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Erschienen in:
01.08.2015 | Classics in Abdominal Imaging
The onion ring sign
Erschienen in: Abdominal Radiology | Ausgabe 6/2015
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Cut an onion down the middle and the internal pattern of concentric rings is obvious (Fig. 1). The pattern is also typical of the ultrasound appearance of some testicular epidermoid cysts, where it is known as the “onion ring” sign [1]. The appearance of alternating rings of hypo- and hyperechogenicity, first described at sonography (Fig. 2), corresponds closely to the cross-sectional pathologic appearance, where layers of lamellated keratin are seen [2, 3]. These intratesticular lesions are usually round or oval, and typically sharply separated from surrounding testicular parenchyma. They sometimes have a calcified margin or an echogenic center surrounded by a thicker, hypoechoic ring where the sonographic findings have been alternatively referred to as a “target” or “bull’s eye” appearance.
Fig. 1
A cut onion demonstrating the characteristic lammelated configuration (Source: www.Shutterstock.com).
Fig. 2
The “onion ring” appearance of a right testicular epidermoid cyst at ultrasound, with concentric hypo- and hyperechogenic rings.
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