SAH can present in a number of different ways: from collapse with a reduced level of consciousness to acute confusion or seizures but, in those able to speak, the primary complaint is usually of sudden and severe headache .
Initial presentation and causes of non-traumatic SAH
Presentation to the ED with headache is common and represents 1-4% of attendances [23-25]. Causes range from benign tension headache or migraine to a catastrophic secondary cause including SAH.
Table 1: Important causes of secondary headache
|Vascular || |
- Stroke (ischaemic or haemorrhagic)
- Dissection of cranio-cervical arteries
- Hypertensive encephalopathy
- Giant cell arteritis
- Cerebral venous sinus thrombosis
- Pituitary apoplexy
|Infective || |
|Intracranial mass || |
|Idiopathic intracranial hypertension || |
|Acute angle closure glaucoma || |
|CO poisoning || |
|Spontaneous intracranial hypotension || |
SAH represents only 1-3% of all cases of ED headache though this may be as high as 12% if only worst ever headache is considered .
For more information on these topics, please see the sessions on Primary Headache and Secondary Headache in the Learning Curriculum.
Likelihood of SAH
The likelihood of SAH correlates well with a reduced Glasgow Coma Score (GCS) or the presence of abnormal neurological signs  but up to 50% of SAH patients have normal neurology at presentation [7,28].
Important correlates in the history are worst ever headache [26,27] particularly of rapid onset [28,29] and perhaps with associated seizure . Additionally, it has recently been described that the findings of age > 40 years, neck pain and stiffness, limited neck flexion or transient loss of consciousness are associated with increased chance of SAH .
Onset of SAH
Usually, the onset is within seconds though sometimes minutes . Expert opinion holds that, though the headache is usually awful, the suddenness of onset is more important than the severity in making the diagnosis .
A headache failing to reach maximal intensity within a few minutes is unlikely to be due to SAH [31,32]. Characteristically, the headache will last at least an hour [31,32] and usually 1-2 weeks .
Site and character of the headache are generally not helpful in making the diagnosis though, in the patient known to suffer from headaches, it is important to carefully elicit whether the onset, severity, quality and associated symptoms are typical or whether this presentation is different. Occasionally, the headache may be mild  or relieved with simple analgesia .
Association with physical exertion has been demonstrated [30,35] but most episodes of SAH occur at periods of relative inactivity .
The concept of the sentinel headache or herald bleed due to presumed aneurysm stretching or a small warning haemorrhage is a matter of some conjecture  and there are no other historical features that are helpful in the diagnosis [18,27].
The spectrum of clinical signs
|Fig 3: ECG in a lady with SAH showing widespread T wave inversion (click to enlarge) |
SAH may produce a wide spectrum of clinical signs. These may be specific e.g. subhyaloid haemorrhage and cranial nerve palsies or non-specific e.g. vomiting, pyrexia, meningism and visual disturbance.
SAH may cause hypertension or neurogenic pulmonary oedema and can mimic the ECG changes of acute myocardial ischaemia (Fig 3) or infarction leading to treatment delays. SAH is also a known cause of cardiac arrest .