A. Any new headache fulfilling criterion C
B. An unruptured saccular aneurysm 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 unruptured saccular aneurysm, or has led to its diagnosis
2. either or both of the following:
a) headache has significantly worsened in parallel with other symptoms or clinical or radiological signs of growth of the saccular aneurysm
b) headache has resolved after treatment of the saccular aneurysm
3. either or both of the following:
a) headache has sudden or thunderclap onset
b) headache is associated with a painful IIIrd nerve palsy
D. Not better accounted for by another ICHD-3 diagnosis, and intracranial haemorrhage and reversible cerebral vasoconstriction syndrome have been excluded by appropriate investigations.
Headache is reported by approximately one fifth of patients with unruptured cerebral aneurysm, but whether this association is incidental or causal is an unresolved issue.
6.3.1 Headache attributed to unruptured saccular aneurysm usually has no specific features. On the other hand, a new-onset headache can reveal a symptomatic but unruptured saccular aneurysm. A classic variety is acute IIIrd nerve palsy with retro-orbital pain and a dilated pupil, indicating an aneurysm of the posterior communicating cerebral artery or termination of the carotid artery. Such painful IIIrd nerve palsy is an emergency, signalling impending rupture or progressive enlargement of the arterial malformation.
Several retrospective studies have shown that about half of patients with an aneurysmal subarachnoid haemorrhage reported the occurrence of a sudden and severe headache within the four weeks prior to the diagnosis of aneurysmal rupture. Setting aside the possibility of memory biases, this suggests these headaches are due to sudden enlargement of the arterial malformation (“sentinel headache”) or to mild subarachnoid haemorrhage that is not diagnosed as such (“warning leak”). Evidence for the existence of sentinel headaches is poor. Moreover, the term “warning leak” should not be used, because a leak indicates a subarachnoid haemorrhage. Given that at least one in three patients with aneurysmal subarachnoid haemorrhage is initially misdiagnosed, and given the risks of re-bleeding, patients with sudden severe headaches should undergo complete investigation, including cerebral imaging, CSF study and cerebral angiography (MRA or CT angiography).