CT angiography and MR imaging aspects of abdominal aortic aneurysms

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1 CT angiography and MR imaging aspects of abdominal aortic aneurysms Poster No.: C-1352 Congress: ECR 2013 Type: Educational Exhibit Authors: C. I. paltanea, R. A. Capsa, G. Popa, I. G. Lupescu ; Bucharest, sector :2/RO, Bucuresti/RO, Bucharest/RO Keywords: Arteries / Aorta, Abdomen, Vascular, CT-Angiography, MRAngiography, Diagnostic procedure, Computer ApplicationsDetection, diagnosis, Contrast agent-intravenous, Aneurysms DOI: /ecr2013/C-1352 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 27

2 Learning objectives To discuss the CT and MRI techniques used in the evaluation of abdominal aortic aneurysms (AAA). To review the contribution of Multidetector CT Angiography (MDCTA) and MR angiography (MRA), in the diagnosis of abdominal aortic aneurysm and its complications. To compare the indications and limits for both methods. To present and illustrate the current and particular aspects of AAA and their differential diagnosis. Background Definition. Aneurysms are defined as focal dilatations of an artery, with at least a 50% increase over its normal diameter. Therefore, an enlargement of at least 3 cm of the abdominal aorta fits the definition (1). Abdominal aortic aneurysms (AAAs) are relatively common and are potentially life threatening and usually result from degeneration in the media of the arterial wall, leading to a slow and continuous dilatation of the lumen of the vessel (1). Incidence varies strongly between males and females, (M/F 4-8/1). The peak of incidence is among males around 70 years of age, the prevalence at males over 60 years totals 2-6%. The frequency is much higher in smokers than in non-smokers (8:1), and the risk decreases slowly after the cessation of smoking (2). Other risk factors include hypertension and male sex (3). Imaging methods. Plain abdominal radiographs are used to show the outline of an aneurysm when its walls are calcified. Ultrasonography may be used to detect aneurysms and to determine its size. Additionally, free peritoneal fluid can be detected at US. It is a noninvasive and sensitive method, but the presence of bowel gas or obesity may limit its usefulness. CT and MRI angiography are noninvasive imaging modalities used for a correct and complete evaluation of the aortic aneurysms: location, extension, size, shape, contours, content, walls, and complications. Page 2 of 27

3 Multidetector CT angiography (MDCTA) is a faster procedure used to detect and localize the aneurysm and can provide superior three-dimensional details for the complications, useful in surgical endovascular repair (5). Common indications include abdominal aortic aneurysm, aortic dissection/rupture, and the involvement of splanchnic arteries, such as visceral artery aneurysm (renal, splenic or iliac artery aneurysm) (6). MR angiography (MRA) is indicated in young or allergic patients and in selected patients with renal insufficiency. Also MRA has a better accuracy for assessment of the proximal and distal extesion of the AAA, the visceral- branch involvement, the mural pathology and internal constituents of the aneurysm (8). Angiography is often used as preoperative evaluation for demonstrating visceral-branch involvement and variations in vascular anatomy, but it can underestimate both the size and extent of thrombus-filled aneurysms because only the patent lumen is opacified (7). Imaging findings. Type of aneurysm. Most abdominal aortic aneurysms (AAA) are true aneurysms. A true aortic aneurysm is a localized dilatation of the aorta caused by weakening of its wall; it involves all three layers (intima, media, and adventitia) of the arterial wall, while a pseudoaneurysm (false aneurysm) is a collection of flowing blood that communicates with the arterial lumen but is not enclosed by the normal vessel wall; it is contained only by the adventitia or surrounding soft tissue (4). Location. The AAA location (Table 1 on page 4) could be: infrarenal - most common, juxtarenal, suprarenal. Shape. The shape of an AAA (Table 1 on page 4) is usualy described as being: fusiform, frequently diagnosed in our clinic at CT angioraphy, used for patients with cardiac or vascular condition, or saccular. Page 3 of 27

4 Complications. The most common complications of AAA are dissection of the aneurysm and rupture, that increases with the size of the aneurysm (diameter >10 cm) (9) and can lead to retroperitoneal leakage, intraperitoneal or retroperitoneal hemmorrhage and retroperitoneal hematoma. Saccular aneurysms have a higher risk of rupture (5). Images for this section: Table 1: Classifications of the AAA according to type, locations, shape and complications, correlated to our department experience (126 cases of AAA since 2005 ). The most common aspect was that of infrarenal fusiform AAA with parietal thrombosis. Page 4 of 27

5 Imaging findings OR Procedure details Material Retrospective study since 2005: we examined about 126 admitted patients (Table 1 on page 8) for aortic evaluation, in most of the cases using MDCTA for diagnosing AAA and their associated complications. Some of the AAA findings were detected using CT or MR examination for abdominal or pelvic pathology. Age of patients was between 50 and 80 years, with a men dominance (85%). Methods CT protocol. In the CT evaluation we used a mono-slice CT system and a 16-slice MDCT system, performing native and postcontrast biphasic examination, with thickness of 5 mm per slice with reconstructed images of 1,5 mm per slice for 16-slice MDCT system. The scan was triggered via bolus tracking. Patients received 1,5 ml/kgc of iodinated nonionic contrast medium (370 mgi/ml), injected intravenously at a rate of 3-4 ml/s via a power injector. The average radiation dose assessment for the abdominal aorta was ~ 1,5-2,5 msv. MRA protocol. MRA imaging was performed using a 1,5-T magnet with Torsopa coil and three-plane localiser. The sequences used (with slice thickness 7 mm and spacing 1 mm) were: - axial T2 FSE FS; - axial/coronal T1 FSPGR Fat Sat; - 3D T1 FSPGR (Smart prep); - then we performed gadolinium-enhanced imaging (0,1 ml/kgc Gd-BOPTA); - axial/coronal T1 FSPGR after Gadolinium. MRA was used especially for young patiens or for patiens allergic to iodined contrast media or with renal failure. Most of the cases of AAA examined (78%) were diagnosed incidentally, using MR imaging for liver or kidney disese. Page 5 of 27

6 CT and MRI reconstructions. MPR (multiplanar reformatations) were used for reformatting and reconstructing the images from the axial image data in three planes, coronal, sagittal and oblique, for a better location and shape of the dilatations. MIP (maximum intensity projection) was used, mostly in MDCT, to define de volume of the true aortic lumen, especially for the AAAs associated with thrombosis (partial or total). It was also suitable to detect the involvement of the splachnic and iliac arteries, their emergencies and perfusion. 3Ds (surface rendering) provided realistical three-dimensional wiew of the abdominal aorta and the exact size, location and shape of the aneurysm, and accurate details of the surface. Imaging analysis. For both techniques imaging analysis consisted in the evaluation of the type of the aneurysm, localization, length, involvement or stenosis of splanchnic arteries, involvement of aortic bifurcation and iliac arteries, intraluminal thrombus, dissection, wall abnormalities, signs of rupture, complications (inflammatory changes, periaortic hematoma, perianeurysms fibrosis). For optimal interpretation of the scans in both methods, we used coronal, sagittal and oblique planes 2D MPR, MIP and 3D VRT reconstructions. Imaging findings. We diagnosed various types and shapes of AAA and their direct complications or complications appeared after surgical repair, using MIP, 2D MPR and 3D VRT reconstruction for better details of the images. Type: Most of the examined patients had true AAA (95%), caused by atherosclerosis, but some of them were diagnosed with pseudoaneurysm of the abdominal aorta (5%) of different sizes, from small (12 mm) to large dilatations (12 cm) in our study. Location and shape: According to the number of cases specified in the table 1, in most of the cases the aortic aneurysms were fusiform, located infrarenal (about 78% of cases investigated in our department) (Fig. 1 on page 8). In a small amount of cases the AAA was located juxtarenal (Fig. 2 on page 9 ) or suprarenal (Fig. 3 on page 10). The shape of an AAA is usualy, fusiform or saccular (Fig. 4 on page 11, Fig. 5 on page 12). Page 6 of 27

7 The aneurysms shape is important because the saccular shape has a worse prognosis, due to the higher risk of rupture than the fusiform one. The size of an AAA is variable, from small to medium and large (Fig. 6 on page 13). Multiple aneurysmal dilatations: One of the particular AAAs diagnosed in our clinic were the multiple successive dilatations, separated by short or long parts of not dilated aortic lumen (Fig. 7 on page 14 and Fig. 8 on page 15). Complications: Thrombosis. Many of the AAAs had associated parietal thrombosis, mostly from minimal to large circumferential thrombosis (Fig. 9 on page 16), in some cases extended to the splachnic arteries and the common iliac branches. Rarely, the diagnosed aneurysms were totaly thrombosed (Fig. 10 on page 17). Dissection. In several cases of AAA the intimal layer of the dilated wall was dissected, forming o false aortic lumen (Fig. 11 on page 18 and Fig. 12 on page 19). The arterial phase of the MDCTA evaluation was also used to distinguish the true aortic lumen (contrast enhancement in the arterial phase) from the false lumen in the aortic dissection (Fig. 12 on page 19) and to detect the involvement of the splanchnic arteries and the extension to the aortic bifurcation and iliac arteries. In these cases we have carefully evaluated the perfusion in the main branches of the aorta, because in some cases these emerged from the false aortic lumen. Rupture of the aneurysms, that usually associated a peritoneal or retroperitoneal massive hematic collection (Fig. 13 on page 20), or a retroperitoneal chronic hematoma. Active bleeding in ruptured aneurysms can be demonstrated in the arterial phase, detecting the active extravasation of contrast material from the aortic lumen in the arterial phase, but also by the presence of hemorrhagic collections, as seen in our cases. Ulcerations. One of rarely detected complications were the ulcerations of the aortic wall (Fig. 13 on page 20), described as additional images of the aortic lumen. Fistula. Another interesting finding of associated pathology was a case of large AAA with circumferential thrombosis, with a fistula between the abdominal aorta and IVC (simultaneous contrast enhancement of both lumena in the arterial phase) that was dissected (Fig. 14 on page 21). Differential diagnosis. Pseudoaneurysms. A true AAA can be misdiagnosed with a pseudoaneurysm. Saccular aneurysms can be distinguished from the pseudoaneurysmal formation by the calcifications of the outer wall of the aneurysm (Fig. 15 on page 22 and Fig. 18 Page 7 of 27

8 on page ). AAAs with irregular parietal thrombus or intramural hematoma can be misdiagnosed with a sacular pseudoaneurysm developed by a penetrating ulcer of the aortic wall, that can be demostrated by the focal aortic wall thickening and ulcerated plaque (5). Retroperitoneal masses. Also, a variety of retroperitoneal masses, located adjacent to the abdominal aorta, can be confused with areas of aneurysmal expansion (Fig. 17 on page 24). This includes lymphadenopathies, perianeurysmal fibrosis, ganglioneuroma, paraganglioma, sarcomas (leiomyosarcoma), metastases (5). Images for this section: Table 1: Classifications of the AAA according to type, locations, shape and complications, correlated to our department experience (126 cases of AAA since 2005 ). The most common aspect was that of infrarenal fusiform AAA with parietal thrombosis. Page 8 of 27

9 Fig. 1: Infrarenal AAA: Male, 65 years old. Fusiform, small infrarenal AAA, without complications (arrows). Page 9 of 27

10 Fig. 2: Juxtarenal AAA: Male, 58 years old. MIP projection image obtained from MR angiography with Gadolinium of a juxtarenal, sacular AAA (red star). The celiac artery and the superior mesenteric artery emerge from the dilated aortic lumen (yellow arrows). Right and left renal arteries also emerge from the dilated lumen (blue arrows). Page 10 of 27

11 Fig. 3: Suprarenal AAA: Male, 67 years old. CT angiography with iodinated non ionic contrast : suprarenal AAA of a sinuous abdominal aorta, with associated parietal thrombosis (white star). Celiac artery and the superior mesenteric artery emerge from the real aortic lumen (yellow arrow). Multiples soft and calcified aortic plaques involving especially the infrarenal aorta. Page 11 of 27

12 Fig. 4: Fusiform AAA: Male, 68 years old. CT angiography: infrarenal fusiform AAA, associating partial thrombosis (white star) and multiple parietal calcifications, with extension to both common iliac artery (yellow arrow). Note the importance of the MPR reconstructions (in coronal and sagittal plane) to evaluate the length of the aneurysm, the walls and the lumen of the aorta. Page 12 of 27

13 Fig. 5: Saccular AAA: Male, 79 years old. Pseudosaccular AAA (red arows), located infrarenal, with partial thrombosis (white star) and multiple parietal calcifications. Note the importance of source images analysis to better evaluate the abnormalities involving the wall and the aortic lumen. Page 13 of 27

14 Fig. 6: Different sizes of AAA. Three cases of AAA in different sizes (red arrows), from small (a) to medium (b) and large (c). Page 14 of 27

15 Fig. 7: Multiple fusiform AAA: Female, 63 years old. Multiple successive, infrarenal, fusiform AAA, of different sizes, (blue star). Page 15 of 27

16 Fig. 8: Multiple saccular AAA: Male, 55 years old. CT angiography: multiple saccular AAA (red star), located juxtarenal and bellow the renal arteries (renal arteries-red arrow), patially thrombosed. Celiac and superior mesenteric artery emerge from the true lumen (yellow arrows). Page 16 of 27

17 Fig. 9: Parietal partial thrombosis: Male, 65 years old. Gd-MR angiography. Fusiform, infrarenal AAA, partial thrombosed (white star), extended to the left iliac artery. Total obstruction of the right common iliac artery (blue arrow). Aneurysmal dilatation of the left common iliac artery (red star), with parietal thrombosis. MIP projection image obtained from MR angiography, showing the circulating lumen. Page 17 of 27

18 Fig. 10: Total thrombosis of AAA: Male, 56 years old. Total thrombosis of a small fusiform infrarenal AAA (MPR projections in coronal and sagittal plane shows absence of contrast enhancement of the infrarenal aorta). Note the calcified dissection flap atheroma plaques - yellow arrow). Normal enhancement of the renal arteries. Page 18 of 27

19 Fig. 11: Small saccular suprarenal AAA and dissection (red arrow) in a male, 67 years old. Page 19 of 27

20 Fig. 12: Important abdominal aortic calcified atheromatosis and dissection, in a male, 54 years old. CT angiography-fusiform AAA, dissected (calcified intimal flap and multiple aortic walls calcifications - red arrows), with important atheromatosis (MIP, VRT reconstruction) partially thrombosed (white star). The celiac artery and the mesenteric artery emerge from the true lumen of the aorta (blue arrows). Page 20 of 27

21 Fig. 13: Large fusiform infrarenal AAA, partially thrombosed (red star), ruptured with large retroperitoneal hematoma (blue arrows), in a male, 80 years old. Note the existence of multiple ulcerrations (enlarged details, red arrows). Page 21 of 27

22 Fig. 14: Fistula: Male, 65 years old. Large infrarenal, fusiform AAA, with parietal large thrombosis. Dissection flap in the IVC (blue arrow). Vascular fistula (red arrow) between the aortic lumen (red star) and IVC (blue star), with simultaneous arterial contrast enhancement in both lumena. Right retroperitoneal dense accumulation (yellow arrow). Page 22 of 27

23 Fig. 15: Pseudoaneurysm: Male, 62 years old. Small pseudoaneurysmal dilatation (red arrow) of the posterior aortic wall (red star), located suprarenal (left renal artery - yellow arrow), ruptured, associating a chronic periaortic and retroaortic hematoma (blue arrows). Page 23 of 27

24 Fig. 16: Large pseudoaneurysm: Male, 52 years old. Large pseudoaneurysmal hematic retroperitoneal extravasation, associating active bleeding from the abdominal aorta (extravasation of iodinated contrast media - red arrow) and chronic hematoma in a case of ruptured infrarenal abdominal aorta (red star- true aortic lumen). Page 24 of 27

25 Fig. 17: Differential diagnosis-retroperitoneal mass: A case of a 56 years old male that had surgery for an urothelial tumour. Retroperitoneal tumour mass (yellow arrows), located adjacent to the inferior part of the abdominal aorta, the aortic bifurcation and the left common iliac artery (red arrows), that appears like a pseudoaneurysmal dilatation of the aorta, but after gadolinium, it was diagnosed as a paraortic tumoral mass, with different enhancement of gadolinium than the aortic lumen. Page 25 of 27

26 Conclusion MDCT angiography and MR-angiography have to be used in aortic abdominal aneurysms evaluation according to the clinic and biological context or patient characteristics. CT angiography is recommended in emergencies cases and for unstable patients becouse is a very fast method, with high accuracy in evaluating aneurysmal lesions and their complications. MRA is used especially for young or allergic patients and to characterize aortic wall changes like parietal hematoma or parietal ulcer. Imaging evaluation of the AAA, using MDCTA and MRA techniques, including two-dimensional and three-dimensional image processing of the findings, is essential in establishing an accurate diagnosis, the severity of the aneurysm and the associated complications. These noninvasive techniques increase significantly the possibility of a proper clinical management and preoperative evaluation of affected patients. References 1. Pearce WH, Rowe VL. Abdominal Aortic Aneurysm, Medscape reference, Wilmink TB, Quick CR, "The association between cigarette smoking and abdominal aortic aneurysms". J Vasc Surg, Day NE, 1999 Dec;30(6):p Treska V. et al.:aneuryzma b#išní aorty, Prague, 1999, ISBN Rakita D, Newatia A, Hines JJ, Siegel DN, Friedman B. Spectrum of CT Findings in Rupture and Impending Rupture of Abdominal Aortic Aneurysms, Radiographics, 2007, 27, Prokop M, Galanski M. Spiral and Multislice Computed Tomography of the Body, Springer , 54-55, , Pelberg R, Mazur W.Vascular CT Angiography Manual, Thieme-2010, p LaRoy LL, Cormier PJ, Matalon TA, Patel SK, Turner DA, Silver B. Imaging of abdominal aortic aneurysms, AJR,1989, 152 (4): Amparo EG, Higgins CB, Hoddick W, Hricak H, Kerlan RK, Ring EJ, Kaufman L, Hedgecock MW. Magnetic resonance imaging of aortic disease, preliminary results, AJR, 1984, 143 (6), Page 26 of 27

27 Personal Information Radiology and Medical Imaging Department of Fundeni Clinical Institute, Bucharest, Romania University of General Medicine and Pharmacy "Carol Davila" Page 27 of 27