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ARTICLES: James Kennedy, Hude Quan, William A. Ghali, and Thomas E. Feasby Importance of the imaging modality in decision making about carotid endarterectomy Neurology 2004; 62: 901-904 [Abstract] [Full text] [PDF]

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Reply to Hoggard

Thomas E. Feasby, James Kennedy, Hude Quan, William A. Ghali   (17 May 2004)

Importance of the imaging modality in decision making about carotid endarterectomy

N. Hoggard   (17 May 2004)

Reply to Hoggard 17 May 2004
Thomas E. Feasby, University of Alberta, Canada , James Kennedy, Hude Quan, William A. Ghali Send Correspondence to journal: Re: Reply to Hoggard tomfeasby{at}cha.ab.ca Thomas E. Feasby, et al.	We thank Dr Hoggard for his comments and agree that with all imaging strategies, conventional catheter angiography has limitations in the assessment of carotid stenosis. However, we maintain that it is still the gold standard in the decision-making process to perform carotid endarterectomy due to its use in the major randomized controlled trials. We agree that the non-invasive imaging technologies, MR angiography and CT angiography, are still evolving and it was with this in mind that the current study was performed. We specifically chose to compare the various non-invasive strategies (single or dual modality, and their potential outcomes) with the (historical) gold standard of conventional catheter angiography because the former more accurately reflect contemporary practice. The panel’s ratings reflected that the imaging literature has not kept pace with these technologies, especially where there was disagreement among the panel members. Areas of future study were identified, particularly where an person’s capacity to benefit from carotid endarterectomy is marginal. For instance, the optimal imaging strategy in those with moderate symptomatic stenosis. We are not advocating a step backwards to the widespread use of conventional catheter angiography. As technology progresses, studies such as ours will need repeating to understand the place of new imaging techniques compared with older but perhaps outdated techniques, as they become accepted into contemporary practice. This study serves to remind physicians of the need for caution in the interpretation of imaging data when deciding whether to offer carotid endarterectomy appropriately to patients. A recent Neurology editorial relative to another study draws a similar conclusion. [8] References 5. Barnett, HJM, Taylor, DW, Eliasziw, M, et al. Benefit of carotid endarterectomy in patients with symptomatic moderate or severe stenosis. NEJM 1998;339:1415-1425. 6. ECST Collaborative Group. Randomised trial of endarterectomy for recently symptomatic carotid stenosis: Final results. Lancet 1998;351:1379-1387. 7. Executive committee for ACAS. Endarterectomy for asymptomatic carotid artery stenosis. JAMA 1995;273:1421-1428. 8. Powers WJ. Carotid arteriography: Still golden after all these years? Neurology 2004;62:1246-1247.
Importance of the imaging modality in decision making about carotid endarterectomy 17 May 2004
N. Hoggard, Manchester Neuroscience center, Hope Hospital, Salford. UK 1 Lyndhurst Road, Manchester, M20 3JU, UK Send Correspondence to journal: Re: Importance of the imaging modality in decision making about carotid endarterectomy kathy_pieper{at}urmc.rochester.edu N. Hoggard	I read with great interest the article by Kennedy et al [1] which stressed the importance of imaging modality in decision making about carotid endarterectomy. As the authors state, the source of information for the degree of internal carotid artery stenosis is crucial in making appropriate decisions. In their final paragraph, they choose to "make physicians aware" of the limitations of noninvasive imaging strategy. While we agree with their good advice and overall conclusions, they failed to point out some of the problems with interpretation of the imaging literature. Conventionally-performed catheter angiography is no longer a "gold" standard, as a comparative study with rotational angiography has previously shown. [2] The reasons why conventionally performed catheter angiography is not and has never been a good reference standard for evaluation of the cross sectional imaging based non-invasive techniques is explained in the article by Hirai et al. [3] Stenoses are not necessarily concentric and round but may be elliptical or even irregular. The luminal morphology of a stenosis is critical to its measurement and the fewer the two dimensional projectional images used, the greater the opportunity to miss the minimal diameter of, for example, an ellipse. Conventional catheter angiography underestimates the maximal luminal stenosis in compared to the rotational angiography. [2] If the same projections of MR angiograhy and convention catheter angiography are compared, then the over-estimation of stenoses by MR angiography has been shown not to arise. [4] The second major problem when interpretating the imaging literature is that it has not kept pace with the very rapid advance in technology that renders the majority of limited value. For example, most centers across North America and western european countries now have access to multislice CT. Also, the resolution provided by MR angiography continues to improve. Until there are studies that employ rotational angiography as the reference standard the true accuracy of state of the art multislice CT angiography, MR angiography and duplex ultrasound will remain unclear but their tendency to miss-classify and over estimate stenoses may in the future be differently evaluated in the light of such new comparison. References 1)Kennedy J, Quan H, Ghali WA, Feasby TE. Importance of the imaging modality in decision making about carotid endarterectomy. Neurology. 2004;62:901-4. 2)Elgersma OE, Buijs PC, Wust AF, van der Graaf Y, Eikelboom BC, Mali WP. Maximum internal carotid arterial stenosis: assessment with rotational angiography versus conventional intraarterial digital subtraction angiography. Radiology. 1999;213:777-83. 3)Hirai T, Korogi Y, Ono K, Murata Y, Takahashi M, Suginohara K, Uemura S. Maximum stenosis of extracranial internal carotid artery: effect of luminal morphology on stenosis measurement by using CT angiography and conventional DSA. Radiology. 2001;221:802-9. 4)Nederkoorn PJ, Elgersma OE, Mali WP, Eikelboom BC, Kappelle LJ, van der Graaf Y. Overestimation of carotid artery stenosis with magnetic resonance angiography compared with digital subtraction angiography. J Vasc Surg. 2002;36:806-13. Conflicts of interest: none.