Case 9799 Stanford type A aortic dissection: US and CT findings Accogli S, Aringhieri G, Scalise P, Angelini G, Pancrazi F, Bemi P, Bartolozzi C Department of Diagnostic and Interventional Radiology, University Hospital of Pisa, Italy. Section: Cardiovascular Published: 2012, Mar. 13 Patient: 67 year(s), female Clinical History A 67-year-old female patient presented to the emergency room of our hospital complaining of 3 days pain located in left iliac fossa; an abdomen ultrasound (US) evaluation was requested. Imaging Findings Abdominal US and Colour-Doppler (CDUS) imaging detected a suprarenal aortic aneurysm of 37 mm with suspect of dissection [Fig. 1]. Emergency spiral CT (basal [Fig. 2] and contrast-enhanced [Fig. 3]) confirmed a dissecting thoraco-abdominal aortic aneurysm beginning in the ascending aorta just above the aortic valve (Standford type A) involving the entire thoracic and part of abdominal aorta, ending just proximally to the origin of celiac artery. Also epiaortic trunks were involved in dissection. The widest diameters measured 70 mm in the ascending thoracic aorta, 53 mm in the aortic arch, 47 mm in descending aorta and 37 mm in suprarenal abdominal aorta. At CT evaluation, ectasia of abdominal aorta and both common iliac arteries (17 mm right and 16 mm left) was depicted. Moreover, origin of coeliac trunk and left renal artery from false lumen was evidenced [Fig. 4]. Discussion Acute Aortic Dissection (AAD) is one of the most dramatic cardiovascular emergencies [1], often with a fatal outcome [2], which derives from a spontaneous longitudinal separation of the aortic intima and adventitia, caused by blood-flow gaining access to and splitting the media of the aortic
wall [3]. It is termed acute if diagnosed within 14 days after symptoms onset, chronic if later [4]. Risk factors include hypertension, connective tissue disorders (Marfan syndrome, cystic medial necrosis, Ehlers-Danlos syndrome), aortic stenosis or coartation, bicuspid aortic valve and pregnancy. Clinical manifestations usually are low back pain, haemodynamic alterations, signs of ischaemia resulting from the involvement of visceral vessels or iliac-femoral vascular axis. Stanford classification divides AAD in type A (60%, involving the ascending aorta) and B (40%, beginning distally from subclavian artery take-off) [1]. In type A, the dissection flap usually begins close to the aortic root and extends with a cranio-caudal spiral progression. US-imaging allows the identification of the dissection flap, which appears as a hyperechoic septum dividing the lumen into two compartments, but does not allow a complete preoperative planning, expecially neither differentiating between true and false lumen nor from which lumen major visceral branches originate. Multidetector-CT allows AAD diagnosis with a sensitivity and specificity of nearly 100%, enabling: -differential diagnosis between Stanford type A-B; -evaluation of visceral vessels involvement; -study of intimal flap; -distinguishing true from false lumen. At CT true lumen is identified by: -location cranially on the external side of aortic arch; -lower diameter respect to the false lumen, eventually compressed by false lumen; -surrounding by intimal calcification if present; -earlier enhancement after contrast injection (conversely to false lumen, where the slower flow determines delayed opacification); -frequent circular profile; -absence of cobweb sign, beak sign and thrombosis (typical of false lumen). Multidetector-CT is particularly useful in case of emergency: it allows imaging of the entire aorta with rapid acquisition and data reconstruction, enabling early recognition and characterisation of aortic dissection, as well as determination of any associated complications. This is essential to optimise surgical management and improve clinical outcomes. Contrast-enhanced MR-angiography is accurate and noninvasive, it should be avoided in unstable patients due to longer acquisition-time and difficulty in monitoring. Moreover, calcification of the arterial wall or intimal flap might not be visualised. Type A AAD requires promptly open or endovascular surgical intervention [2] in order to avoid the most common complications such as occlusion of the coronary or supraaortic vessels, severe aortic insufficiency with acute heart failure, haemopericardium and cardiac tamponade [1]. Final Diagnosis Stanford type A aortic dissection. Differential Diagnosis List
Abdominal aortic aneurysm, Stanford type B aortic dissection, Pancreatitis, Mesenteric ischaemia, Cholecystitis, Myocardial infarction, Pericarditis, Pulmonary thromboembolism, Thoracic osteochondritis Figures Figure 1 US imaging: B-mode and color-doppler B-mode ultrasound axial scan of epigastric region showing suprarenal aortic aneurysm (37 mm) and a thin hyperechoic band that separates two different lumens, which assumes the suspect of dissection. Imaging Technique: Ultrasound;
B-mode ultrasound axial scan of the abdominal region (distally than Fig.1 a) showing the diameter of the suprarenal abdominal aortic aneurysm of 37 mm. Imaging Technique: Ultrasound; B-mode ultrasound axial scan of the abdominal region (distally than Fig.1 b) showing calcification of the intimal flap. Imaging Technique: Ultrasound;
Colour-Doppler ultrasound axial scan showing blood flow within the smaller lumen of the vessel. Imaging Technique: Ultrasound-Colour Doppler; B-mode ultrasound longitudinal scan showing intimal flap and large vascular wall calcifications.
Imaging Technique: Ultrasound; Colour-Doppler ultrasound longitudinal scan showing blood flow between intimal flap and posterior aortic vascular wall. Imaging Technique: Ultrasound-Colour Doppler; Special Focus: Aneurysms; Figure 2 CT
Axial Basal CT showing aneurysm of ascending aorta (diameter 70 mm). Imaging Technique: CT; Special Focus: Aneurysms; Axial Basal CT showing aneurysm of aortic arch (diameter 53 mm). Imaging Technique: CT; Special Focus: Aneurysms;
Axial basal CT showing dilation of abdominal aorta with calcification inside. Imaging Technique: CT; Figure 3 Contrast-enhanced CT Contrast-enhanced arterial phase axial CT showing dissection that involves also superior mesenteric artery, which appears to take off from true lumen.
Imaging Technique: CT-Angiography; Contrast-enhanced arterial phase axial CT showing dissection extending to the left external iliac artery. Imaging Technique: CT-Angiography; Contrast-enhanced arterial phase axial CT showing the origin of celiac trunk from false
lumen of the dissecting aorta. Imaging Technique: CT-Angiography; Contrast-enhanced venous phase axial CT confirming US-imaging results of calcification of the intimal flap. Imaging Technique: CT; Figure 4 Multi Planar Reformation (MPR)
Sagittal projection in MPR of the Stanford type A aortic dissecting aneurysm showing the intimal flap beginning close to the aortic root and extending with a cranio-caudal spiral progression to abdominal tract. Imaging Technique: Image manipulation / Reconstruction; Procedure: Computer Applications-Detection, diagnosis; Coronal projection in MPR of the Stanford type A aortic dissecting aneurysm involving anonymous trunk and left common carotid artery. Imaging Technique: Image manipulation / Reconstruction; Procedure: Computer Applications-Detection, diagnosis;
Coronal projection in MPR of the Stanford type A aortic dissecting aneurysm showing the intimal flap extending with a cranio-caudal spiral progression to abdominal tract and left renal artery arising from false lumen. Imaging Technique: Image manipulation / Reconstruction; Procedure: Computer Applications-3D; MPR CT image showing aortic dissection involving the right common iliac artery. Imaging Technique: Image manipulation / Reconstruction; Procedure: Computer Applications-Detection, diagnosis;
MPR CT image showing aortic dissection involving the left external iliac artery. Imaging Technique: Image manipulation / Reconstruction; Procedure: Computer Applications-Detection, diagnosis; MeSH Aortic Diseases [C14.907.109] Emergency Medical Services [N02.421.297] Services specifically designed, staffed, and equipped for the emergency care of patients. Aneurysm, Dissecting [C14.907.055.050] Splitting or dissection of an arterial wall by blood entering through an intimal tear or by interstitial hemorrhage. It is most common in the aorta. References [1] Sebastià C, Pallisa E, Quiroga S, Alvarez-Castells A, Dominguez R, Evangelista A (1999) Aortic Dissection: Diagnosis and Follow-up with Helical CT RadioGraphics 19:45-60 [2] McMahon MA, Squirrell CA (2010) Multidetector CT of Aortic Dissection: A Pictorial Review RadioGraphics 30:445-460 [3] Dähnert W (2003) Cardiovascular disorders: aortic dissection. Radiology review Radiology review manual 5th ed. Philadelphia 607-609
[4] Prêtre R, Von Segesser LK (1997) Aortic dissection The Lancet 349:1461-4 Citation Accogli S, Aringhieri G, Scalise P, Angelini G, Pancrazi F, Bemi P, Bartolozzi C Department of Diagnostic and Interventional Radiology, University Hospital of Pisa, Italy. (2012, Mar. 13) Stanford type A aortic dissection: US and CT findings {Online} URL: http://www.eurorad.org/case.php?id=9799