Annals of Vascular Surgery
Volume 23, Issue 2 , Pages 186-193, March 2009

Multidetector-Row Computed Tomography in Evaluation of Atherosclerotic Carotid Plaques Complicated with Intraplaque Hemorrhage

  • Marko Ajduk

      Affiliations

    • Department of Vascular Surgery, University Hospital Dubrava, Zagreb, Croatia
    • Corresponding Author InformationCorrespondence to: Marko Ajduk, MD, Department of Vascular Surgery, University Hospital Dubrava, Av. Gojka Šuška 6, 10000 Zagreb, Croatia
    • ,
  • Ladislav Pavić

      Affiliations

    • Department of Radiology, University Hospital Dubrava, Zagreb, Croatia
    • ,
  • Stela Bulimbašić

      Affiliations

    • Depatment of Pathology, University Hospital Dubrava, Zagreb, Croatia
    • ,
  • Mirko Šarlija

      Affiliations

    • Department of Vascular Surgery, University Hospital Dubrava, Zagreb, Croatia
    • ,
  • Predrag Pavić

      Affiliations

    • Department of Vascular Surgery, University Hospital Dubrava, Zagreb, Croatia
    • ,
  • Leonardo Patrlj

      Affiliations

    • Department of Vascular Surgery, University Hospital Dubrava, Zagreb, Croatia
    • ,
  • Boris Brkljačić

      Affiliations

    • Department of Radiology, University Hospital Dubrava, Zagreb, Croatia

published online 28 July 2008.

Article Outline

Our aim was to determine the sensitivity and specificity of multidetector-row computed tomography (CT) in detecting atherosclerotic carotid plaques complicated with intraplaque hemorrhage. We examined carotid plaques from 31 patients operated for carotid artery stenosis. Results of preoperative multidetector-row CT analysis of carotid plaques were compared with results of histological analysis of the same plaque areas. Carotid endarterectomy was performed within 1 week of multidetector-row CT. American Heart Association classification of atherosclerotic plaques was applied for histological classification. Median tissue density of carotid plaques complicated with intraplaque hemorrhage was 22 Hounsfield units (HU). Median tissue density of noncalcified segments of uncomplicated plaques was 59 HU (p = 0.0062). The highest tissue density observed for complicated plaques was 31 HU. Multidetector-row CT detected plaques complicated with hemorrhage with sensitivity of 100% and specificity of 64.7%, with tissue density of 31 HU as a threshold value. Multidetector-row CT showed a high level of sensitivity and a moderate level of specificity in detecting atherosclerotic carotid plaques complicated with hemorrhage.

 

Back to Article Outline

Introduction 

Large randomized controlled trials demonstrated benefit of carotid endarterectomy (CEA) in symptomatic patients with high-degree carotid artery stenosis.1, 2 Asymptomatic patients benefit less from CEA, with absolute risk reduction of only about 1% annually during 5-year follow-up.3, 4 Therefore, a large number of asymptomatic patients must be operated to prevent a small number of neurological events. The total number of operated asymptomatic patients may be lowered if subgroups of asymptomatic patients who benefit most from CEA could be identified. Several studies have shown a higher incidence of neurological incidents in patients with so-called soft plaques (plaques predominantly consisting of lipids, tissue debris, and hemorrhage).5, 6, 7, 8, 9, 10 Ultrasound analysis of carotid plaques demonstrated that hypoechoic plaques represent an independent risk factor for stroke incidence in adults aged 65 years or older.11 Takaya et al.12 followed asymptomatic patients for 38 months and showed that patients with intraplaque hemorrhage on initial magnetic resonance imaging (MRI) had a 5.2 times higher incidence of cerebrovascular events. The American Heart Association (AHA) classification of atherosclerotic plaques defines eight types of plaques, according to histological content (Table I).13, 14 Atherosclerotic carotid plaques complicated with intraplaque hemorrhage (AHA type VIb) are considered unstable and are associated with a higher incidence of cerebrovascular events.12, 15, 16, 17 Computed tomographic (CT) angiography demonstrated high accuracy in diagnosing carotid artery stenosis.18, 19, 20, 21, 22 An additional feature of CT is its ability to measure tissue density (expressed as number of Hounsfield units [HU]). Thus, it can provide some information about the type of analyzed tissue. Atherosclerotic carotid plaques with lower tissue density on multidetector-row CT (MDCT) are associated with a lower incidence of cerebrovascular events.6, 7 While single slice CT showed conflicting results in determining carotid plaque composition, MDCT showed good correlation of findings with histological analysis of coronary plaques.23, 24, 25, 26, 27 Histological analysis of coronary plaques showed that remodeling of atherosclerotic plaque changes its histological content. Therefore, the period between imaging and histological analysis should be as short as possible.28 We compared results of MDCT and histological analysis and calculated sensitivity and specificity of MDCT in detection of AHA type VIb atherosclerotic carotid plaques (plaques complicated with intraplaque hemorrhage, most often containing a mixture of lipids, hemorrhage, and necrotic debris). CEA was performed within 1 week of MDCT.

Table I. AHA classification of atherosclerotic plaques8, 9
AHA classificationDescription
IScattered macrophage foam cells
IILayers of macrophage foam cells and lipid-laden smooth muscle cells—fatty streaks
IIIType II with extracellular lipid droplets
IVConfluent extracellular lipid core
VLipid core and thick layer of fibrous connective tissue (previously Va, also called “multilayered fibroatheroma”)
VITypes IV or V with disruption of the lesion surface (VIa), hematoma or hemorrhage (VIb), or thrombosis (VIc)
VIILargely calcified plaque (previously Vb)
VIIIConsists mainly of fibrous connective tissue and little or no accumulated lipid or calcium (previously Vc)

Back to Article Outline

Materials and Methods 

Carotid plaques from 31 consecutive patients operated for carotid artery stenosis were included in this prospective study. There were 21 male and 10 female patients, aged 51-87, median 70, years. There were six symptomatic and 25 asymptomatic patients (Table II). Patients who experienced cerebral insult, transient ischemic attack, or amaurosis fugax on the side of the affected carotid artery within 6 months of MDCT were considered symptomatic.

Table II. Patient characteristics, MDCT, histological findings, and duplex findings
PatientAge (years)GenderSymptomsStenosis (%, MDCT)Tissue density (HU)AHA plaque typeStenosis (%, duplex)
167MNo7059VII65
274MNo95−11.6VIb90
365MNo95−17.6VIb95
456MNo9562.6V95
587MNo90−23.6V90
677MNo9063V90
770MNo9062.8V90
877MNo9022.2VIb90
982FYes8031.2VIb85
1080MNo7018.2VIb70
1162MYes8022.4V75
1281MYes9028.5VIb90
1368MNo8062.8V70
1477MNo9525.2VIb75
1568FNo7060.7V65
1679MNo9024.1VIb70
1761MNo8014.7VIb65
1868MNo8021.7VIb70
1977MNo8017.7V80
2072MYes9023.3VIb80
2165MNo8042.1V95
2264MNo9526.8VIb95
2361FNo906.7V80
2476FYes80131VII70
2559FYes95−3VIb80
2676FNo90150V80
2767FNo90−4.0VIb90
2864FNo7028.6V75
2951FNo8035.8VIII70
3080FNo9011.6V95
3172MNo7059.8V75
SummaryMedian 70, range 51-87M, 21; F, 10Yes 6 No 25Mean 84.8 ± 8.6Plaque typeMedianRangeVIb, 14; other, 17Mean 80.8 ± 10.3
VIb22−17 to 31
Other59−6 to 150

Indications for CEA were symptomatic patients with carotid artery stenosis >60% and asymptomatic patients with stenosis >70%. All patients had the same imaging evaluation: color duplex Doppler first, and MDCT in patients with carotid stenosis >60% on Doppler.

Endarterectomy was performed within 1 week of MDCT evaluation. Approval from the institutional ethical committee was obtained.

Two experienced radiologists performed Doppler examination, using the Logiq 9 scanner, with 7-9 and 9-14 MHz probes (GE Healthcare, Milwaukee, WI).

MDCT Analysis 

The Siemens (Erlangen, Germany) Somatom Sensation 16-row MDCT scanner was used. One radiologist evaluated data on a Siemens Leonardo Syngo2004A workstation. The standardized optimized, contrast-enhanced protocol was used with intermediate reconstruction: 120 kVp, 120 mAs, collimation 16 x 0.75 mm, pitch 1, slice thickness 0.75 mm. Iopamidol was used as contrast medium (370 mg iodine/mL, 4 mL/sec, 70 mm3, 325 psi). Transversal multiplanar reconstructions, orthogonal to the vessel long axis in both coronal and sagittal planes, were used for plaque analysis. Three measurements of tissue density were performed on the visually least dense area of plaque at the level of maximal stenosis. Measurements were performed on a 2 mm2 circular area and the smallest value was recorded (Fig. 1, Fig. 2). Calcifications are obvious on MDCT and were not further analyzed. The distance between carotid bifurcation and level of maximal stenosis was recorded in order to help the pathologist find the corresponding level for histological analysis. Percentage of stenosis was calculated applying North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria.14

Surgical Technique 

Patients underwent CEA under locoregional or general anesthesia, with selective use of intraluminal shunt in the former group of patients and in all patients in the latter group. Four patients were operated under general anesthesia. Two of them had concomitant cardiac surgery, one had a history of epileptic seizures, and one patient with contralateral occlusion had an explicit wish for general anesthesia. Care was taken to preserve the morphological integrity of plaques as much as possible. There were no verified perioperative insults. The patient with contralateral carotid occlusion had transient postoperative weakness of the contralateral hand without CT evidence of ischemic brain lesion.

Histological Analysis 

Immediately after CEA, plaques were formalin-fixed (10% buffered formaldehyde) and sent for histological analysis. One pathologist, blinded for MDCT plaque density, performed histological analysis. If calcifications were extensive, plaques were first decalcified using 20% nitric acid. That procedure eliminates calcifications while preserving remaining histological content. Samples were sliced in a serial manner, starting from the bifurcation, followed by sections 2 mm apart toward the internal carotid artery. The serial section technique assured precise measurement of the distance between the bifurcation and the level of maximal stenosis.

Plaque sections were embedded in paraffin and cut in 4-μm-thin slices, using the standard process. Slices were stained with hematoxylin and with Mallory trichrome if necessary (Fig. 3, Fig. 4). One pathologist examined all plaques and classified them according to the AHA classification of atherosclerotic plaques. The radiologist who performed MDCT analysis was involved in histological analysis, to make sure that the same plaque areas were analyzed on MDCT and histology.

Data Analysis 

The difference of median tissue density between AHA type VIb plaques and other plaque types was calculated using the Mann-Whitney U-test. p < 0.05 was considered statistically significant. To determine the cut-off value of tissue density, receiver operating characteristic (ROC) analysis was used.

Back to Article Outline

Results 

There were 14 (45%) AHA VIb plaques and 17 (55%) plaques of other AHA types (V, VII, and VIII). Median MDCT tissue density of type VIb plaques was 22 HU (range –17 to 31), and median tissue density of noncalcified segments of noncomplicated plaques was 59 HU (range –6 to 150) (p = 0.0062, Mann-Whitney U-test) (Fig. 5). ROC analysis showed 100% sensitivity and 64.7% specificity of MDCT in detecting plaques complicated with intraplaque hemorrhage, with tissue density of 31 HU as a threshold value (i.e., no plaque with MDCT tissue density over 31 HU was complicated with intraplaque hemorrhage) (Fig. 6). Four of six plaques from symptomatic patients were AHA type VIb, and 10 of 25 plaques from asymptomatic patients were AHA type VIb.

Back to Article Outline

Discussion 

This study showed that MDCT could detect atherosclerotic carotid plaque complicated with hemorrhage with 100% sensitivity, with tissue density of 31 HU as a threshold value. Previous studies showed inconclusive results regarding the accuracy of single-slice CT in analyzing plaque composition.23, 24 De Weert et al.29 showed good correlation between in vivo MDCT findings and histological findings; however, in their analysis of 15 carotid plaques, the period between MDCT evaluation and endarterectomy was up to 3 months. During that period, remodeling of plaques could change their histological appearance. Histological analysis of coronary plaques performed within 1 week after infarction showed morphological features of instability, while plaques taken later were histologically similar to those in patients with stable angina.28 To minimize inaccuracy resulting from this fact, all patients in this study were operated within 1 week of MDCT analysis.

To our knowledge, among studies comparing in vivo MDCT and histological analysis of carotid plaques and providing the period between MDCT and endarterectomy of less than 1 week, this study enrolled the largest number of patients.

Our aim was to identify plaques with intraplaque hemorrhage (AHA type VIb) using MDCT. Carotid plaques are most often heterogeneous, and small areas of plaque often have mixed histological content. Lipids, hemorrhage, and necrotic debris (“soft tissue”) have the lowest tissue density on MDCT, and other tissue components (fibrosis or calcifications) increase tissue density. This can influence MDCT results by giving higher tissue density values even in predominantly soft areas of plaque due to the partial volume effect. A similar effect is produced by contrast medium in vessel lumen and calcified portions of the plaque. To minimize the influence of this effect, we performed three measurements per slice on the chosen plaque area (visually least dense area) and recorded only the smallest value since no plaque component has lower tissue density than lipids, hemorrhage, or necrotic debris.

With a 2 mm2 area on which tissue density was measured and 0.75 mm slice thickness, 1.5 mm3 of tissue volume was measured by each measurement. Even plaques with such a small MDCT detectable amount of soft tissue (which is most often a combination of lipids, hemorrhage, and necrotic debris) should be regarded as potentially vulnerable since it is impossible to tell by MDCT whether hemorrhage within plaque is expanding or reducing due to plaque remodeling. To provide the same plaque level for MDCT and histological analysis, we measured the distance from the bifurcation to the level of maximal stenosis on MDCT, and that value was used by the pathologist to find the corresponding level of specimen for histological analysis. It might have happened that a minor degree of longitudinal plaque shrinkage occurred during the histological processing, but it is unlikely to be significant because of the low overall water content of plaques. However, serial slicing and embedding of the whole plaque (including the planes below and above the MDCT-measured level of maximal stenosis) and the possibility of additional slices from deeper levels of paraffin-embedded material assure that the level of the narrowest lumen (maximal stenosis) had been chosen for the analysis.

Current clinical practice in the treatment of asymptomatic patients with carotid artery stenosis differs among different countries and even among different institutions within the same country.30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43 In general, asymptomatic patients with carotid artery stenosis are treated more conservatively in Europe than in the United States. Asymptomatic patients with carotid artery stenosis comprise 11-52% and 37-92% of all patients operated for carotid artery stenosis in Europe and the United States, respectively.30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43 Several authors have indicated that operative treatment of asymptomatic patients with carotid artery stenosis should be considered only for medically stable patients with ≥80% stenosis with life expectancy of at least 5 years and only if a <3% perioperative complication rate can be achieved.44, 45 Asymptomatic patients with complicated plaque and <80% carotid artery stenosis, who would not be treated if the above-mentioned recommendations are applied, could benefit from a diagnostic method that is able to detect some features of carotid plaque associated with increased risk of a cerebrovascular event. Asymptomatic patients with carotid artery stenosis of <80% and uncomplicated plaque probabaly require only the best medical therapy.44, 45, 46, 47 The decisions as to which diagnostic method to use and when to treat asymptomatic patients are affected not only by the results of large trials but also by diagnostic resources available, medical system funds, and the possibility of treating patients with carotid artery stenosis with low morbidity and mortality at a particular institution. MDCT increases the cost of diagnostic evaluation for each patient if compared to duplex analysis alone and exposes patients to radiation. However, MDCT is noninvasive and accurate in diagnosing carotid artery stenosis.18, 19, 20, 21, 22 Furthermore, MDCT showed very good interobserver agreement in the evaluation of degree of carotid artery stenosis and can also provide information about the type of analyzed tissue and the presence of intracranial arterial stenosis.18, 19, 20, 21, 22, 29, 48, 49 Studies dealing with Doppler examination of carotid artery stenosis showed marked interobserver variabilities.50, 51, 52 Several studies based on measurement of gray-scale median of carotid plaques showed conflicting results regarding the correlation of findings with histological content, while studies based on visual evaluation of ultrasound findings showed high variability of intra- and interobserver agreement.53 In our view, duplex and MDCT are complementary studies. We perform duplex examination first, followed by MDCT, if >60% carotid artery stenosis is found on duplex. We believe that the higher cost of diagnostic evaluation that includes MDCT could be in part compensated by the potential reduction of the number of operated asymptomatic patients.

Back to Article Outline

Conclusion 

MDCT showed a very high level of sensitivity and a moderate level of specificity in detecting hemorrhage within atherosclerotic carotid plaque. Plaques with tissue density over 31 HU on MDCT were not complicated with intraplaque hemorrhage. Technical advancements of CT equipment may probably increase the specificity of the method.

Back to Article Outline

References 

  1. North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. N Engl. J Med. 1991;325:445
  2. European Carotid Surgery Trialist's Collaborative Group. Medical Research Council European Carotid Surgery Trial. Interim results for symptomatic patients with severe (70-99%) or with mild (0-29%) carotid stenosis. Lancet. 1991;337:1235
  3. Executive Committee for the Asymptomatic Carotid Atherosclerosis Study. Endarterectomy for asymptomatic carotid artery stenosis. JAMA. 1995;273:1421–1428
  4. Halliday A, Mansfield A, Marro J, et al. Asymptomatic Carotid Surgery Trial (ACST) Collaborative Group. Prevention of disabling and fatal strokes by successful carotid endarterectomy in patients without recent neurological symptoms: randomised controlled trial. Lancet. 2004;363:1491–1502
  5. Grønholdt MLM, Nordestgaard BG, Schroeder TV, et al. Ultrasonic echolucent carotid plaques predict future strokes. Circulation. 2001;104:68–73
  6. Serfaty JM, Nonent M, Nighoghossian N, et al. for the CARMEDAS Study Group. Plaque density on CT, a potential marker of ischemic stroke. Neurology. 2006;66:118–120
  7. Nandalur KR, Baskur E, Hagspiel KD, et al. Calcified carotid atherosclerotic plaque is associated less with ischemic symptoms than is noncalcified plaque on MDCT. AJR Am J Roentgenol. 2005;184:295–298
  8. European Carotid Plaque Study Group . Carotid artery plaque composition—relationship to clinical presentation and ultrasound B-mode imaging. Eur J Vasc Endovasc Surg. 1995;10:23–30
  9. Carra G, Visona A, Bonanome A, et al. Carotid plaque morphology and cerebrovascular events. Int Angiol. 2003;22:284–289
  10. Mathiesen EB, Bonaa KH, Joakimsen O. Echolucent plaques are associated with high risk of ischemic cerebrovascular events in carotid stenosis: the Tromso Study. Circulation. 2001;103:2171–2175
  11. Polak JF, Shemanski L, O'Leary DH, et al. Hypoechoic plaque at US of the carotid artery: an independent risk factor for incident stroke in adults aged 65 years or older. Cardiovascular Health Study. Radiology. 1998;208:649–654
  12. Takaya N, Yuan C, Chu B, et al. Association between carotid plaque characteristics and subsequent ischemic cerebrovascular events: a prospective assessment with MRI—initial results. Stroke. 2006;37:818–823
  13. Stary HC, Chandler AB, Dinsmore R, et al. A definition of advanced types of atherosclerotic lesions and a histological classification of atherosclerosis: a report from the Committee on Vascular Lesions of the Council an Arteriosclerosis, American Heart Association. Circulation. 1995;92:1355–1374
  14. Stary HC. Natural history and histological classification of atherosclerotic lesions: an update. Arterioscler Thromb Vasc Biol. 2000;20:1177–1178
  15. Rao DS, Goldin JG, Fishbein MC. Determinants of plaque instability in atherosclerotic vascular disease. Cardiovasc Pathol. 2005;14:285–293
  16. Mofidi R, Crotty TB, McCarthy P, et al. Association between plaque instability, angiogenesis and symptomatic carotid occlusive disease. Br J Surg. 2001;88:945–950
  17. Imparato AM, Riles TS, Mintzer R, et al. The importance of hemorrhage in the relationship between gross morphologic characteristics and cerebral symptoms in 376 carotid artery plaques. Ann Surg. 1983;197:195–203
  18. Josephson SA, Bryant SO, Mak HK, et al. Evaluation of carotid stenosis using CT angiography in the initial evaluation of stroke and TIA. Neurology. 2004;63:457–460
  19. Chen CJ, Lee TH, Hsu HL, et al. Multi-slice CT angiography in diagnosing total versus near occlusions of the internal carotid artery: comparison with catheter angiography. Stroke. 2004;35:83–85
  20. Koelemay MJW, Nederkoorn PJ, Reitsma JB, et al. Systematic review of computed tomographic angiography for assessment of carotid artery disease. Stroke. 2004;35:2306–2312
  21. Moll R, Dinkel HP. Value of the CT angiography in the diagnosis of common carotid artery bifurcation disease: CT angiography versus digital subtraction angiography and color flow Doppler. Eur J Radiol. 2001;39:155–162
  22. Ibarra-de Grassa B, Romero-Vidal FJ, Munoz-Martinez V. Usefulness of arteriography with multislice spiral computed tomography in the diagnosis of preocclusive stenosis of the cervical internal carotid artery. Rev Neurol. 2003;37:632–636
  23. Walker LJ, Ismail A, McMeekin W, et al. Computed tomography angiography for the evaluation of carotid atherosclerotic plaque: correlation with histopathology of endarterectomy specimens. Stroke. 2002;33:977–981
  24. Estes JM, Quist WC, Lo Gerfo FW, et al. Noninvasive characterization of plaque morphology using helical computed tomography. J. Cardiovasc. Surg. (Torino). 1998;39:527–534
  25. Oliver TB, Lammie GA, Wright AR, et al. Atherosclerotic plaque at the carotid bifurcation: CT angiographic appearance with histopathologic correlation. AJNR Am J Neuroradiol. 1999;20:897–901
  26. Schroeder S, Kuettner A, Leitritz M, et al. Reliability of differentiating human coronary plaque morphology using contrast-enhanced multislice spiral computed tomography: a comparison with histology. J Comput Assist Tomogr. 2004;28:449–454
  27. Schroeder S, Kopp AF, Baumbach A, et al. Noninvasive detection and evaluation of atherosclerotic coronary plaques with multislice computed tomography. J Am Coll Cardiol. 2001;37:1430–1435
  28. Depre C, Wijns W, Robert AM, et al. Pathology of unstable plaque: correlation with the clinical severity of acute coronary syndromes. J Am Coll Cardiol. 1997;30:694–702
  29. De Weert TT, Ouhlous M, Meijering E, et al. In vivo characterization and quantification of atherosclerotic carotid plaque components with multidetector computed tomography and histopathological correlation. Arterioscler Thromb Vasc Biol. 2006;26:2366–2372
  30. McPhee JT, Hill JS, Ciocca RG, Messina LM, Eslami MH. Carotid endarterectomy was performed with lower stroke and death rates than carotid artery stenting in the United States in 2003 and 2004. J Vasc Surg. 2007;46:1112–1118
  31. Kragsterman B, Björck M, Lindbäck J, Bergqvist D, Pärsson H on behalf of the Swedish Vascular Registry (Swedvasc). Long-term survival after carotid endarterectomy for asymptomatic stenosis. Stroke. 2006;37:2886–2891
  32. Šoša T, Ajduk M, Erdelez L, Škopljanac A. Carotid surgery 2004. State of the art, prognosis and perspective. Acta Clin. Croatica. 2004;43(Suppl. 1):106–117
  33. Mayo SW, Eldrup-Jorgensen J, Lucas FL, Wennberg DE, Bredenberg CE. Carotid endarterectomy after NASCET and ACAS: a statewide study. J Vasc Surg. 1998;27:1017–1023
  34. Long GW, Nuthakki V, Bove PG, et al. Contemporary outcomes for carotid endarterectomy at a large community-based academic health center. Ann Vasc Surg. 2007;21:321–327
  35. LaMuraglia GM, Brewster DC, Moncure AC, et al. Carotid endarterectomy at the millennium: what interventional therapy must match. Ann Surg. 2004;240:535–544
  36. Mehta RH, Zahn R, Hochadel M, et al. Comparison of in-hospital outcomes of patients with versus without previous carotid endarterectomy undergoing carotid stenting (from the German ALKK CAS Registry). Am J Cardiol. 2007;99:1288–1293
  37. Smurawska LT, Bowyer B, Rowed D, Maggisano R, Oh P, Norris JW. Changing practice and costs of carotid endarterectomy in Toronto, Canada. Stroke. 1998;29:2014–2017
  38. Karp HR, Flanders WD, Shipp CC, Taylor B, Martin D. Carotid endarterectomy among Medicare beneficiaries: a statewide evaluation of appropriateness and outcome. Stroke. 1998;29:46–52
  39. Setacci C, Chisci E, de Donato G, Setacci F, Galzerano G. Carotid artery stenting in a single center: are six years of experience enough to achieve the standard of care?. Eur J Vasc Endovasc Surg. 2007;34:655–662
  40. Rodgers H, Oliver SE, Dobson R, Thomson RG. on behalf of the Northern Regional Carotid Endarterectomy Audit Group. A regional collaborative audit of the practice and outcome of carotid endarterectomy in the United Kingdom. Eur J Vasc Endovasc Surg. 2000;19:362–369
  41. Wong JH, Lubkey TB, Suarez-Almazor ME, Findlay JM. Improving the appropriateness of carotid endarterectomy: results of a prospective city-wide audit. Stroke. 1999;30:12–15
  42. Cebul RD, Snow RJ, Pine R, Hertzer NR, Norris DG. Indications, outcomes and provider volumes for carotid endarterectomy. JAMA. 1998;279:1282–1287
  43. Melissano G, Castellano R, Mazzitelli S, Zoppei G, Chiesa R. Safe and cost-effective approach to carotid surgery. Eur J Vasc Endovasc Surg. 1997;14:164–169
  44. Dodick DW, Meissner I, Meyer FB, Cloft HJ. Evaluation and management of asymptomatic carotid artery stenosis. Mayo Clin Proc. 2004;79:937–944
  45. Rockman CB, Riles TS, Lamparello PJ, et al. Natural history and management of the asymptomatic, moderately stenotic internal carotid artery. J Vasc Surg. 1997;25:423–431
  46. European Carotid Surgery Trialists' Collaborative Group. Risk of stroke in the distribution of an asymptomatic carotid artery. Lancet. 1995;345:209–212
  47. CASANOVA Study Group . Carotid surgery versus medical therapy in asymptomatic carotid stenosis. Stroke. 1991;22:1229–1235
  48. Saba L, Mallarini G. MDCTA of carotid plaque degree of stenosis: evaluation of interobserver agreement. AJR Am J Roentgenol. 2008;190:W41–W46
  49. Schuknecht B. High-concentration contrast media (HCCM) in CT angiography of the carotid system: impact on therapeutic decision making. Neuroradiology. 2007;49(Suppl. 1):S15–S26
  50. Jahromi AS, Cinà CS, Liu Y, Clase CM. Sensitivity and specificity of color duplex ultrasound measurement in the estimation of internal carotid artery stenosis: a systematic review and meta-analysis. J Vasc Surg. 2005;41:962–972
  51. Mikkonen RH, Kreula JM, Virkkunen PJ. Reproducibility of Doppler ultrasound measurements. Acta Radiol. 1996;37:545–550
  52. Henry-Feugeas M, Alkilic-Genauzeau I, Aymé N, Schouman-Claeys E. Variability of ultrasonography velocity assessment of the carotid arteries. J Radiol. 2000;81:445–449
  53. Sztajzel R. Ultrasonographic assessment of the morphological characteristics of the carotid plaque. Swiss Med. Wkly. 2005;135:635–643

PII: S0890-5096(08)00201-X

doi:10.1016/j.avsg.2008.05.008

Annals of Vascular Surgery
Volume 23, Issue 2 , Pages 186-193, March 2009

Article Tools

* Image Usage & Resolution