doi: 10.1161/01.STR.0000026110.69908.5B
(Stroke. 2002;33:1948.)
© 2002 American Heart Association, Inc.
Letters to the Editor |
The Way Out
Institute of Diagnostic Radiology, Friedrich-Alexander-University Erlangen-Nürnberg, Germany, Institute of Neuroradiology, Oberösterreichische Landesnervenklinik, Linz, Austria
Vascular Surgery, Friedrich-Alexander-University Erlangen-Nürnberg, Germany
To the Editor:
We read with great interest the article by Qureshi et al1 and, in particular, the comments submitted by Ballotta et al2 as well as the response from Qureshi et al.2 Qureshi et al1 conclude in their paper that the "present accuracy of carotid Doppler ultrasound (DUS) in general practice does not justify its use as the sole basis of selecting appropriate patients for carotid intervention." Consequently, conventional angiography (CA) should be performed in every patient before a decision regarding intervention is made. Ballotta et al2 emphasized the high degree of accuracy of DUS (>90%) in accredited laboratories3,4 and regretted the "alarming" findings cited by Qureshi et al1 on the inaccuracy of DUS in general practice. However, these should not cast a shadow on the effectiveness of DUS as a stand-alone screening and diagnostic tool. In their reply,2 Qureshi et al counter this with the results of other studies with DUS misclassification rates of 28%.5 More recent studies are now actually correcting the excellent results published for previous studies downward, and confirming that these excellent figures are no longer tenable.6,7 Thus, if the indication for invasive therapy is based on ultrasound findings alone, we must consider the fact that a number of patients are needlessly subjected to invasive therapy even though they cannot possibly profit from the intervention (because they do not in reality have a high-grade stenosis at all). But they are still exposed to the risk. Alternatively, a stenosis may be incorrectly underestimated and the patient denied a logically invasive intervention. As Qureshi et al also warn in their reply,2 such a situation must be avoided by a correct diagnosis.
Ballotta et al2 are completely right when they claim that invasive CA carries a risk of complications (stroke, allergic reaction to contrast material, and local vascular complications) ranging between 0.5% and 4%.1,8,9
Thus preoperative diagnosis of carotid stenoses is still trapped in the dilemma between the inaccuracy of DUS (which therefore cannot be the stand-alone method for therapy decisions in every case for the reasons stated above) and the risk of complications inherent in invasive, but more objective, CA. Neither Qureshi et al nor Ballotta et al have considered that this diagnostic dilemma has already been solved by the advent of magnetic resonance angiography (MRA). This technique combines the benefits of DUS (noninvasive) and CA (objective, observer independent). Modern MRI systems combined with the appropriate investigation techniques provide excellent results compared with CA.10–12 A number of different authors have already claimed that MRA can largely replace CA.10–12 In this connection it must be stated that the results of MRA not only correlate closely with CA, but are actually superior in some cases given the asymmetry of carotid stenoses.13,14 Of course, we cannot ignore the fact here that different MRA techniques can provide different results.15 It is important to use MRA techniques with a high spatial resolution. MRA is an objective method because we must assume that an observer will not deliberately use a poor MRA technique. It is simple to recognize cases in which inadequate MRA technique has been used out of ignorance. The underlying parameters such as spatial resolution are recorded on the MRA films and can thus easily be identified, even by the most casual observer. Moreover, at the same workup, magnetic resonance provides optimal tomographic diagnostics of the cerebral parenchyma. This avoids the need for additional preoperative CT or MRI scans. The total acquisition time for a high-resolution MRI workup of the carotids and MRI imaging of the cerebrum is 20 to 30 minutes, which is more than acceptable.
Thus, MRA has already signposted the way out of the DUS-versus-CA dilemma in preoperative and preinterventional diagnostics of carotid stenoses. The combination of DUS and MRA makes possible optimal, noninvasive carotid diagnosis. CA can then be restricted to a few selected cases, eg, when DUS and MRA yield different results. However, these cases will most likely confirm the opinion of those authors who claim that the excellent DUS results provided under study conditions cannot be reproduced in general practice.
References
1. Qureshi AI, Suri MF, Ali Z, Kim SH, Fessler RD, Ringer AJ, Guterman LR, Budny JL, Hopkins LN. Role of conventional angiography in evaluation of patients with carotid artery stenosis demonstrated by Doppler ultrasound in general practice. Stroke. 2001; 32: 2287–2291.
2. Ballotta E, Da Giau G, Baracchini C. An unjustified return to the past. Stroke. 2002; 33: 879–881.
3. Ballotta E, Da Giau G, Abbruzzese E, Saladini M, Renon L, Scannapieco G, Meneghetti G. Carotid endarterectomy without angiography: can clinical evaluation and duplex ultrasonographic scanning alone replace traditional arteriography for carotid surgery workup? A prospective study. Surgery. 1999; 126: 20–27.[CrossRef][Medline] [Order article via Infotrieve]
4. Golledge J, Wright R, Pugh N, Lane IF. Colour-coded duplex assessment alone before carotid endarterectomy. Br J Surg. 1996; 83: 1234–1247.[CrossRef][Medline] [Order article via Infotrieve]
5. Johnston DC, Goldstein LB. Clinical carotid endarterectomy decision making: noninvasive vascular imaging versus angiography. Neurology. 2001; 56: 1009–1015.
6. Horrow MM, Stassi J, Shurman A, Brody JD, Kirby CL, Rosenberg HK. The limitations of carotid sonography: interpretive and technology-related errors. AJR Am J Roentgenol. 2000; 174: 189–194.
7. Dippel DW, de Kinkelder A, Bakker SL, van Kooten F, van Overhagen H, Koudstaal PJ. The diagnostic value of colour duplex ultrasound for symptomatic carotid stenosis in clinical practice. Neuroradiology. 1999; 41: 1–8.[CrossRef][Medline] [Order article via Infotrieve]
8. Dawson DL, Zierler RE, Strandness DE Jr, Clowes AW, Kohler TR. The role of duplex scanning and arteriography before carotid endarterectomy: a prospective study. J Vasc Surg. 1993; 18: 673–680.[CrossRef][Medline] [Order article via Infotrieve]
9. Dion JE, Gates PC, Fox AJ, Barnett HJ, Blom RJ. Clinical events following neuroangiography: a prospective study. Stroke. 1987; 18: 997–1004.
10. Randoux B, Marro B, Koskas F, Duyme M, Sahel M, Zouaoui A, Marsault C. Carotid artery stenosis: prospective comparison of CT, three-dimensional gadolinium-enhanced MR, and conventional angiography. Radiology. 2001; 220: 179–185.
11. Huston J III, Fain SB, Wald JT, Luetmer PH, Rydberg CH, Covarrubias DJ, Riederer SJ, Bernstein MA, Brown RD, Meyer FB, Bower TC, Schleck CD. Carotid artery: elliptic centric contrast-enhanced MR angiography compared with conventional angiography. Radiology. 2001; 218: 138–143.
12. Wutke R, Lang W, Fellner C, Janka R, Denzel C, Lell M, Bautz W, Fellner FA. High-resolution contrast-enhanced MR angiography with elliptic-centric k-space ordering of supra-aortic arteries in comparison with selective x-ray angiography. Stroke. 2002; 33: 1522–1529.
13. Elgersma OE, Wust AF, Buijs PC, van Der Graaf Y, Eikelboom BC, Mali WP. Multidirectional depiction of internal carotid arterial stenosis: three-dimensional time-of-flight MR angiography versus rotational and conventional digital subtraction angiography. Radiology. 2000; 216: 511–516.
14. Fellner FA, Wutke R, Lang W. Imaging of internal carotid arterial stenosis: is the new standard noninvasive? Radiology. 2001; 219: 858–859.
15. Fellner FA. Different MR angiography techniques provide different results in assessing extracranial carotid artery disease. AJR Am J Roentgenol. 2001; 177: 468–469.
Response
Department of Neurosurgery, Millard Fillmore Hospital, Department of Neurosurgery and Toshiba Stroke Research Center, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, New York
We read the letter from Drs Fellner and Lang with great interest. We certainly agree that medical professionals involved in the management of patients with carotid stenosis are faced with a dilemma. Physicians want a high degree of certainty regarding the diagnosis and severity of carotid stenosis. However, they want to avoid invasive testing such as contrast angiography that carries inherent risks. Unfortunately, an ideal situation does not exist at present. The noninvasive nature and low cost of carotid Doppler ultrasound would make it an ideal diagnostic modality for patients with carotid stenosis. However, in general practice, the inaccuracy of Doppler ultrasound makes it relatively unreliable for making decisions regarding the appropriateness of carotid endarterectomy.1,2 Drs Fellner and Lang have provided a valuable concept of using magnetic resonance angiography (MRA) to confirm the severity of stenosis in patients with carotid stenosis demonstrated by Doppler ultrasound. With recent developments in image acquisition and reconstruction,3 MRA definitely has the potential to replace contrast angiography for the assessment of patients with carotid stenosis before decisions are made regarding carotid endarterectomy. Johnston and Goldstein2 reported the misclassification rates of carotid Doppler ultrasound and MRA in 569 consecutive patients undergoing conventional angiography. Patients were classified as to whether carotid endarterectomy was indicated on the basis of the findings of each study. Overall, the misclassification rate was higher for Doppler ultrasound (28%) than for MRA (18%). Both imaging studies were performed in 11% of the 569 patients. The results of the two tests were concordant for assessment of the degree of carotid stenosis in 40 cases. When the results were concordant, the misclassification rate for the combination of Doppler ultrasound and MRA was lower than that for either test used independently (8% misclassification rate).
Using a combination of Doppler ultrasound and MRA, patients can be classified into 2 groups, as follows: (1) patients with moderate to severe stenosis demonstrated on both modalities and (2) patients with moderate to severe stenosis visualized on one modality but not confirmed by the other modality. It needs to be determined whether the accuracy of MRA justifies denying the second group of patients any further diagnostic tests or revascularization therapy or these patients should undergo contrast angiography for further characterization of lesion. Nonetheless, a certain proportion of patients in whom there is good agreement between Doppler ultrasound and MRA may not require contrast angiography. The exact proportion of these patients may be variable in different settings depending on the performance of carotid Doppler ultrasound and MRA. The methodology proposed by Drs Fellner and Lang appears to have merit and deserves evaluation in future studies.
References
1. Qureshi AI, Suri MFK, Ali Z, Kim SH, Fessler RD, Ringer AJ, Guterman LR, Budny JL, Hopkins LN. Role of conventional angiography in evaluation of patients with carotid artery stenosis demonstrated by Doppler ultrasound in general practice. Stroke. 2001; 32: 2287–2291.
2. Johnston DC, Goldstein LB. Clinical carotid endarterectomy decision making: noninvasive vascular imaging versus angiography. Neurology. 2001; 56: 1009–1015.
3. Elgersma OE, Wust AF, Buijs PC, van Der Graaf Y, Eikelboom BC, Mali WP. Multidirectional depiction of internal carotid arterial stenosis: three-dimensional time-of-flight angiography versus rotational and conventional digital subtraction angiography. Radiology. 2000; 216: 511–516.
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