CT-negative, lumbar puncture-positive and CTA-negative patients have a low risk of aneurysms.
We are grateful to Bakker et al. for their prospective study in this area.
Two months prior to this, we published on the topic of CT-negative, lumbar puncture-positive and CT-angiography (CTA) negative patients. Such patients had been reported in 98 published cases. No causative aneurysms were found in neither these nor in the 9 cases which we identified.
Bakker et al report 37 additional patients in the section 'Imaging' on page 3 of their article. These 37 patients had digital subtraction angiography (DSA) within 48 hours and no vascular lesions were found. This brings the number of published cases to 144.
We recommend double-reporting of the CT angiogram in these apparently normal scans. The risk:benefit ratio of proceeding to DSA in such patients is debatable due to the relatively small number of published cases.
Arnab K. Rana[a], Helen E. Turner[b] and Kevin A. Deans[b]
a Aberdeen Biomedical Imaging Centre, University of Aberdeen, Lilian Sutton Building, Foresterhill, Aberdeen, AB25 2ZD, UK
b Department of Clinical Biochemistry, Aberdeen Royal Infirmary, Foresterhill, Aberdeen, AB25 2ZN, UK
 Bakker NA, Groen RJM, Foumani M et al. Appreciation of CT- negative, lumbar puncture-positive subarachnoid haemorrhage: risk factors for presence of aneurysms and diagnostic yield of imaging. J Neurol Neurosurg Psychiatry doi:10.1136/jnnp-2013-305955.
 Rana AK, Turner HE and Deans KA. Likelihood of aneurysmal subarachnoid haemorrhage in patients with normal unenhanced CT, CSF xanthochromia on spectrophotometry and negative CT angiography. J R Coll Physicans Edinburgh 2013; 43: 200-6.
Conflict of Interest: