Neuroradiology/Head and Neck Imaging Review

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1 Neuroradiology/Head and Neck Imaging Review Provenzale and Sarikaya MRI, MRA, and CTA in Diagnosis of Artery Dissection Neuroradiology/Head and Neck Imaging Review James M. Provenzale 1,2 Basar Sarikaya 1,3 Provenzale JM, Sarikaya B Keywords: carotid artery, CT angiography (CTA), dissection, MR angiography (MRA), MRI, vertebral artery DOI: /AJR Received August 16, 2008; accepted after revision March 20, Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC Address correspondence to J. M. Provenzale. 2 Department of Radiology, Emory University School of Medicine, Atlanta, GA. 3 Department of Radiology, Gaziosmanpasa University, Tokat, Turkey. AJR 2009; 193: X/09/ American Roentgen Ray Society Comparison of Test Performance Characteristics of MRI, MR Angiography, and CT Angiography in the Diagnosis of Carotid and Vertebral Artery Dissection: A Review of the Medical Literature OBJECTIVE. Initial assessment of patients with suspected dissection of the carotid or vertebral arteries typically is made by MRI, alone or in combination with MR angiography (MRA) or CT angiography (CTA). We reviewed the medical literature to determine, based on test performance characteristics such as sensitivity, specificity, positive predictive value, and negative predictive value, whether evidence could be found to support routine use of one imaging technique over the other for assessment of suspected dissection. CONCLUSION. Test characteristics for MR techniques such as MRI and MRA were relatively similar to those for CTA in diagnosis of carotid and vertebral artery dissection. D issection of the craniocervical arteries (i.e., the carotid and vertebral arteries), which was once considered an uncommon diagnosis, has become increasingly recognized as a cause of stroke in young and middleaged individuals. In part, this increased recognition is due to greater awareness that dissection is often spontaneous in nature, thus raising suspicion of this diagnosis in patients who have not sustained neck or head trauma [1]. In addition, increased use of noninvasive imaging studies has allowed larger numbers of patients to be screened who might not otherwise have undergone invasive digital subtraction angiography (DSA) (i.e., catheter angiography) for diagnosis. In some populations, the rate of dissection of the craniocervical arteries has been diagnosed at rates 3 10 times greater than that determined before the use of MRI, MR angiography (MRA), and, more recently CT angiography (CTA) studies both in patients with spontaneous dissections and in those who have experienced blunt neck trauma [2 4]. At this point, a number of studies comparing test performance characteristics of noninvasive studies against those of DSA have been published. The role of Doppler sonography in diagnosis of dissection is not reviewed here because it is less commonly used and because limitations have been noted by multiple authors [2, 5]. The purpose of this review is to analyze the medical literature pertaining to comparisons of MRI with MRA and CTA to DSA. In addition, this review sets out to determine whether, based on comparisons with DSA, the medical literature favors either CTA or MR techniques (i.e., MRI alone or in conjunction with MRA) for evaluation of the patient with suspected dissection of the craniocervical arteries. It is hoped that, from such a comparison, the reader can ascertain the relative merits of each imaging technique and assess the limitations of both. This review is not intended as a meta-analysis of the medical literature, which would include stratification of articles according to efficacy criteria, such as diagnostic-thinking efficacy and patient-outcome efficacy. Such a meta-analysis would appropriately include statistical analysis appropriate to assess the power of the studies used in the review. Materials and Methods We reviewed the medical literature on use of MRI, MRA, and CTA for articles reporting the use of these techniques for detection of dissection of the carotid and vertebral arteries. A MEDLINE search was using the search terms carotid, vertebral, craniocervical, artery, dissection, sensitivity, specificity, MRI, MR angiography, helical, MDCT, and CT angiography. This search was most recently on February 12, Only articles written in the English language were considered for review. This search revealed 66 articles that met the criteria, which were then reviewed. In addition, a wider search of published articles on the topic of carotid artery and vertebral artery dis- AJR:193, October

2 Provenzale and Sarikaya section was, in which another 25 articles on these topics were reviewed for indications of discussion of test performance characteristics for MRI, MRA, and CTA for detection of arterial injury. Articles that did not compare test performance of MRI, MRA, or MDCT against DSA as a reference standard were excluded, leaving a total of 21 articles (Table 1) for analysis. Test performance characteristics were recorded and compared across studies. For the 21 articles of interest, the imaging study, number of patients undergoing evaluation by MR techniques or CTA, percentage undergoing DSA, number of dissections, sensitivity, and specificity as well as (when available) the positive predictive value (PPV) and negative predictive value (NPV) were recorded (Table 1). To consider the effect of study design on test performance characteristics, we also noted whether a study was prospective or retrospective in nature (Table 1). Details of the imaging techniques used in each study were also recorded (Tables 2 and 3). In most articles, the PPV and NPV were not provided, but on occasion they could be calculated from data provided. Solely MRI TABLE 1: Sensitivity and Specificity of CT Angiography (CTA) or MR Angiography (MRA) for Detection of Cervicocephalic Arterial Dissection in Articles in Which These Techniques Were Compared With Digital Subtraction (Catheter) Angiography (DSA) Article Imaging Method a Study Design No. of Patients Undergoing MRI, MRA, or CTA Dissection Type (No.) Percentage of Patients Undergoing DSA No. of Dissections Affected Artery (No.) Sensitivity (%) Specificity (%) Müllges et al. [6], 1992 MRI P 5 S C (5) 100 Kitanaka et al. [7], 1994 MRI R 5 NS V (5) 100 Levy et al. [8], 1994 MRI, MRA P 180 NS C (19), V (5) 79 b 99 Zuber et al. [9], 1994 MRI R 15 NS C (9), V (10) 100 Leclerc et al. [15], 1996 CTA (1) I 16 NS C (18) Ozdoba et al. [10], 1996 MRI R 31 NS C (12) 80 Stringaris et al. [11] c, 1996 MRI, MRA I 12 NS C (12) Yoshimoto and Wakai [12], MRI, MRA R 11 S V (13) Mascalchi et al. [13], 1997 MRI, MRA R 14 S (10), T (4) V (12) 100 Auer et al. [14], 1998 MRI, MRA R 19 S (7), T (12) V (17) Múnera et al. [16], 2000 CTA (1) P 60 T C (7), V (3) Biffl et al. [25], 2002 MRI, MRA P 16 T NS CTA (1) P Miller et al. [26], 2002 CTA (4) P 143 T C (17), V (30) MRI, MRA P C (4), V (17) Chen et al. [17], 2004 CTA (4) R 17 S (15), T (2) V (19) Bub et al. [18] d, 2005 CTA (1, 4, 8) R 32 T C (12), V (5) Schneidereit et al. [19], 2006 CTA (8) P 170 T NS 65 Utter et al. [20] e, 2006 CTA (16) R 372 T 30 7 C (4), V (3) 92 Eastman et al. [21], 2006 CTA (16) P 162 T C (20), V (26) Malhotra et al. [22], 2007 CTA (16) P 119 T C (13), V (13) Pugliese et al. [23], 2007 CTA (4) R 15 S (12), T (3) V (15) Sliker et al. [24] f, 2008 CTA (16) R 108 T 100 NS NS WB CTA: 69, 74 g WB CTA: 82, 91 Neck: 64, 68 Neck: 94, 100 Note PPV = positive predictive value, NPV = negative predictive value, P = prospective, R = retrospective, I = indeterminate, S = spontaneous dissection, NS = not specified, T = traumatic dissection, C = carotid artery, V = vertebral artery, WB = whole-body, dash indicates not applicable. a Numbers in parentheses indicate single-detector or 4-, 8-, or 16-MDCT scanner. b 100% sensitivity for carotid dissection and 20% sensitivity for vertebral dissection. c MRI and MRA were compared with DSA but DSA did not serve as reference standard. DSA had a sensitivity of 91% and a specificity of 100%. d Values cited in this article represent combined test characteristics for three readers for both carotid artery dissection and vertebral artery dissection, although they are reported separately for individual readers and for type of artery in the article cited. e DSA was solely in patients with normal and equivocal CTA studies. Authors were primarily interested in negative predictive value; 271 patients with normal CTA were further evaluated, and 82 underwent DSA, which was positive in seven. Authors relied on reports for imaging findings, except retrospective review of false-negative case. f Authors compared two different CTA protocols with DSA and their analysis was based on (arbitrarily) designated vessel segments and thus total number of dissections. The distributions could not be deduced. Sensitivities and specificities are given for vessel segments for each protocol. Authors relied on DSA reports to extract results. g Values are for cervical carotid artery and vertebral artery, respectively. PPV (%) NPV (%) 1168 AJR:193, October 2009

3 MRI, MRA, and CTA in Diagnosis of Artery Dissection or MRI in combination with MRA was compared with DSA in nine articles [6 14], solely CTA was compared with DSA in 10 articles [15 24], and both CTA and MRA were compared with DSA in two articles (with CTA generally being in a different group of patients than the group undergoing MRA in the same study) [25, 26]. TABLE 2: Features of MR Scanners Used in Cited Articles Article Müllges et al. [6], 1992 Kitanaka et al. [7], 1994 Levy et al. [8], 1994 Zuber et al. [9], 1994 Ozdoba et al. [10], 1996 Imaging Technique MR Scanner Field Strength (T) Results The 21 articles that met the inclusion criteria were published over a 17-year interval. Three CTA studies were using single-detector scanners [15, 16, 25], and nine studies were using either solely MDCT scanners [17, 19 24, 26] or (in one case) predominantly MDCT scanners [18] (Tables 1 and 3). We did not include one article that reported four dissections but in which DSA was solely in two patients [27]. The number of patients undergoing either CTA or MR techniques in any one study varied between five and 372. The percentage of patients undergoing DSA in any one study varied between 14% and 100%, MRI Sequences MRA Contrast Material Administration MRI 1.5 T1W, T2W, PDW MRI 0.5 T1W, T2W MRI, MRA 1 Sagittal and axial SE T1W, axial SE T2W MRI 0.5 Axial T1W and T2W MRI 1.5 Sagittal T1W; axial T1W, PDW, T2W; axial and coronal fat-saturated T1W Unenhanced Technique of Unenhanced MRA FISP (additional 3D TOF for head in eight patients) with all patients undergoing DSA in 14 articles. As the table shows, in some articles, solely the sensitivity and specificity (and not the PPV and NPV) were provided. In one article, the reader could derive the PPV (but no other test performance characteristic) from data presented [19]. The articles listed in Table 1 vary considerably in the amount of information regarding age of dissections. In eight articles in which imaging was for assessment of neck injury, no specific information Technique (2D vs 3D) Slice or Slab Thickness (mm) Matrix Size and Field of View (FOV) Matrix, ; FOV, 25 cm 3D MRI: 7; MRA: 1 MRI: matrix, ; FOV, 230 mm; MRA: matrix, ; FOV, mm mm slice thickness with 1.5-mm gap and thin sections (3-mm slice thickness with 0.5-mm gap) for fat-saturated T1W sequences Yoshimoto and MRI, MRA Wakai [12], 1997 Mascalchi et al. [13], 1997 Auer et al. [14], 1998 Biffl et al. [25] a, 2002 Miller et al. [26] a, 2002 MRI, MRA 0.5 Sagittal T1W, axial PDW and T2W with additional sequences in majority of patients MRI, MRA 1.5 T1W, PDW, and T2W in at least 2 orthogonal planes Unenhanced PC and TOF PC: 2D (two patients), TOF: 2D (four patients) and 3D (one patient) Unenhanced MRA 1. 5 Not Unenhanced and contrastenhanced (3D FLAIR) TOF (FISP) for head and 3D FLASH (coronal) for neck TOF 3D (additional coronal 2D TOF in some patients) 2D and 3D TOF, 3D FLAIR MRI: 5 7; PC: (coronal or sagittal); 2D TOF: 3; 3D TOF: 1 MR: not specified; 3D TOF: 1; 2D TOF: not specified; FLASH: not specified MRI: not specified; PC: matrix, ; FOV, cm; 2D TOF: matrix, ; FOV, cm; 3D TOF: not specified MRA 0.2 Not Unenhanced TOF 2D Note MRA = MR angiography, TW1 = T1-weighted imaging, TW2 = T2-weighted imaging, PDW = proton density weighted imaging, SE = spin-echo, FISP = fast imaging with steady-state precession, TOF = time-of-flight MRA, PC = phase contrast MRA. a For studies that implemented both MR techniques and CTA, solely MR parameters are given here. AJR:193, October

4 TABLE 3: Features of CT Scanners Used in Articles Cited Provenzale and Sarikaya Article CT Equipment a (mm) Collimation Leclerc et al. [15], 1996 Múnera et al. [16], 2000 Biffl et al. [25] b, 2002 Miller et al. [26] b, 2002 Chen et al. [17], 2004 Bub et al. [18], 2005 Schneidereit et al. [19], 2006 Utter et al. [20], 2006 Eastman et al. [21], 2006 Malhotra et al. [22], 2007 Pugliese et al. [23], 2007 Sliker et al. [24], 2008 regarding age of dissection was provided [16, 18 22, 25, 26]. However, presumably imaging was within a few days of injury. Eight articles dealing with either spontaneous dissections or traumatic dissections reported findings on dissections that were thought to range between 3 days and 6 weeks old [7 9, 12, 13, 15, 17, 24]. Information regarding the age of dissections was not available in three articles [11, 14, 23]. This study assessed dissections in all segments of the carotid and vertebral arteries. Articles rarely stated locations of dissections along the length of the involved artery, so it is not possible to determine how many dissections were intracranial as opposed to extracranial. Nonetheless, based on images provided and the discussion within all articles, it appears that the overwhelming majority of dissections were in the extracranial segments. Slice Thickness and Reconstruction Increment (mm) Pitch Table Speed Position and Imaging Volume Voltage (kvp) Tube Current (mas) Helical mm/s Supine, head tilted back, C2 C6; total coverage: 90 mm Helical mm/s C7 to base of mandible Helical 1,1 interval 2 C3 to sella turcica MDCT (4) 1 1 2:1 Aortic arch to skull base MDCT (4) mm per rotation, 9.4 mm/s Helical and MDCT (4, 8) 2.5 (MDCT protocol) 1 3 (varied depending on the CT equipment) 1.35:1 (MDCT protocol) MDCT (8) 1.25, 0.9 interval 1.35: mm/s/per rotation Aortic arch to circle of Aortic arch to circle of Aortic arch to circle of MDCT (16) 2. 5 Aortic arch to circle of MDCT (16) 1.25, 0.5 interval Aortic arch to vertex MDCT (16) Aortic arch to circle of MDCT (4) mm/per rotation MDCT (16) Whole-body, 1.0; neck, 0.9 a Numbers in parentheses indicate single-detector or 4-, 8-, or 16-MDCT scanner. b For studies that implemented both MR techniques and CTA, only CTA parameters are given here Whole-body: arms abducted, circle of to lung bases or ischial tuberosities; neck: arms adducted, aortic arch to circle of MR Techniques for Evaluation of Carotid Artery and Vertebral Artery Dissection For purposes of this review, all articles that, in any manner, compared MR techniques with DSA are discussed together. Thus, articles that solely compared MR techniques with DSA [6 14] will be discussed along with the MRI portions of articles that compared both CTA and MR techniques against DSA [25, 26]. In these 11 studies, a total of 329 patients were evaluated (with approximately 55% enrolled in one study [8]) and 144 dissections were reported. The reported sensitivity of MR techniques for detection of arterial dissection ranged from 50% to 100%. As Table 1 indicates, the specificity rate also varied considerably across studies, from 29% to 100%. In the two studies that compared both CTA and MR techniques with DSA, the sensitivity and specificity for CTA and MR techniques were similar to one another (Table 1). One study reported sensitivity for CTA and MR techniques of approximately 50% and a specificity of approximately 98% [26]. In another study, both CTA and MR techniques had a sensitivity and specificity of approximately 70%; the PPVs for CTA and MR techniques were 65% and 43%, respectively, and the NPVs for CTA and MR techniques were 70% and 89%, respectively [25]. The largest series using MRI and MRA, which reported 24 dissections on DSA in 180 patients, showed good sensitivity and specificity rates of 83% and 99%, respectively [8]. Notably, in that study, sensitivity and specificity of MRI with MRA differed substantially for carotid artery dissection compared with vertebral artery dissection. For carotid dissections, MRI and MRA had a sensitivity of 95% 1170 AJR:193, October 2009

5 MRI, MRA, and CTA in Diagnosis of Artery Dissection and a specificity of 99%. For vertebral artery dissection, MRI and MRA had a sensitivity of 20% and a specificity of 100%. In one small study of 12 patients with dissection, MRI and MRA were compared with DSA; however, in that study, DSA was not considered as a reference standard [11]. Instead, in cases in which the DSA study was interpreted as negative and the combination of MRI and MRA was considered positive, the MR studies were considered correct. DSA was determined to have a sensitivity of 91% and a specificity of 100%. Importantly, the PPV, which is the proportion of patients with dissections who were correctly diagnosed, was reported in only one article, in which it was found to be only 43% [25]. In that same study, NPV was reported to be 89% [25]. The remaining articles did not provide data that allowed these important values to be calculated. Sensitivity values for retrospective studies using MR techniques, which ranged from 95% to 100%, were higher than for prospective studies, which ranged from 50% to 79%. Specificity values for prospective studies ranged from 67% to 99%; the only specificity value available for a retrospective study was 29%. Because a PPV and an NPV were available for only one article involving MR techniques, comparison between retrospective studies and prospective studies was not possible for those indices. CTA for Evaluation of Carotid Artery and Vertebral Artery Dissection The number of studies for which CTA has been compared with DSA was found to be much larger than those using MRI and MRA, with substantially more patients reported in the CTA studies. A total of 1,277 patients underwent CTA in the combined studies, and 242 arterial dissections were found on DSA. In one article, the number of dissections could not be deduced [24]. The sensitivity values ranged between 51% and 100%, and the specificity rates varied between 67% and 100%. Notably, three of the 10 studies that reported sensitivity found a sensitivity rate of 100% [15, 17, 23] and five of the 10 studies that reported specificity indicated a specificity rate of at least 95% [16, 17, 21, 23, 26]. A PPV was reported in eight studies and ranged from 65% to 100% [16 19, 21 23, 25]. An NPV was reported in eight series and varied between 70% and 100% [16 18, 20 23, 25]. Among the CTA articles we reviewed, 25% were using single-detector CT scanners [15, 16, 25]. Comparing results obtained using MDCT scanners and those obtained using single-detector scanners, one finds that a moderate improvement in some (but not all) of the test characteristics has been reported with MDCT scanners. Sensitivities for retrospective CTA studies ranged from 64% to 100%, and those for prospective studies ranged from 51% to 98%. Specificities for retrospective CTA studies ranged from 82% to 95%, and those for prospective studies ranged from 67% to 100%. PPVs for retrospective CTA studies ranged from 68% to 94%, and those for prospective studies ranged from 65% to 100%. NPVs for retrospective CTA studies ranged from 92% to 100%, and those for prospective studies ranged from 70% to 98%. Thus, the range of values for any single test performance characteristic was similar for retrospective CTA studies and for prospective CTA studies. Discussion This review showed that the reported sensitivity and specificity of MR techniques and CTA for diagnosis of craniocervical arterial dissection are relatively similar. In this review, with one exception, only articles that compared MR techniques or CTA with DSA as a reference standard were considered. As some authors have pointed out, DSA is an imperfect reference standard because of interobserver variability and a number of entities that can mimic arterial dissection [23]. Nonetheless, the choice of solely articles in which DSA served as a comparison study for this review can be justified because, at least for the present, DSA is widely considered by the radiologic community as the reference standard for cross-sectional angiographic imaging studies. In the future, it is possible that a noninvasive imaging technique may serve as a reference standard, building on the previous small study suggesting that MR techniques are superior to DSA [11]. However, for that to be the case, a large study comparing techniques will be needed. This review also showed that the reported PPVs and NPVs for CTA are very good. Unfortunately, because PPV and NPV have rarely been reported for studies using MR techniques, a comparison with CTA with regard to those values cannot reasonably be. One limitation we found in attempting to compare studies using MRI techniques is that the age of the dissections in patients was often poorly outlined. This fact confounds an attempt to determine reasons for differing test performance characteristics between imaging tests for dissection. The age of the dissection is an important consideration because the degree of bright signal on T1- and T2-weighted MR images, and thus one factor determining the conspicuity of dissections on MRI, is dependent on the age of the dissection. However, the age of dissection is difficult to determine in cases of spontaneous dissection. Often, one can only assume that the time of onset of dissection corresponds to the time of onset of symptoms and signs; however, this assumption may not be true in all cases. MRI and MRA for Evaluation of Carotid and Vertebral Artery Dissection The test performance characteristics reported in the studies using MR techniques varied substantially. Many possible explanations could account for this fact. Study design, experience of readers interpreting scans or DSA studies, available MR technology, postprocessing, and workstation capability are a few of the reasons that are likely important. One factor to be considered in evaluating variation between studies is whether solely a clearly abnormal study is considered a positive imaging study or whether equivocal studies, which in clinical practice would lead to further imaging, should also be considered. For instance, one investigator, noting that recognition and evaluation of equivocal findings is important for maximizing sensitivity, argues that equivocal findings should be considered as positive studies [18]. Such a practice would also conform to clinical practice in that equivocal studies are typically followed by a more definitive test. Because MRI and MRA were developed earlier than CTA techniques, comparisons of DSA against MRI and MRA were conducted earlier than CTA comparisons. No article indicating test performance characteristics for MRI and MRA published after 2002 was found, compared with eight CTA studies that provided information after Thus, newer techniques such as bolus-timing and timeresolved contrast-enhanced MRA are not included. Unfortunately, the test characteristics of MRA using more recent techniques have not been determined. Thus, information on trends in test performance of MRI and MRA over the past few years, after development of the aforementioned technologic advances, is lacking, whereas (as discussed later) such trends can be followed for CTA. CTA for Evaluation of Carotid and Vertebral Artery Dissection This review found that sensitivity of CTA in some studies in which it was compared AJR:193, October

6 Provenzale and Sarikaya with DSA is lower than in some CTA studies in which tests other than DSA (e.g., clinical examination or surgical findings) served as the sole reference standard (outlined later). A possible explanation for this discrepancy in sensitivity values is that DSA is more sensitive than these other tests for subtle dissections. Examples of studies in which the sensitivity and specificity of CTA were determined primarily on the basis of clinical follow-up include the following articles: In one study of 106 patients assessed with a 4-MDCT scanner in whom the final diagnosis was determined by various forms of imaging, surgical procedures, or clinical follow-up, the reported sensitivity for detection of vascular and aerodigestive tract injuries was 100% and specificity was 94% [28]. In another prospective study of 175 patients, the reference standard for positive CTA studies was catheter angiography or surgery, and for negative studies clinical follow-up served as the reference standard [16]. The reported sensitivity was 100% and specificity was 99%. Finally, in another study examining the use of CTA for detection of arterial injury in patients with blunt cervical trauma, MRA was the primary reference standard; among the 11 arterial injuries noted among 407 patients, sensitivity was recorded as 100% and specificity as 99% [2]. As with studies using MR techniques, marked variation was seen in test performance characteristics for CTA studies. Again, a number of possible explanations exist for these differences between studies, which have been outlined in the earlier discussion of variations in MRI and MRA test performance. As an example of the possible role of reader experience, in one study, all false-negative CTA examinations were recorded in the first half of the study, indicating the likelihood that test performance, in some cases, is substantially dependent on the level of experience of the individual interpreting the study [22]. Other potential reasons for variability in test performance characteristics, specifically for CTA studies, are advances in technology. In the past decade, considerable advances have been made in the design of helical CT scanners, e.g., development of MDCT capability on the order of 16 or more slices, improvements in contrast bolus timing mechanisms, and developments in image processing programs and workstations. For instance, CTA data can be viewed as source images, maximum-intensity-projection images, volume-rendered (3D reconstruction) images, and multiplanar reformation images. Furthermore, much greater (and wider) experience has been gained in the last decade by radiologists in assessment of CTA imaging studies. Thus, it is natural to ask whether the performance characteristics for CTA have improved over time. For instance, in one study, investigators compared results of screening patients with blunt cervical trauma obtained using 16-MDCT helical CTA with those previously obtained using 4-MDCT helical CTA and found an approximately threefold increase in incidence of carotid or vertebral artery dissection using 16-MDCT CTA [29]. However, these differences, although suggestive of the importance of technologic advances in providing greater accuracy, could be explained by a number of other factors, e.g., differences in patient populations screened by 4-MDCT and 16-MDCT techniques or increased familiarity of radiologists with CTA images. Nonetheless, the comparison of test performance characteristics for single-detector CTA and MDCTA studies outlined in Tables 1 and 3 shows, in general, better test performance characteristics for MDCT scanners than for single-detector scanners. The specificity and NPV were generally higher for MDCT studies. These improved test characteristics are concordant with the reported improved test characteristics of high-resolution MDCTA for other purposes, e.g., for detection of carotid stenosis [30]. Although this review showed that the test characteristics of studies using MR techniques and CTA were relatively similar, some investigators have indicated a preference for CTA for diagnosis of dissection. For instance, some authors have pointed out that limitations found using MRI and MRA (e.g., obscuration of mural hematoma by the hyperintense signal of thrombus within an occluded artery and lack of hyperintense signal within mural hematoma on T1-weighted images in the first few days after onset of dissection) are overcome by CTA [31]. Another study (which did not compare CTA or MRA against DSA and hence is not included in our tables) found that CTA frequently depicted more findings indicative of dissection (e.g., more frequently found intimal flaps and pseudoaneurysms) than MRI and MRA [32]. It may be asked under what circumstances DSA should be for dissection, when noninvasive tests without patient risk are available. The first circumstance involves cases in which CTA, MR techniques, or both provide discrepant results. For instance, on MR studies, when some pulse sequences suggest the presence of dissection and other sequences indicate absence of dissection, it may not be clear which sequences should be taken as representing truth. Depending on the level of comfort with CTA of the radiologist interpreting the imaging findings, DSA may be the most appropriate next study. Similarly, when discrepant or equivocal results are seen on CTA, the radiologist s experience with MR techniques may favor DSA as the most suitable next study. The second circumstance involves acute clinical situations in which, if a dissection is found, an endovascular procedure (e.g., intraarterial stent placement) will likely be needed soon afterward. In such cases, in the interest of time, DSA could reasonably be deemed the most appropriate diagnostic study. Finally, it is, of course, indicated that, if DSA is already being on vessels other than the carotid or vertebral arteries and dissection of the craniocervical arteries is suspected, then those arteries are also included as part of the DSA procedure. Limitations This review was limited in its conclusions by the heterogeneous nature of the medical literature on the use of MR techniques and CTA in assessment of arterial dissection. We recognize the many limitations inherent in a review in which many different types of studies were pooled. Studies substantially differed from one another in degree of detail regarding such features as patient characteristics, ages of dissections, and cause of dissections. Furthermore, a great degree of variability in study design, methods of selection of patients, scanner capability, and imaging parameters and techniques was seen. For these reasons, conclusions regarding a comparison of MR techniques and CTA for diagnosis of arterial dissection of the craniocervical arteries must be viewed with caution. In many instances, study features that could strongly influence test performance characteristics (e.g., potential sources of bias in studies) are not evident to the reader, making comparison of studies difficult. It is worth noting that many of the articles discussed in this review pertain to traumatic dissection rather than spontaneous dissection. This fact is particularly true for articles written from the perspective of trauma surgeons or emergency department physicians seeking to understand the use of imaging as a screening tool for traumatic carotid or verte AJR:193, October 2009

7 MRI, MRA, and CTA in Diagnosis of Artery Dissection bral artery dissection. Thus, it is possible that the cumulative findings discussed here may not adequately reflect rates of detection for spontaneous dissections. Summary In conclusion, this review of the medical literature showed that, in general, the test characteristics of MRI combined with MRA were quite similar to those of CTA for diagnosis of dissection of the carotid and vertebral arteries. Clearly, both imaging techniques have unique advantages as well as pitfalls that serve to diminish sensitivity and specificity. However, the evidence obtained from this review does not indicate superiority of one technique as applied to a population of patients with carotid or vertebral artery dissection. Optimally, a formal prospective study with blinded readers and a well-defined patient population that might better compare imaging techniques would answer the questions we raised. However, it is unlikely that such a study will be in the future. Therefore, it is reasonable that individual users exercise their own preference based on specific clinical situations (e.g., ease of obtaining the imaging study, ability to couple the imaging study with other imaging tests so as to conserve time in managing patients) and degree of comfort with one particular technique. At our institution, CTA is routinely chosen for imaging the trauma patient because it allows multiple sites of injury (including those outside the head and neck) to be evaluated on a single scanner in close temporal order. However, that choice is based on consensus among the neuroradiologists at our institution rather than on evidence culled from the medical literature indicating a clear superiority of CTA for diagnosis of dissection. At our institution, patients with suspected arterial dissection that is not related to trauma are evaluated by either MRI combined with MR angiography or CTA in relatively equal numbers. On the basis of our review, it appears that individual readers, in conjunction with physicians ordering studies, may choose the study technique based on individual factors such as urgency of patient s clinical condition in relation to scanner availability, coexisting diagnoses under consideration, and degree of radiologist experience with imaging techniques in this setting. References 1. Schievink WI. Spontaneous dissection of the carotid and vertebral arteries. N Engl J Med 2001; 344: Mutze S, Rademacher G, Matthes G, Hosten N, Stengel D. Blunt cerebrovascular injury in patients with blunt multiple trauma: diagnostic accuracy of duplex Doppler US and early CT angiography. Radiology 2005; 237: Rogers FB, Baker EF, Osler TM, Shackford SR, Wald SL, Vieco P. 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