Beak Sign Paul Moullet, DO and Howard Mann, MD A
C Beak Sign Appearance of the separation between the intima and media layers of the aorta resembling a bird’s beak. Beak sign exclusively appears in the setting of aortic dissection when analyzing vascular architecture.
FIGURE 1. ECG-gated CTA showing the beak sign (solid arrows), with a corresponding schematic demonstrating the location of the beak sign. A, Coronal image showing angulation of intimal/mediastinal interface. B, Axial image of aortic dissection showing beak sign as well as difference in luminal size of false vs. true lumens. C, Schematic showing layers of aorta and location of beak sign.
Appearance: A “birds-beak” of contrast-opaciﬁed blood appears at the mural attachment of the intimomedial ﬂap in the aortic lumen (Fig. 1). When this triangular-shaped region in the false lumen is thrombosed, the beak is “black” in appearance on contrast-enhanced CT. This sign is a useful tool for distinguishing between a false and true lumen during evaluation of an acute or chronic aortic dissection.1 Explanation: Aortic dissection is deﬁned as the disruption of the intima of the aorta allowing bleeding along the wall of the aorta and resulting in formation of two communicating channels.2 The classic dissection results in an intimomedial ﬂap between the two lumens.1,2 The separation of the two layers of the aortic wall results in a point where the layers are still attached in non-circumferential dissections. This intimomedial ﬂap does not extend across the center of the aorta as a linear band. Instead, the septum spirals lengthwise along the aorta forming a convexity toward the false lumen. Discussion: The beak sign is traditionally applied to entities within gastrointestinal radiology, including the beak sign of achalasia and the beak sign of a sigmoid volvulus on barium contrast studies. In the thorax, the beak sign occurs in aortic dissection. In fact, CT has a detection sensitivity and speciﬁcity of up to 100% in one reported series.3 Aortic dissection is the most common of the three acute aortic syndromes. Traditionally, there are two classiﬁcation systems for categorizing aortic dissection: the DeBakey and Stanford classiﬁcations. There are two types of dissections according to the Stanford classiﬁcation: Type A, which involves the ascending aorta and the aortic arch and Type B, which involves the descending aorta. Of the two types of dissection, Type A carries a much higher risk of mortality due to possible involvement of the aortic valve, pericardium, coronary arteries, and cerebral branch vessels.4,5 This type of dissection is a surgical emergency and can only be repaired using an open procedure. Endovascular repair is increasingly being used to repair select Type B lesions.6 In fact, when discussing endovascular repair, a much wider scheme of classiﬁcation should be implemented in order to gauge mortality and therapeutic options. The DISSECT mnemonic has been proposed to supplement the two other classiﬁcation systems to further delineate therapeutic response and mortality.6 The DISSECT mnemonic deﬁnes 6 features of aortic dissection which are: duration of disease; intimal tear location; size of the dissected aorta; segmental extent of aortic involvement; clinical complications of the dissection, and thrombus within the aortic false lumen. If repair of the aortic dissection is to be undertaken, it is also very important to delineate the true and false lumens for planning purposes as well as post procedure assessments. Delineating true from false lumen can be accomplished by recognizing one or more of the following ﬁndings: the location of displaced intimal atherosclerotic calciﬁcations; the relatively large size of the false lumen (except at the aortic root); the cobweb sign of irregular and slender low attenuation structures in the contrast-opaciﬁed false channel likely representing disrupted fragments of mural smooth muscle; evaluating the root of the aorta/aortic valve where the true lumen will always be larger; comparison on ECG-gated CTA for diﬀerences in size of true lumen during systole where the lumen will enlarge and during diastole where the lumen will be compressed; and the beak sign.7 REFERENCES 1. LePage M, Quint L, Sonnad S, et al. Aortic dissection: CT features that distinguish true lumen from false lumen. AJR. 2001;177:207–211. 2. Hiratzka L, Bakris G, Hermann L, et al. 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with thoracic aortic disease. Circulation. 2010;121:297–303. 3. Shiau M, Godoy M, Groot P, et al. Thoracic aorta: acute syndromes. Applied Radiology. 2010;39:1–2. 4. Braverman A. Aortic dissection: prompt diagnosis and emergency treatment are critical. Cleveland Clinic Journal of Medicine. 2011;78:685–696. 5. McMahon M, Squirreell C. Multidetector CT of aortic dissection: a pictorial review. RadioGraphics. 2010;30:445–460. 6. Dake M, Thompson M, Sambeek Mv, et al. DISSECT: a new mnemonic-based approach to the categorization of aortic dissection. European Journal of Vascular and Endovascular Surgery. 2013;46:175–190. 7. Choh N, Choh S, Naikoo B, et al. Images in pediatrics: circumferential aortic dissection. Arch Dis Child. 2008;93:581. The authors declare no conﬂicts of interest. Copyright r 2014 by Lippincott Williams & Wilkins
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J Thorac Imaging
Volume 29, Number 6, November 2014