Dominik Fleischmann MD, Presenter: Research support, Siemens AG Research support, General Electric Company

1) Review the pathology, epidemiology, and natural history of acute aortic dissection and its variants. 2) Describe the anatomic classification of classic aortic dissection (Type A versus Type B) and the spectrum of dissection variants, such as limited dissection (limited intimal tear) and it's relation to intramural hematoma (IMH). 3) Explain the imaging strategy and diagnostic information sought in patients with acute aortic syndromes. 4) Present the imaging findings and therapeutic options in patients with complicated dissections and end organ ischemia, such as identification of true versus false lumen flow, and assessment of side branch involvement.

Acute aortic dissections represent a spectrum of diseases. The common pahologic denominator in patients with acute dissection and it's variants is an abnormal medial layer of the aorta ('cystic media necrosis') which can be found in genetic/inherited diseases (e.g. Marfan's), normal aging, but most importantly in patients with severe hypertension. The CT imaging strategy in patients with acute aortic syndrome includes (i) obtaining non-enhanced images to assess for IMH; (ii) to always include the common femoral arteries in the scanning range; and (iii) to consider EKG-gating of the thoracic aorta. Classic aortic dissection is characterized by a separate flow channel (false lumen) within the diseased aortic media, which is separated from the true lumen by an intimo-medial flap. The traditional Stanford classification distinguishes Type A dissections which involve the ascending aorta, from Type B dissections which do not involve the ascending aorta. Both, type A and type B dissections are subclassified with respect to the site of the primary intimal tear. Limited dissection (limited intimal tear) is a rare dissection variant, characterized by a partial-thickness tear of the aortic wall with exposure of underlying media and adventitia, most commonly involving the ascending aorta (Type A). These subtle lesions can be difficult to detect on non-gated scans. Intramural Hematoma is an unspecific imaging finding associated with many acute aortic disorders, and it can be the only manifestation of a dissection variant. Involvement of the ascending aorta (Type A) requires prompt surgical intervention. Type B lesions are treated conservatively unlesscomplicated. Identification of the primary intimal tear, status of true and false lumen perfusion, and side branch involvement is critical in patients with complications and end organ ischemia who are considered for surgical or endovascular stent-graft repair, balloon-fenestration or side branch revascularizatio

www.stanford.edu/~dominikf/RSNA/

Fleischmann, D, Dissection and Variants.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/11000649.html