Response

摘要

Editor – We thank Dr Thompson for the interest in our paper and he raises some valid points.1 Indeed, we have not strictly adhered to the inclusion criteria of the original Ottawa rule study from Perry et al.2 Using the clinical information provided on the computed tomography (CT) request we attempted to ascertain, in so far as possible, those patients undergoing a CT of the head for the investigation of subarachnoid haemorrhage (SAH). We included patients whose requests included a working diagnosis of SAH or clinical information such as sudden onset headache, thunderclap headache or ‘worst headache of life’. As a retrospective study this represented our best estimation of the patient cohort undergoing CT of the head for the investigation of SAH, although as the author rightly states these patients may not truly have been suspected of this diagnosis. This is evident in the subsequently low proportion of patients in whom a lumbar puncture was performed (32%). We are, as radiologists and as researchers, limited by the clinical information that has been provided in the request. However, a subgroup analysis of patients (n=65; 18%), who do meet the strict inclusion criteria has been performed and detailed in our article. In short, the Ottawa rule was 100% sensitive in this cohort and missed no cases of SAH.