6.2.2 Acute headache attributed to non-traumatic subarachnoid haemorrhage (SAH)

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Non-traumatic subarachnoid haemorrhage (SAH) is distinguished from non-traumatic convexal subarachnoid haemorrhage (cSAH). The latter disorder can present with highly variable clinical and radiological features according to its various underlying causes, which include reversible cerebral vasoconstriction syndrome (RCVS), cerebral amyloid angiopathy (CAA), endocarditis and cerebral venous thrombosis. Patients with aura-like attacks, cSAH and CAA should be coded as 6.8.4 Migraine-like aura attributed to cerebral amyloid angiopathy. Patients with headache, cSAH and RCVS should be coded as 6.7.3. Headache attributed to reversible cerebral vasoconstriction syndrome.


Headache caused by non-traumatic subarachnoid haemorrhage (SAH), typically severe and sudden in onset, peaking in seconds (thunderclap headache) or minutes. It can be the sole symptom of non-traumatic SAH.

Diagnostic criteria:
  1. Any new headache fulfilling criteria C and D
  2. Subarachnoid haemorrhage (SAH) in the absence of head trauma has been diagnosed
  3. Evidence of causation demonstrated by at least two of the following:
    1. headache has developed in close temporal relation to other symptoms and/or clinical signs of SAH, or has led to the diagnosis of SAH
    2. headache has significantly improved in parallel with stabilization or improvement of other symptoms or clinical or radiological signs of SAH
    3. headache has sudden or thunderclap onset
  4. Either of the following:
    1. headache has resolved within 3 months1
    2. headache has not yet resolved but 3 months have not yet passed1
  5. Not better accounted for by another ICHD-3 diagnosis2;3.
  1. The 3 months should be counted from stabilization, spontaneously or through treatment, rather than onset of the subarachnoid haemorrhage (SAH).
  2. Diagnosis of SAH is confirmed by non-contrast-enhanced CT scan: sensitivity is close to 99% in the first 6 hours after onset, 98% at 12 hours and 93% at 24 hours (but dropping to 50% at 7 days). When CT results are nondiagnostic, lumbar puncture is essential: xanthochromia is present in all cases with aneurysmal SAH when cerebrospinal fluid (CSF) is collected between 12 hours and two weeks after the onset of symptoms and analysed spectrophotometrically. MRI is not indicated as an initial diagnostic test for SAH; however, FLAIR and gradient-echo T2-weighted images may be useful when the CT is normal and the CSF abnormal.
  3. In the presence of non-traumatic convexal subarachnoid haemorrhage, older age, sensorimotor dysfunction, stereotyped aura-like spells and absence of significant headache suggest cerebral amyloid angiopathy as the underlying cause. Younger age and recurrent thunderclap headache predict reversible cerebral vasoconstriction syndrome.

Non-traumatic subarachnoid haemorrhage (SAH) is one of the most common causes of persistent, intense and incapacitating headache of abrupt onset (thunderclap headache), and is a serious condition (mortality is 40-50%, with 10-20% of patients dying before arriving at hospital; 50% of survivors are left disabled).

6.2.2 Acute headache attributed to non-traumatic subarachnoid haemorrhage may nonetheless be moderate and without any associated signs. The abrupt onset is the key feature. Accordingly, any patient with headache of abrupt onset or thunderclap headache should be evaluated for SAH.

Delayed diagnosis often has a catastrophic outcome: SAH is a neurointerventional emergency. However, initial misdiagnosis occurs in one quarter to one half of patients, the most common specific misdiagnosis being migraine. The most common reasons for misdiagnosis are failure to obtain appropriate neuroimaging, or misinterpretation of it, or failure to perform lumbar puncture in cases where this is required.

After diagnosis of SAH, the next urgent step is to identify a ruptured aneurysm (80% of cases of spontaneous SAH result from ruptured saccular aneurysms). In patients who are initially misdiagnosed and in whom SAH is belatedly recognized when they present again a few days later, there is often no aneurysm and no cause identifiable for the SAH.