Sentinel headache.

Patients with subarachnoid haemorrhage (SAH) frequently describe the occurrence of an underestimated or even ignored severe headache in the days or weeks preceding the bleeding. If recognised early, this warning headache might lead to specific investigations and, if indicated, a surgical approach might avoid a dramatic haemorrhagic event. In a recent and exhaustive systematic review, the incidence of a sentinel headache (SH) was evaluated in a range of 10-43% of SAH patients. SH seems to be due to a minor bleeding from a leak of a berry aneurysm and usually occurs in the preceding two weeks. Such a period is similar to the one for rebleeding in SAH and supports the hypothesis of the warning leak. Nevertheless, a warning headache can precede a SAH in unruptured aneurysm even without a minor bleeding. Underestimation or misdiagnosis of SH depends on incorrect evaluation of the headache characteristics (unusual, severe, abrupt, thunderclap), overestimation of cranial CT sensitivity (false negative increasing over the elapsing time), failure to perform lumbar puncture (LP) in patients with negative CT, incorrect evaluation of CSF findings (xanthochromia may be absent in the first 12 h) and failure to differentiate traumatic tap from true SAH. Considering the diagnosis of SH in all cases of a severe, sudden-onset (thunderclap) headache, and performing all the appropriate diagnostic exams, including LP if necessary, could prevent subsequent massive bleeding and its invalidating or fatal consequences.