History and exam

Key diagnostic factors

common

severe sudden-onset headache

  • Usually peaks within 1 to 5 minutes (thunderclap headache) and lasts more than an hour.[38][46][47]​​​ Headache typically presents alongside vomiting, photophobia, and non-focal neurological signs.[54]​​

    • Expert opinion is that the speed of onset is more diagnostic than the severity.[55]

  • If you suspect SAH, request an urgent non-contrast computed tomography (CT) head scan to be carried out as soon as possible.[38]​ This is the standard diagnostic test for SAH.[39]​[43]​​​ 

    • Diagnosis is confirmed by the hyperdense appearance of blood in the subarachnoid space/basal cisterns.[43]​​

Practical tip

A migraine may also be described as a sudden, severe headache and can also be associated with vomiting and photophobia but will usually have occurred previously. A history of migraine, however, does not preclude a non-migraine aetiology of headache, including SAH.

It is often more difficult to recognise SAH in people with an explosive headache as the only complaint. SAH is the cause in 11% to 25% of patients with thunderclap headache.[56]

depressed consciousness/loss of consciousness

  • Caused by blockage of the normal cerebrospinal fluid circulation by blood in the subarachnoid space.

  • On admission, up to two-thirds of people with SAH have a depressed level of consciousness, half of whom are in a coma.[57]

    • Altered consciousness is a finding that can resemble stroke (ischaemic or haemorrhagic).

    • Loss of consciousness is independently associated with death or poor functional outcomes at 1 year.[12]​[58]​​

  • Be aware that unconscious patients still need a neurological examination to assess reflexes, tone, and pupil changes. In patients with Glasgow Coma Scale score ≤8 or falling: [ Glasgow Coma Scale Opens in new window ]

    • Check pupils for size, shape, and reactivity to light every 20 minutes

    • Discuss any pupil changes with a neurosurgeon

      • Fixed and dilated pupils in comatose patients are associated with poor prognosis, especially when present bilaterally.[50]

Practical tip

The patient's level of consciousness is the most predictive factor of outcome as it is correlated directly with the degree of neurological dysfunction at time of first presentation.[58] A poor neurological status on admission predicts cardiac abnormalities thought to be secondary to overwhelming sympathetic activation.[59][60][61][62]

neck stiffness and muscle aches (meningismus)

  • A clue to diagnosis only when associated with sudden, severe headache.

  • The patient may have limited or painful neck flexion on examination.[38]

  • A finding that can resemble infective meningitis.

presence of risk factors

Take a comprehensive history to identify risk factors for SAH, most notably:

  • Age ≥50 years old[43]

  • Female sex[71]

  • Smoking[30][31][32][33][34][47]

  • Hypertension[30][31][32][33][34][47]

  • Alcohol misuse[34]

  • First-degree relative of a patient with a history of SAH[69][70]

  • Genetic connective tissue disorders and other systemic disorders associated with aneurysm formation, or other vascular abnormalities (e.g., Marfan syndrome, Ehlers-Danlos syndrome, pseudoxanthoma elasticum, neurofibromatosis type I, and polycystic kidney disease)[41]

  • Acute cocaine use[73][74]

  • Exposure to adrenergic or serotonergic drugs.[42]

uncommon

eyelid drooping, diplopia with mydriasis, orbital pain

  • Caused by compression of the third cranial nerve by the aneurysm.

  • Signals a posterior communicating artery aneurysm compressing the ipsilateral third cranial nerve.

  • Given their proximity to the third cranial nerve, aneurysms arising from the superior cerebellar artery or posterior cerebral artery can result in the same.

Other diagnostic factors

common

photophobia

  • A common symptom seen in many neurological disorders, particularly in people with migraine headache.

  • In SAH, photophobia can be due to irritation of the meninges by blood in the subarachnoid space.

nausea/vomiting

  • Due to irritation of the cerebral cortex caused by the haemorrhage.

confusion

  • Caused by blockage of the normal cerebrospinal fluid circulation by blood in the subarachnoid space.

uncommon

history of sentinel headaches

  • Sentinel (warning) headaches may represent minor haemorrhages. These headaches are sudden, intense, and persistent; precede the SAH by days or weeks; and resolve by themselves.

  • Occur in 15% to 60% of patients with spontaneous SAH.[2]

Practical tip

About 1 in 20 cases of SAH are missed during an emergency department visit.[68] This is especially the case in people with isolated headache and a normal Glasgow Coma Scale score.[56] Beware that sentinel headaches can be mistaken for benign headaches. 

seizures

  • Seizures at the onset of SAH occur in around 7% of patients.[63] About 10% develop seizures in the first few weeks.[64]

  • Associated with a large haemorrhage and subdural haematoma.[65]

diplopia

  • Caused by sixth cranial nerve palsies due to raised intracranial pressure.

visual loss

  • Intraocular haemorrhages (secondary to increased intracranial pressure) are seen in 10% to 40% of patients with SAH.[66] They  cause visual loss in the affected eye, a finding that can resemble stroke (ischaemic or haemorrhagic). This is associated with worse prognosis and increased mortality.[66]

agitation

  • Due to irritation of the cerebral cortex caused by the haemorrhage.

  • A finding that can resemble stroke (ischaemic or haemorrhagic).

focal neurological deficits

  • One in every 10 patients with aneurysmal SAH presents with focal neurological deficits (e.g., unilateral loss of motor function, loss of visual field, aphasia). These findings resemble stroke (ischaemic or haemorrhagic).

  • Independently associated with a poor outcome.[67]

Use of this content is subject to our disclaimer