ª Springer Science+Business Media New York 2014
Abdominal Imaging
Abdom Imaging (2014) DOI: 10.1007/s00261-014-0292-9
The onion ring sign Jonathan M. Day, Raymond B. Dyer Department of Radiology, Wake Forest Baptist Medical Center, Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, 27157, NC, USA
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. Testicular epidermoid cysts are uncommon, accounting for between 1% and 2% of intratesticular tumors. They usually present as palpable, nontender nodules in men aged 20–40 years [3]. The diagnosis of exclusion, when confronted with an intratesticular lesion with similar imaging characteristics, is a primary testicular germ cell tumor. A key feature in differentiating the two lesions is central flow by color Doppler imaging which, if present, would favor a neoplasm, as epidermoid cysts are true cysts that have no internal flow (Fig. 3). Because epidermoid cysts are benign, if correctly identified preoperatively, testicular sparing surgery may be considered [3].
Correspondence to: Jonathan M. Day; email: jonathan.m.day@ gmail.com
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.
J M. Day, R B. Dyer: The onion ring sign
References 1. Malvica R (1993) Epidermoid cyst of the testicle: an unusual sonographic finding. AJR 160:1047–1048 2. Manning MA, Woodward PJ (2010) Testicular epidermoid cysts: sonographic features with clinicopathologic correlation. J Ultrasound Med 29:831–837 3. Loya AG, Said JW, Grant EG (2004) Epidermoid cyst of the testis: radiologic-pathologic correlation. RadioGraphics 24:S243–S246
Fig. 3. Color Doppler ultrasound imaging shows no internal flow in the lesion, an important distinguishing feature of a benign testicular epidermoid cyst.
Abdominal Imaging
Abdom Imaging (2014) DOI: 10.1007/s00261-014-0292-9
The onion ring sign Jonathan M. Day, Raymond B. Dyer Department of Radiology, Wake Forest Baptist Medical Center, Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, 27157, NC, USA
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. Testicular epidermoid cysts are uncommon, accounting for between 1% and 2% of intratesticular tumors. They usually present as palpable, nontender nodules in men aged 20–40 years [3]. The diagnosis of exclusion, when confronted with an intratesticular lesion with similar imaging characteristics, is a primary testicular germ cell tumor. A key feature in differentiating the two lesions is central flow by color Doppler imaging which, if present, would favor a neoplasm, as epidermoid cysts are true cysts that have no internal flow (Fig. 3). Because epidermoid cysts are benign, if correctly identified preoperatively, testicular sparing surgery may be considered [3].
Correspondence to: Jonathan M. Day; email: jonathan.m.day@ gmail.com
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.
J M. Day, R B. Dyer: The onion ring sign
References 1. Malvica R (1993) Epidermoid cyst of the testicle: an unusual sonographic finding. AJR 160:1047–1048 2. Manning MA, Woodward PJ (2010) Testicular epidermoid cysts: sonographic features with clinicopathologic correlation. J Ultrasound Med 29:831–837 3. Loya AG, Said JW, Grant EG (2004) Epidermoid cyst of the testis: radiologic-pathologic correlation. RadioGraphics 24:S243–S246
Fig. 3. Color Doppler ultrasound imaging shows no internal flow in the lesion, an important distinguishing feature of a benign testicular epidermoid cyst.
