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Erschienen in:
04.05.2016 | Classics in Abdominal Imaging
The “beak” sign
Erschienen in: Abdominal Radiology | Ausgabe 6/2016
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A bird’s beak (Fig. 1) metaphorically describes the angular extensions of normal tissue adjacent to a slowly growing mass in a solid organ [1]. Also known as the “claw” sign, it originally was applied to the appearance of a simple renal cyst as seen at excretory urography (EU), referring to the tapering of the renal parenchyma along the margin of the cyst, recalling a bird’s beak (Fig. 2) [1, 2]. The appearance can, however, be seen with any slowly growing mass in a solid organ; the presence of the beak or claw sign offers a clue that the mass indeed arises from that organ rather than from a surrounding structure [3]. Although initially described for EU, the sign can be seen with other imaging modalities, including ultrasound (Fig. 3), CT (Fig. 4), and MRI (Fig. 5) [2].
Fig. 1
The multicolored beak of a puffin [4]
Fig. 2
EU tomographic image shows the tapered appearance of the renal parenchyma (yellow arrows) as it wraps around the edge of a cyst (blue arrow), reminiscent of a bird’s curved beak, consistent with an accomodating renal response to the slowly growing renal cyst
Fig. 3
Ultrasound demonstrates the angular extension of normal renal tissue (yellow arrows) surrounding the margin of a renal cyst (blue arrow)
Fig. 4
Axial contrast-enhanced CT image shows a simple cyst (blue arrow) with the corresponding “beak” appearance of the renal parenchyma (yellow arrows) at the margins of the cyst
Fig. 5
Axial T2-weighted MRI image shows a cyst (blue arrow) arising from the left kidney, with the characteristic “beak” of surrounding normal tissue (yellow arrows)
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