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.
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].
Acute Aortic Dissection (AAD) is one of the most dramatic cardiovascular emergencies , often with a fatal outcome , 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 . It is termed acute if diagnosed within 14 days after symptoms onset, chronic if later .
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) .
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  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 .
Differential Diagnosis List
Stanford type A aortic dissection.
Abdominal aortic aneurysm
Stanford type B aortic dissection
Stanford type A aortic dissection.