By Professor Tim Harris professor in emergency medicine, Queen’s Mary University London and Bart’s Health NHS Trust.
Mr David Sayer is specialist registrar in neurosurgery, Queen’s Hospital, Romford
Professor in emergency medicine, Tim Harris, and specialist registrar in neurosurgery Mr David Sayer discuss the signs and the pitfalls in diagnosing subarachnoid haemorrhage
SAH is a devastating disease with a mortality of 45% and from which 30% of the survivors will have severe disability.3 The chance of an aneurysm which has had a small rupture, having a further bleed is approximately 1.5% per day for the first two weeks. Early treatment with either surgery or angiographic coiling aims to prevent further bleeding and serious neurological damage, thus early diagnosis is important.
The worse outcome is death or disability following a re-bleed in a well patient. The patient who has a grade 1 SAH (GCS 15 with no deficit) has the most to gain from prompt treatment of the aneurysm and the potential to lead a completely normal life. If the first bleed is missed and a subsequent one happens, the risk is highest in the first two weeks, then this has a significant chance of causing death or disability, which is preventable. These, as they are neurologically intact, are the patients most likely to present to primary care.
SAH is most commonly due to rupture of a Berry aneurysm, causal in around 85%. 10% are idiopathic perimesencepalic bleeds and around 5% are due to rarer causes, including intracranial artery dissection, arterio-venous malformation, tumours, angiitis, cerebral venous thrombosis and RCVS. The incidence is around 6-8:100000/year.1
Asymptomatic Berry aneurysms are common, occurring in 3-6% of the population.2
The prognosis for non-aneurysmal SAH is good.
Symptoms and signs
Acute severe headache
Patients with SAH usually complain of having an acute severe headache, but can present with
- altered consciousness
The classical presentation is a ‘thunderclap headache’, defined as a headache that reaches 7/10 or more on a 0-10 pain severity scale within one minute of onset.4 It lasts from minutes to days.
SAH is identified in around 10-25% of such presentations and in 10-12%, other serious diagnoses are found.5,6
Thunderclap headache requires urgent referral to the emergency department for evaluation, regardless of associated findings such as neck stiffness or normal cerebral function. Urgent referral should still be made for patients attending in the days post thunderclap headache, as this may represent a ‘warning bleed’ for SAH.
Less severe headache
SAH may present with less severe headache. The so called sentinel bleed, in which a small leak of blood from an aneurysm occurs some days or weeks prior to a larger bleed, is well described and sees clinicians have a low threshold for investigation of headache.6
- Medication overuse headache
- Acute trigeminal autonomic neuralgias (such as cluster type headache)
- Musculoskeletal disease
- Benign sex headache
- Intracerebral haemorrhage
- Extradural haemorrhage
- Cervical artery dissection
- Aneurysm of intracranial vessels.
- Temporal arteritis
- Cerebral venous sinus thrombosis
- Pituitary apoplexy
- Space occupying lesions
- Reversible cerebral vasoconstriction syndrome (RCVS).5
To avoid missing SAH, GPs should have a low threshold for the investigation of headache, not simply thunderclap headache, even if the patient being assessed has a history of headache in the past.
A headache of different character to usual is most safely assumed as potentially representing a different aetiology.
Only around 70% SAH presents with isolated headache and this meets the definition for ‘thunderclap headache’ in only 50%.
A non-contrast CT brain scan is the key to most headache diagnoses. A lumbar puncture (LP) is commonly recommended if the CT scan has not identified a cause for the headache.
CT accuracy for diagnosing SAH falls with time from headache onset – approaching 100% if performed within six hours but falling to 90% to around 24-48 hours and 50% by one week. 7,8
The LP is performed 12-hours post-headache in order to identify xanthochromia. CSF is sent to the laboratory for cell counts and spectrophotometry. If the latter identifies bilirubin this is taken as diagnostic of SAH. However, the LP is non-diagnostic in up to one third of cases.
The requirement for an LP on all CT negative patients with a history suggestive of SAH has been recently challenged with a large prospective cohort study suggesting that CT scanning may exclude SAH if CT is performed within six hours of onset. Some departments offer alternative further investigations for patients presenting with thunderclap headache, such as MRA or CT angiography. If the non-contrast CT or LP suggest SAH then the investigation of choice to identify the cause of SAH is a CT angiogram.
Five key questions
- Is this your worse ever headache and different to your previous headaches?
- How long did it take to reach peak intensity? (SAH peaks within minutes)
- Are there any features of meningeal irritation? For example, neck stiffness, photophobia, nausea and vomiting
- Was there any associated loss of consciousness, no matter how brief?
- Any family history of brain haemorrhage? There is an increased chance of aneurysm if two first degree relatives have suffered from a subarachnoid haemorrhage.
Five red herrings
- In patients with previous headaches, these can confuse the issue. The biggest risk is failure to consider the diagnosis. In particular, a different headache from usual is important.
- Are there any focal neurological deficits? This points to a different diagnosis as patients presenting to a GP surgery with SAH are unlikely to have a focal deficit, these tend to happen in poorer grade patients. The exception is an acute third nerve palsy which can signify a posterior communicating artery aneurysm.
- Treat falls with suspicion. Did the event happen before and caused the fall, rather than the headache being a result of a bang to the head.
- Increased blood pressure often occurs in SAH. Be wary of attributing headache to hypertension.
- Fevers, particularly high, suggest an alternative diagnosis such as meningitis.
Professor Tim Harris is professor in emergency medicine, Queen’s Mary University London and Bart’s Health NHS Trust. Mr David Sayer is specialist registrar in neurosurgery, Queen’s Hospital, Romford