Throwing out the baby with the bathwater

Sir We disagree with the opinion of Turner and Murk (Br J Surg 1989; 76: 1247-50), that intravenous digital subtraction angiography (IVDSA) should not be used to assess the carotid arteries in stroke patients because of unsatisfactory safety and accuracy. On the question of safety, two of the most unfavourable publications were cited in which three neurological complications were reported in 602 examinations. Each happened some time after the completion of the study unlike those in intra-arterial angiography which usually happen during the procedure, characteristically immediately after an injection of contrast material, or saline. Your readers are urged to study the report of a multi-centre prospective study in which not one neurological complication occurred in several thousand IVDSA examinations and evanescent chest pain, which occurred in 0.2 per cent, was the only potentially serious systemic event recorded (Stevens et al.'). Why some workers have registered many more serious events is conjectural. The total dose of iodine given in an average IVDSA is lower than the dose recommended by some workers to enhance a routine computed tomographic brain scan. Perhaps the use of ionic rather than non-ionic contrast material was important, although far larger comparative trials have found only small differences in the low incidences of only minor complications recorded using either media (Sackett et a1.2, Seyferth et ~ 1 . ~ ) . On the question of accuracy, it is time it was accepted that precise grading of a carotid stenosis is not of clinical value. The few studies which consider age matched controls indicate that only severe stenosis correlates with ipsilateral cerebral hemisphere events and pathological evidence of brain damage, and then only weakly, and that all grades of stenosis less than this do not (Brown et u I . ~ , Schwartz and Mitchell5). Furthermore, even the best quality cut film angiography is unreliable at identifying ulcerated atheroma and adherent thrombus, and also may underestimate a stenosis (Kricheff6), yet so often this is taken as the standard against which other techniques are compared. Image quality in the average IVDSA is inferior to intra-arterial techniques but this does not mean the method is not clinically useful, and the 5-10 per cent of examinations which are non-diagnostic are usually easily recognizable as such by all who view them. We agree with Turner and Murk that the frequency ofcomplications with intra-arterial techniques is unacceptably high for screening. Carotid sonography may be satisfactory in specialized units, but usually shows only a small part of the vascular tree and can be. unreliable in less committed hands. Importantly the reliability of each result cannot be evaluated readily by the referring clinician. Misconceptions abound about the importance of proximal atheroma as a cause of cerebral symptoms and a realistic attitude towards our diagnostic aims is urgently required. We wish to identify not simply atheroma, which is common, but clinically relevant atheroma which is much less common. We believe IVDSA to be a serviceable screening test for the following reasons: (1) It has an acceptably low morbidity; (2) It shows the entire vascular tree from aortic arch to Circle of Willis, and beyond; (3) It is less likely on the whole to produce an unrecognizably spurious result than carotid sonography; (4) Its sensitivity is such that it detects mainly severe atheroma which is more likely to be relevant; and (5) It can be the definitive contrast investigation in around 90 per cent of patients, including those having carotid endarterectomies (Stevens et a / . ' ) . Turner and Murie have advocated that we throw out the baby with the bathwater. We are saying throw out only the muddy water and keep this particular baby at least until something better comes along.