Radiologia

MDCT Evaluation o f A c u t e Ao r t i c S y n d ro m e
Seung Min Yoo, MD, PhDa, Hwa Yeon Lee, MD, PhDb, Charles S. White, MDc,*
KEYWORDS
 Acute aortic syndrome  Aortic dissection  Intramural hematoma  Penetrating atherosclerotic ulcer  Multidetector CT (MDCT)

Acute aortic syndrome (AAS) comprises aortic dissection (AD), intramural hematoma (IMH), penetrating atherosclerotic ulcer(PAU), and unstable aortic aneurysm. Because the highest mortality of AAS, particularly AD, occurs during the first 48 hours after onset of symptoms, prompt diagnosis and immediate initiation of appropriate therapy is essential for a favorable outcome.1 Unfortunately, several studies have reported that a delay in diagnosis of more than 24 hours after admission occurs in up to 39% of patients withAD.2,3 This is mainly because of a significant overlap of clinical symptoms between AAS and acute coronary syndrome (ACS) or pulmonary embolism (PE). In addition, the annual incidence of AAS, ACS, and PE has been estimated at 0.5 to 3.0, 440.0, and 69.0 per 100,000 in the United States, respectively.4,5 This relatively rare occurrence of AAS compared with ACS and PE increases the likelihood of delayeddiagnosis or misdiagnosis of AAS as ACS or PE. Although radiologists are not directly involved with history taking or physical examination of patients with suspicious AAS, a precise understanding of both the pretest probability and typical clinical symptoms and signs of AAS is valuable for radiologists to get the broadest perspective of AAS. Current multidetector CT (MDCT) equipped withstate-of-the art tube and detector technology, and

optimal temporal and spatial resolution has become widely available globally. With appropriately obtained MDCT data in patients who have findings suspicious for AAS, the diagnostic accuracy of MDCT is nearly 100%. This article provides a summary of AAS, focusing especially on MDCT technique and findings of AAS, as well as recent concepts regarding thesubtypes of AAS, consisting of AD, IMH, PAU, and unstable aortic aneurysm.

AORTIC DISSECTION Pathogenesis of Aortic Dissection
The exact mechanism of AD still remains unclear.6 AD is characterized by intimal rupture and subsequent formation of a false lumen parallel to the original aortic lumen. An entry tear is likely to be a primary event for development of most AD. In some cases, intramuralhemorrhage in the media followed by intimal rupture may also be an initiating event. Most patients with AD have hypertension. The most common sites of entry tear are the right lateral wall of the ascending aorta and the descending aorta just distal to the left subclavian artery, where the shearing stress against the aortic wall generated by hypertensive blood flow is maximal. Once an entry tear ismade, propagation of AD ensues along the aortic lumen, either in an

a Department of Diagnostic Radiology, 351 Yatop-dong Bundang-gu, CHA Medical University Hospital, Bundang 463-712, Korea b Department of Diagnostic Radiology, 65-207 Hangang-ro 3 ga Youngsan-gu, Chung-Ang University College of Medicine, Seoul 140-757, Korea c Department of Diagnostic Radiology, 22 S. Greene St, University ofMaryland, Baltimore, MD 21201, USA * Corresponding author. E-mail address: cwhite@umm.edu (C.S. White).

Radiol Clin N Am 48 (2010) 67–83 doi:10.1016/j.rcl.2009.09.006 0033-8389/09/$ – see front matter ª 2010 Elsevier Inc. All rights reserved.

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Yoo et al
antegrade or retrograde fashion. When an ascending aortic dissection propagates into the aortic arch anddescending aorta, the dissection often extends along the greater curvature of the aortic arch, resulting in frequent involvement of aortic arch branches (Fig. 1).7 The term intimal flap is a misnomer. As the dissection flap is composed of intima and the inner two-thirds of media, intimomedial flap is a more appropriate terminology. The thickness of the outer wall of false lumen is only one-third...