Best evidence topic reports. BET 2: does a normal CT scan within 6 h rule out subarachnoid haemorrhage?

A short cut review was carried out to establish whether a normal CT scan within 6 h of onset of a severe, sudden onset headache can be used to rule out a subarachnoid haemorrhage. Four studies were directly relevant to the question. The author, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of these papers are tabulated. The clinical bottom line is that a CT scan performed on a third generation scanner with thin slices, reported by a radiologist experienced in reporting CT brain scans, within 6 h of onset of the headache can be used to rule out a subarachnoid haemorrhage.