal cause, and keeps the focus on the head.

Imaging findings

ECG (bedside 12-lead): May show ST/T changes, QT prolongation or arrhythmia (neurogenic cardiac effects); may be normal.

Why the diagnosis is subarachnoid haemorrhage

The decisive diagnosis is subarachnoid haemorrhage, a sudden, severe, maximal-in-seconds ('thunderclap') 'worst-ever' headache, classically occipital and often during exertion, with vomiting, meningism (neck stiffness, photophobia), transient loss of consciousness and a possible preceding sentinel bleed, on a background of hypertension, smoking, family history/polycystic kidney disease. 'Thunderclap headache' is the correct syndromic umbrella but not a diagnosis, its differential includes SAH, reversible cerebral vasoconstriction, venous sinus thrombosis and arterial dissection, and SAH is the one you must not miss. Investigate with an urgent non-contrast CT head (most sensitive <6 hours); if negative but suspicion persists, do a lumbar puncture ≥12 hours after onset for xanthochromia.

Subarachnoid haemorrhage at a glance

What it is

Most spontaneous cases (around 85%) are caused by a ruptured berry (saccular) aneurysm on the circle of Willis.

Pathogenesis

A weak point in an intracranial artery wall, usually at a vessel branch point, balloons out into an aneurysm over years. Rupture releases arterial blood directly into the CSF-filled subarachnoid space at systemic pressure, causing a sudden rise in intracranial pressure, the physiological basis of the instantaneous, maximal "thunderclap" headache, and can trigger a cascade of rebleeding, obstructive hydrocephalus, and delayed vasospasm days later.

Who it affects

SAH affects roughly 9 per 100,000 people per year, more often women, typically in the 40s to 60s. Risk is higher with hypertension, smoking, excess alcohol, a family history of SAH or aneurysm, and polycystic kidney disease.

How serious it is

SAH is a neurosurgical emergency with high mortality, historically 40 to 50%, and roughly a quarter of survivors have lasting disability. A preceding sentinel headache (a smaller warning leak) may occur days to weeks before the major bleed and is easily missed.

Causes and risk factors

A ruptured berry aneurysm accounts for most spontaneous cases; arteriovenous malformations are a less common cause. Hypertension, smoking, heavy alcohol use, a family history and polycystic kidney disease all raise aneurysm risk, and rupture can be provoked by acute exertion or a Valsalva manoeuvre.

Investigations and lab tests

An urgent non-contrast CT head is the immediate investigation, most sensitive within 6 hours of onset. If the CT is negative but suspicion persists, a lumbar puncture at least 12 hours after onset looks for xanthochromia, the yellow discolouration from haemoglobin breakdown that distinguishes true SAH from a traumatic tap. Once SAH is confirmed, CT angiography locates the aneurysm to plan how it will be secured.

At a glance: First: non-contrast CT head. If negative but suspicious: LP after 12h for xanthochromia. Confirmed: CT angiography.

Teaching points

A sudden, severe, maximal-in-seconds 'worst headache of my life' (thunderclap), especially occipital, exertional, with vomiting, neck stiffness, photophobia or transient loss of consciousness, is subarachnoid haemorrhage until proven otherwise.
Ask about a preceding sentinel headache (a warning leak days to weeks before) and the risk factors: hypertension, smoking, family history and polycystic kidney disease.
The immediate investigation is an urgent non-contrast CT head, most sensitive within 6 hours; sensitivity falls with time.
If the CT is negative but suspicion persists, do a lumbar puncture at least 12 hours after onset and look for xanthochromia (which distinguishes true SAH from a traumatic tap).
Never label a first thunderclap headache 'migraine' without excluding SAH.

Practise a similar case

Reading that the pain was occipital and maximal within seconds on exertion is easy on the page. Under a bit of time pressure, you need to ask about that thunderclap timing, the vomiting, and any sentinel headache a week earlier, without being led by the stem. Try taking a focused history from another neurology patient now.

Here's one from the same specialty, with the diagnosis left for you to find. Your next patient is a 62-year-old man with headaches that have been getting worse over the past 4 weeks. Take this patient's history in Diagnosica. It's free to start, no card needed.

Subarachnoid haemorrhage case presentation: history, findings and tests