Intimal Tears in Thoracic Aortic Dissection: Appearance on MDCT With Virtual Angioscopy

Transcription

1 Vascular and Interventional Radiology Pictorial Essay Maldjian and Partyka MT of Intimal Tears in Thoracic ortic issection Vascular and Interventional Radiology Pictorial Essay ownloaded from by on 01/07/18 from IP address opyright RRS. For personal use only; all rights reserved Pierre. Maldjian 1 Luke Partyka Maldjian P, Partyka L Keywords: aortic dissection, intimal tears, virtual angioscopy OI: /JR Received June 5, 2011; accepted after revision ugust 14, oth authors: epartment of Radiology, University Hospital, UMNJ-NJ Medical School, 150 ergen St, UH -320, Newark, NJ ddress correspondence to P.. Maldjian (maldjipd@umdnj.edu). ME This article is available for ME credit. JR 2012; 198: X/12/ merican Roentgen Ray Society Intimal Tears in Thoracic ortic issection: ppearance on MT With Virtual ngioscopy OJETIVE. The location, number, size, and configuration of intimal tears in aortic dissection have important therapeutic and prognostic implications. Planning of procedures to treat complications of aortic dissection may require precise delineation of the intimal tears. The purpose of this article is to illustrate the ability of MT using multiplanar image reformatting and virtual angioscopy to depict the location and appearance of intimal tears and fenestrations within dissection flaps in cases of thoracic aortic dissection. ONLUSION. MT with virtual angioscopy can depict the configuration of intimal tears in cases of thoracic aortic dissection, which may facilitate therapeutic planning. issection is the most common acute emergent disorder of the thoracic aorta and requires early diagnosis and treatment to improve prognosis. Thoracic aortic dissections are classified by location according to the Stanford scheme as type if the ascending aorta is involved and as type if the dissection begins distal to the origin of the left subclavian artery. Type dissections are usually managed surgically to prevent life-threatening complications resulting from proximal extension of the dissection, such as cardiac tamponade resulting from hemopericardium, myocardial infarction resulting from coronary artery involvement, or acute severe valvular insufficiency resulting from disruption of the aortic valve. Type dissections are usually managed medically with blood pressure control to prevent progression of the dissection, unless there are associated complications, such as rupture, leak, branch vessel ischemia, or aneurysm. issections can also be classified according to the duration. issections of less than 14 days since the onset of symptoms are considered acute, whereas those beyond this interval are considered chronic. hronic type dissections are managed with antihypertensive medication and close surveillance. Progressive aneurysmal dilation of the aorta is the most common indication for intervention in chronic dissection [1]. The dissection flap, which is composed of intima and a thin layer of media, contains one or multiple sites of intimal injury, allow- ing communication between the true and false lumens. The size, configuration, and locations of these intimal tears have important implications in treatment planning. Large intimal tears in the proximal aorta appear to increase the tendency of true lumen collapse, contributing to branch vessel ischemia [2]. For surgical therapy of type thoracic aorta dissection, the site of the intimal tear must be repaired to eliminate the entry of blood into the false lumen. This reverses the collapse of the true lumen, alleviates dynamic obstruction of aortic branches, and helps to stabilize the remainder of the dissection [3]. The location of the intimal tear affects the extent of the surgical procedure. If the intimal tear resides in the aortic arch, this will require resection of the portion of the arch containing the tear (usually along the lesser curvature) and reconstruction of the remainder of the arch (a hemiarch procedure) [4]. There is also experimental evidence suggesting that the sizes and locations of intimal tears affect the pressures in the false lumen, altering the rate of false lumen expansion [5]. primary goal of treatment of dissections with endograft placement is to occlude the primary intimal tear to improve true lumen flow and induce false lumen thrombosis. ssessing fenestrations in the dissection is also important because these contribute to maintaining patency of the false lumen [1]. overing these small distal fenestrations with stentgrafts has produced favorable results [6]. Furthermore, if percutaneous fenestration of JR:198, pril

2 Maldjian and Partyka ownloaded from by on 01/07/18 from IP address opyright RRS. For personal use only; all rights reserved the dissection flap is needed for treatment of malperfusion syndrome as a complication of aortic dissection, preoperative planning requires accurate delineation of existing tears in the dissection flap [7]. MT angiography has emerged as a robust noninvasive modality for the evaluation of aortic dissections. With thin-section imaging and acquisition of isotropic datasets, high-quality images can be reconstructed in any chosen plane. In addition to multiplanar image reformatting and volume rendering, virtual angioscopy can also be used to facilitate evaluation of aortic disorders. Virtual angioscopy is an image-processing technique that uses datasets from T angiography to render endoluminal views of blood vessels. Using a computer workstation, the interpreter can interactively evaluate the inner walls of blood vessels. ecause it produces a 3 representation of the aortic surface topography, virtual angioscopy provides a more intuitive understanding of the size, configuration, and location of intimal tears. From the endoluminal perspective, one can also easily navigate the curvature of the aorta to determine the relationship of intimal abnormalities to ostia of branch vessels. recent study in patients treated for thoracic aortic dissection reports that virtual T angiography can provide additional information complementary to multiplanar reformatted views, including precise localization of residual intimal tears [8]. The purpose of this article is to illustrate the ability of MT with virtual angioscopy to display intimal tears associated with aortic dissections because this can play a role in planning therapeutic procedures [9, 10]. MT Technique Representative images from T performed on patients with dissections of the aorta were selected for this presentation. ll T examinations were performed on a 16-MT scanner (LightSpeed 16, GE Healthcare) using the following parameters: kvp, automatic current tube modulation with maximum tube current of 550 m and noise index of 17, 0.6-second rotation, mm collimation, and pitch of 1.375:1. Images were reconstructed at 1.25-mm thickness at 1.25-mm intervals. Scanning was performed from the top of the chest to the level of the aortic bifurcation in the abdomen. n IV bolus of about 150 ml of iodixanol (320 mg I/ ml; Visipaque, GE Healthcare) was given at a flow rate of 4 5 ml/s. Scanning was performed in the arterial phase, with the scan delay determined using bolus-tracking software (SmartPrep, GE Healthcare). Postprocessing was performed on a free-standing workstation (dvantage 4.2, GE Healthcare). Virtual angiography images were generated with a dedicated software tool (Navigator, GE Healthcare). Regarding virtual angioscopy, to enable clear visualization of the vessel walls, the blood pool within the vessel is rendered translucent by adjusting a threshold that excludes high-attenuation voxels ( HU) from the reconstructed virtual angioscopy images. ecause the attenuation of the vessel walls is well below these values, the walls are usually well defined. For the cases presented here, the threshold was adjusted to allow maximum translucency of the vessel lumen while maintaining a smooth appearance of the vessel wall. Virtual angioscopy can produce artifacts if the attenuation of the blood pool is not uniformly high or if the attenuation of the vessel wall is not uniformly low. Speckles or floating-shape artifacts occur in the vessel lumen when low-attenuation voxels within the lumen are misinterpreted by the software as separate from the blood pool and rendered as separate intraluminal objects. Spurious holes in the vessel wall or in the dissection flap are produced when the attenuation of a portion of the vessel wall or flap is not low enough to be recognized as a boundary by the software, resulting in a discontinuity along the surface [11]. To avoid confounding artifacts, the presence and location of an intimal tear must first be confirmed on multiplanar 2 images before depiction of the tear with virtual angioscopy. lso, because virtual angioscopy is a depiction of a 3 view, it is not accurate for measurement of fenestration diameters. ny measurements should be performed on reformatted multiplanar 2 views. Thus, virtual angioscopy images must always be interpreted in conjunction with the axial source images and reformatted multiplanar 2 views. Illustrative ases MT with virtual angioscopy can reveal the site and configuration of entry tears in acute aortic dissection (Figs. 1 and 2). ecause of motion of the ascending aorta resulting from cardiac pulsation, acute dissections of the ascending aorta near the root are best evaluated with MT using EG-gating (Fig. 3). issection flaps often have multiple fenestrations, which occur commonly at branch points along the vessel, especially near the renal arteries. ny branch vessel supplied by the false lumen is usually accompanied by a small fenestration in the dissection flap because the flap must shear the branch vessel at the origin [12]. Fenestrations contribute to persistent patency and pressurization of the false lumen, increasing the risk of expansion and rupture [1]. MT with virtual angioscopy can facilitate evaluation of the dissection flap for fenestrations (Figs. 4 and 5). With chronic dissections, persistent entry tears or fenestrations in the dissection flap can maintain patency of the false lumen, leading to progressive enlargement of the false lumen (Figs. 6 and 7). fter surgery for repair of the ascending aorta in patients with dissections involving the ascending and descending aorta, the false lumen and dissection flap in the descending aorta remain intact. MT with virtual angioscopy can be used to evaluate fenestrations and collateral vessels that maintain patency of the false lumen in such patients after surgery (Fig. 8). MT can also depict features helping to differentiate the true lumen from the false lumen. The false lumen is usually larger than the true lumen and commonly deforms the shape of the true lumen (Figs. 4 and 6). Flow in the false lumen is usually slower than that in the true lumen; hence, the attenuation of the false lumen tends to be lower and more heterogeneous than the attenuation of the true lumen because of mixing of contrast agent with unopacified blood. Thrombus formation after dissection is more likely in the false lumen than in the true lumen. obwebs (i.e., tissue strands connecting the dissection flap to the vessel wall) also help to definitively identify the false lumen [13] (Fig. 8). For treatment of a type aortic dissection, a covered stent can be placed over the intimal tear through which blood otherwise flows to the false lumen. The stent thus covers the entry site and maintains patency of the true lumen, facilitating thrombosis of the false lumen. irecting flow into the true lumen promotes favorable remodeling of the aorta [3]. MT and virtual angioscopy can be helpful for evaluating the results and complications of endovascular repair (Fig. 9). onclusion MT with virtual angioscopy of aortic dissections can facilitate visualization of entry tears and fenestrations in dissection flaps. This information may be useful as an adjunct in preoperative planning and for assessing the postoperative status of patients with aortic dissections. 956 JR:198, pril 2012

3 MT of Intimal Tears in Thoracic ortic issection ownloaded from by on 01/07/18 from IP address opyright RRS. For personal use only; all rights reserved References 1. Wong R, Lemaire S, oseli JS. Managing dissections of the thoracic aorta. m Surg 2008; 74: hung JW, Elkins, Sakai T, et al. True-lumen collapse in aortic dissection. Part I. Evaluation of causative factors in phantoms with pulsatile flow. Radiology 2000; 214: Golledge J, Eagle K. cute aortic dissection. Lancet 2008; 372: Moon MR. pproach to the treatment of aortic dissection. Surg lin North m 2009; 89: Tsai TT, Schlicht MS, Khanafer K, et al. Tear size and location impacts false lumen pressure in an ex vivo model of chronic type aortic dissection. J Vasc Surg 2008; 47: Yuan LX, ao JM, Zhao ZQ, et al. Simultaneous multi-tear exclusion: an optimal strategy for type thoracic aortic dissection initially proved by a single center s 8 years experience. hin Med J (Engl) 2007; 120: Willoteaux S, Lions, Gaxotte V, eregi JP. Imaging of aortic dissection by helical computed tomography (T). Eur Radiol 2004; 14: Louis N, ruguiere E, Kobeiter H, et al. Virtual angioscopy and 3 navigation: a new technique for analysis of the aortic arch after vascular surgery. Eur J Vasc Endovasc Surg 2010; 40: Verhoye JP, Sze Y, Ihnken K, Hellinger J, Robbins RR, ake M. Virtual angioscopy in type- dissection: ascending aortic stent-graft repair. nn Thorac Surg 2006; 82: Hornero F, ervera V, Estornell J, et al. Virtual vascular endoscopy for acute aortic dissection. nn Thorac Surg 2005; 80: Glockner JF. Navigating the aorta: MR virtual vascular endoscopy. RadioGraphics 2003; 23:e Quint LE, Platt JF, Sonnad SS, eeb GM, Williams M. ortic intimal tears: detection with spiral computed tomography. J Endovasc Ther 2003; 10: LePage M, Quint LE, Sonnad SS, eeb GM, Williams M. ortic dissection: T features that distinguish true lumen from false lumen. JR 2001; 177: Fig year-old woman with acute type dissection of descending thoracic aorta., xial image shows large intimal tear (arrow) opening into false lumen (FL)., Reformatted coronal maximum-intensity-projection image shows dissection flap extending to level of right renal artery (arrow). Right renal artery originates from FL., Virtual angioscopy image looking down into ascending aorta (o) and descending aorta from viewpoint of arrow in shows large intimal tear (arrows) opening into FL of descending thoracic aorta. In case such as this, if closure of this tear is contemplated (such as for placement of endovascular stent), it must be considered that perfusion to right kidney is dependent on flow in FL. = anterior, L = left, P = posterior, R = right, TL = true lumen. Fig year-old woman with acute type dissection of thoracic aorta., T image through arch shows tear (arrow) in dissection flap between true lumen (TL) and false lumen (FL). This represents entry tear because no other tear was found at subsequent surgery., Virtual angiography image looking up from TL just below arch shows intimal tear in dissection flap (arrows) opening into FL. 1 = ostium of right brachiocephalic artery, 2 = ostium of left common carotid artery, 3 = ostium of left subclavian artery, = anterior, L = left, P = posterior, R = right. JR:198, pril

4 Maldjian and Partyka ownloaded from by on 01/07/18 from IP address opyright RRS. For personal use only; all rights reserved Fig year-old man with acute aortic dissection., oronal reformatted view from EG-gated T scan shows dissection flap in ascending aorta (black arrows) separating true lumen (TL) from false lumen (FL). Note large entry tear (white arrow). Step-offs in flap (arrowheads) represent misregistration artifacts due to motion., Virtual angioscopy from perspective of white arrow in shows large intimal tear (arrows) opening into FL. pparent slits (arrowheads) represent misregistration artifacts. = anterior, I = inferior, P = posterior, S = superior. Fig year-old woman with type dissection of descending aorta., Volume-rendered image shows dissection flap (arrowhead) in descending aorta with large intimal tear (arrow), likely representing entry tear, opening into false lumen (FL). Note compression of true lumen (TL) by FL., Virtual angioscopy image from perspective of arrow in looking caudal shows large intimal tear (arrows) opening into FL. Note distortion of shape of TL due to compression from FL. = anterior, L = left, P = posterior, R = right., Reformatted oblique sagittal image shows small fenestration (arrow) in dissection flap at level of diaphragm. Note that FL compresses TL., Virtual angioscopy image looking down aorta from perspective of arrow in () shows small fenestration (arrow). gain note distortion of shape of TL due to compression from FL. = anterior, L = left, P = posterior, R = right. 958 JR:198, pril 2012

5 MT of Intimal Tears in Thoracic ortic issection ownloaded from by on 01/07/18 from IP address opyright RRS. For personal use only; all rights reserved Fig year-old woman with acute type dissection of descending aorta., Reformatted coronal image shows two small openings (white and black arrows) in dissection flap. Note that left renal artery (arrowhead) originates from false lumen (FL)., Virtual angiography image from inside true lumen (viewpoint of arrows in ) shows fenestrations (white and black arrows) in dissection flap opening into FL. Note ostium of left renal artery (arrowhead) that can be seen in FL. = anterior, I = inferior, P = posterior, S = superior. Fig year-old woman with chronic type dissection of descending aorta managed medically. Images are from follow-up T performed 2 years after initial presentation., Volume-rendered view shows aneurysm and dissection (arrow) of descending aorta. False lumen (FL) had been gradually increasing in size compared with prior studies. sterisk indicates true lumen (TL)., xial view shows intimal tear (arrow) in dissection flap, likely representing entry tear. Note marked compression of TL (asterisk) by aneurysmal FL., Virtual angioscopy looking down descending thoracic aorta shows intimal tear (arrows) opening into FL. Note marked narrowing of TL due to compression from FL. Persistence of large entry tear in this case maintains flow and pressurization of FL, resulting in compression of TL and progressive enlargement of FL. = anterior, L = left, P = posterior, R = right. Fig year-old woman with dissection of descending thoracic aorta., Oblique reformatted view from follow-up T study 7 months after presentation shows distal margin of dissection flap (black arrow) and channel of flow (white arrow) in distal false lumen (FL). istal FL had increased in size compared with initial study., xial view shows distal FL and fenestration (arrow) in dissection flap. oth fenestration and FL had increased in size compared with prior studies. (Fig. 7 continues on next page) JR:198, pril

6 Maldjian and Partyka ownloaded from by on 01/07/18 from IP address opyright RRS. For personal use only; all rights reserved E Fig. 7 (continued) 51-year-old woman with dissection of descending thoracic aorta., Virtual angiography image from perspective of arrow in shows large fenestration (arrows) in dissection flap. I = inferior, L = left, R = right, S = superior, TL = true lumen., Virtual angiography image looking up from below into FL from perspective of arrows in shows margins of large opening in dissection flap (white arrows) and patent channel (black arrow) in FL. = anterior, P = posterior, R = right, L = left. Fig year-old man with dissection of ascending and descending aorta who underwent repair of ascending aorta. Images are from follow-up T scan performed 2 years after surgery., T image at level of kidneys shows cobweb (arrow) in false lumen (FL, asterisk). obweb is ribbon of media sheared off by dissection that helps to definitively identify FL [13]. TL = true lumen., Virtual angioscopy image looking down FL shows cobweb (arrow). = anterior, L = left, P = posterior, R = right., xial maximum-intensity-projection image shows two small fenestrations (arrows) in dissection flap allowing communication between TL and FL (asterisk)., Virtual angioscopy close-up view of two small fenestrations (arrows) seen in. I = inferior, S = superior. E, Volume-rendered view of proximal abdominal aorta from left lateral perspective shows opacification of FL (asterisk). Most proximal part of opacified FL (black arrow) communicates with intercostal arteries (white arrows). ommunication with branch vessels can help maintain patency of FL. Note celiac artery (red arrow) originating from TL. F, Virtual angioscopy image looking up into proximal opacified FL (from perspective of black arrow in E shows ostia of intercostal arteries (arrows). F 960 JR:198, pril 2012

7 MT of Intimal Tears in Thoracic ortic issection ownloaded from by on 01/07/18 from IP address opyright RRS. For personal use only; all rights reserved FOR YOUR INFORMTION Fig year-old man with dissection of descending thoracic aorta., Reformatted oblique sagittal image in plane of aortic arch at initial presentation shows acute aortic dissection with intimal tear (arrow) likely representing entry tear. FL = false lumen., Virtual angioscopy from perspective of black arrow in inside true lumen (TL) looking up at dissection flap shows intimal tear opening into FL. I = inferior, L = left, R = right, S = superior., For treatment of dissection, patient had placement of endograft (black arrow) and placement of graft (white arrow) to innominate and left common carotid arteries because stent covers normal location of ostia of these vessels. FL remains patent because of type 2 endoleak from backflow in left subclavian artery (arrowhead)., Virtual angiography image from perspective of black arrow in shows struts of endograft (colored pink) and ostium of left subclavian artery (arrow) responsible for endoleak depicted in (). = anterior, P = posterior. This article is available for ME credit. Log onto click on JR (in the blue Publications box); click on the article name; add the article to the cart; proceed through the checkout process. JR:198, pril