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PAPERS: Marie E Westwood, Steven Kelly, Elizabeth Berry, John M Bamford, Michael J Gough, C Mark Airey, James F M Meaney, Linda M Davies, Jane Cullingworth, and Michael A Smith Use of magnetic resonance angiography to select candidates with recently symptomatic carotid stenosis for surgery: systematic review BMJ 2002; 324: 198 [Abstract] [Full text]

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Non-invasive vascular imaging should replace conventional angiography in assessing carotid stenosis

Y. C. Chan   (6 February 2002)

Non-invasive vascular imaging should replace conventional angiography in assessing carotid stenosis 6 February 2002
Y. C. Chan, SpR in General Surgery, South-East Thames Deanery, King's College Hospital, Denmark Hill, London SE5 9RS. Send response to journal: Re: Non-invasive vascular imaging should replace conventional angiography in assessing carotid stenosis	I congratulate Westwood et al. on their excellent review of the subject1. There is no doubt that non-invasive imaging methods [such as the use of contrast-enhanced MR angiography (MRA), being free of irradiation with a short acquisition time] is going to replace conventional angiography as the gold standard for evaluating the degree of carotid artery stenosis. However, concerns are recently raised that MRA tends to overestimate the percentage stenosis when compared to intra-arterial angiography, and MRA can cause significant diagnostic errors in very tight carotid stenosis2. This error can be overcome by the combined of MRA and duplex ultrasonography, which has a similar diagnostic accuracy to angiography, yet without imposing a small but definite 1% risk of stroke and death3. MRA should be the technique of choice in younger patients or those with renal impairment since the gadolinium-based contrast agents are non-ionizing and do not cause nephrotoxicity. The newly developed dynamic MRA ensures even higher resolution in providing rapid and excellent vascular definition. Helicoidal CT, with its spiral acquisition protocols and image processing techniques, is an alternative noninvasive method providing a reliable evaluation of carotid artery stenosis by analyzing both the axial CT images and the three-dimensional reconstruction. Although this requires a radiation dose and injection of an iodinated contrast agent, examination times are shorter than those typically required for MRA, and may be more suited to examinations of acute conditions4. It is also a valuable diagnostic modality for screening patients for concurrent intracranial aneurysms or arteriovenous malformations. Recently, an increasing number of institutions are using duplex ultrasound as the single independent preoperative test of carotid disease, and is replacing conventional angiography as the first-choice technique for preoperative assessment5. Despite controversy among vascular surgeons and other carotid specialists, there is now no reason why duplex ultrasonography can not be used as the sole preoperative imaging test, if there is institutional validation and ongoing quality assurance. Not only is it cheaper than MRA, duplex ultrasound has the added advantage of examining distinct echo-morphologic characteristics of plaques, thereby distinguishing between the symptomatic hypo-echoic plaques from the asymptomatic hyper-echoic plaques6. In addition, perioperative use of transcranial doppler, whilst examining a haemodynamically significant carotid lesion, can provide more information than two-dimensional imaging studies. It can therefore be argued that non-invasive imaging modalities together with transcranial doppler is now replacing conventional angiography as the 'gold standard' for evaluation of extra- and intra- cranial carotid flow. References 1. Westwood ME, Kelly S, Berry E, Bamford JM, Gough MJ, Airey CM, Meaney JF, Davies LM, Cullingworth J, Smith MA. Use of magnetic resonance angiography to select candidates with recently symptomatic carotid stenosis for surgery: systematic review. BMJ. 2002; 324: 198. 2. Wardlaw JM, Lewis SC, Humphrey P, Young G, Collie D, Warlow CP. How does the degree of carotid stenosis affect the accuracy and interobserver variability of magnetic resonance angiography? J Neurol Neurosurg Psychiatry 2001; 71: 155-160. 3. Back MR, Wilson JS, Rushing G, Stordahl N, Linden C, Johnson BL, Bandyk DF. Magnetic resonance angiography is an accurate imaging adjunct to duplex ultrasound scan in patient selection for carotid endarterectomy. J Vasc Surg 2000; 32: 429-438. 4. Prokop M, Debatin JF. MRI contrast media - new developments and trends. CTA vs. MRA. Eur Radiol 1997; 7 Suppl 5: 299-306. 5. Melissano G, Castellano R, Zucca R, Chiesa R. Results of carotid endarterectomy performed with preoperative duplex ultrasound assessment alone. Vasc Surg 2001; 35: 95-101. 6. Tegos TJ, Kalomiris KJ, Sabetai MM, Kalodiki E, Nicolaides AN. Significance of sonographic tissue and surface characteristics of carotid plaques. Am J Neuroradiol 2001; 22: 1605-12.