The 'two-tone' testis

摘要

The term "two-tone" has been applied to the distinctive appearance of an uncommon artifact encountered at testicular ultrasonography, which is reminiscent of a custom paint job on a classic car (Fig. 1). First described in 1995 [1], the two-tone testis is an imaging artifact that characteristically exhibits normal parenchymal echogenicity in the near-field portion of a testicular ultrasound image with hypoechoic parenchymal echogenicity deep to an oblique interface. On color Doppler ultrasound imaging, the oblique interface is shown to be due to a transtesticular artery (Fig. 2). In one report, only 1.6% of a study population that included 1038 patients undergoing testicular ultrasound examination exhibited the two-tone artifact [2]. Importantly, in this same report the artifact was shown to have no relation to the presenting clinical symptoms or other ultrasound findings. The distinctive two-tone appearance of the testicle is proposed to be a byproduct of refractive shadowing and defocusing of the sound beam rather than reflective shadowing [1-3]. The phenomenon is somewhat analogous to a beam of light reflecting and refracting at an air-water interface (Fig. 3). Furthermore, if the artifact was due to reflective shadowing, one would expect the wall of the transtesticular vessel to have strong wall echogenicity, which is not the case with the two-tone testis [2]. Other common anatomic areas in ultrasonography where this refractive type artifact is recognized is the oblique interface of the gallbladder wall or edge of a cyst in a solid organ. Ultimately, it is important for both radiologists and sonographers to recognize that the two-tone artifact is not associated with any pathologic condition.