What causes the Beak Sign in the aorta on contrast-enhanced CT imaging?
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Answer:
The Beak Sign represents a specific CT finding in aortic dissection that reliably identifies the false lumen. It appears as an acute angle formed between the dissection intimal flap and the outer aortic wall on axial cross-section. The false lumen characteristically wedges around the true lumen due to permanent systolic pressure, creating this distinctive angular configuration. The space formed by this acute angle can be filled with contrast-enhanced blood or hematoma. The Beak Sign is present in all cases of both acute and chronic aortic dissection and is exclusively found in the false lumen, making it the single most useful indicator for distinguishing the false from the true lumen. This sign is generally easily identified on CT imaging and has proven to be more reliable than other differentiating features such as outer wall calcification, eccentric flap calcification, or intraluminal thrombus.
Why is it called so?:
The sign is named “Beak Sign” because the acute angle formed at the edge of the false lumen resembles the sharp, pointed beak of a bird in profile. The wedge-like configuration of the false lumen creating this angular protrusion against the true lumen visually mimics avian morphology, providing an intuitive descriptive term for this radiological finding.
Pathophysiology:
The Beak Sign develops as a direct consequence of the pathophysiological mechanism of aortic dissection. When an intimal tear occurs, blood enters the medial layer creating a false channel. As systolic pressure continuously acts on the dissection flap, the false lumen propagates and expands around the true lumen. A wedge of hematoma forms at the leading edge of the propagating false lumen, cleaving a space as the dissection extends. This hematoma wedge, which is microscopically present in all dissections, manifests on cross-sectional CT imaging as the characteristic acute angle between the flap and the outer aortic wall. This represents the cross-sectional imaging manifestation of the three-dimensional wedge of hematoma driving the dissection.
Other associated named signs:
– Cobweb Sign – fine strands of dissected media tissue forming a web-like cluster within the false lumen
– Mercedes Benz Sign – triple channel appearance due to secondary dissection within one channel
– Wraparound Sign – in the transverse aortic arch, the inner lumen is invariably the true lumen when one lumen wraps around the other
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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