Pitfalls in the use of spiral CT for identification of intracranial aneurysms

We describe problems encountered in our first 136 patients, with 95 aneurys ms, who underwent spiral CT for investigation of possible aneurysms involvi ng the circle of Willis and adjacent major vessels? and who had surgical an d/or angiographic confirmation. There were seven false-positive cases, of w hich the first three could be explained by operator inexperience. There wer e four false negatives, all small aneurysms; two were not seen because of o perator error and two were hidden by an adjacent larger aneurysm. Clip arte facts prevented diagnostic studies in six of 21 postoperative studies. One aneurysm was outside the CT field of view, being on a pericallosal artery. One basilar artery tip aneurysm was excluded from the field of the CT study because of a planning error. Inspection of the axial source images is crit ical if the diagnosis of small or thrombosed aneurysms is to be made. Close attention to image acquisition and computer modelling is required to reduc e errors in spiral CT angiography of intracranial aneurysms.