6.2.2 Headache attributed to non-traumatic subarachnoid haemorrhage (SAH)

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

Diagnostic criteria:
A. Any new headache fulfilling criterion C
B. Subarachnoid haemorrhage (SAH) in the absence of head trauma has been diagnosed
C. 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

D. Not better accounted for by another ICHD-3 diagnosis.

Subarachnoid haemorrhage (SAH) is the most common cause of persistent, intense and incapacitating headache of abrupt onset (thunderclap headache), and is a serious condition (mortality rate is 40-50% and 10-20% of patients die before arriving at hospital; 50% of survivors are left disabled).

6.2.2 Headache attributed to non-traumatic subarachnoid haemorrhage (SAH) may nonetheless be moderate and without any associated signs. The abrupt onset is the key feature. Any patient with headache of abrupt onset or thunderclap headache should be evaluated for SAH. Diagnosis is confirmed by non-contrast-enhanced CT scan, which has a sensitivity of 98% in the first 12 hours after onset (dropping to 93% at 24 hours and 50% at seven days). If CT results are nondiagnostic, a lumbar puncture is essential. Xanthochromia is present in 100% of 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.

Initial misdiagnosis occurs in one quarter to one half of patients; the most common specific misdiagnosis is migraine, but often, in these cases, no cause is identified. The most common reasons for misdiagnosis are failure to obtain appropriate neuroimaging, or misinterpretation, or failure to perform a lumbar puncture in cases where this is required. Delayed diagnosis often has a catastrophic outcome.

SAH is a neurointerventional emergency. 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).