Dominik Fleischmann MD, Presenter: Speakers Bureau, Bracco Group Speakers Bureau, Siemens AG

1) Reveiw the pathology, epidemiology and natural history of acute aortic dissection. 2) Describe the imaging strategy and diagnostic information sought in patients with acute aortic syndromes. 3) Explain the current anatomic classification of aortic dissection, which is based on both, the origin (primary intimal tear), and the extent (Type A versus Type B) of a dissection. 4) Present the imaging findings and therapeutic options in patients with complicated dissections and end organ ischemia, such as identification of true vs false lumen flow and assessment of side branch involvement.

Acute aortic dissection is a rare, but the most lethal of aortic disorders. The common pathologic denominator in patients with acute dissection is an abnormal medial layer of the aorta ('cystic media necrosis') which can be found in genetic/inherited diseases (e.g. Marfan's) but also 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) including the common femoral arteries in the CTA scanning range to assess the lesion extent and to identify a percutaneous  access route; and (iii) to consider EKG-gating for motion-free static and dynamic evaluation of the thoracic aorta and the aortic root. Accurate anatomic classification of aortic dissection requires that two equally important features are described: The origin (i.e. the site of the primary intimal tear), and the extent (aortic segments involved) of the lesion. The traditional Stanford classification distinguishes between dissections involving the ascending aorta (Type A) from those that do not involve the ascending aorta (Type B). Both, type A and type B dissections are subclassified with respect to the site of the primary intimal tear, which can be located in the ascending aorta, arch, or descending aorta (for type A), or in the arch, or descending aorta (for Type B). Involvement of the ascending aorta (Type A) requires prompt surgical intervention. If the ascending aorta is not involved (Type B) conservative treatment is recommended unless there are complications (persistent or recurrent pain, progression, malperfusion syndromes, rupture). Identification of the primary intimal tear, status of true and false lumen perfusion, and side branch involvement are of critical importance in patients with complications and end organ ischemia (renal, mesenteric, lower extremity) who are considered for surgical repair or endovascular stent-grafting, balloon-fenestration or side branch revscularization. 

Fleischmann, D, The ABCs of Aortic Dissection.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6005792.html