Vesicoureteric junction calculus with twinkling artifact
Vague lower abdominal pain on the right side radiating from the lower lumbar region to the scrotum.
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Ultrasound images show that the bladder is partially filled with a hyperechoic foci in the right vesico ureteric junction (VUJ) with distal shadowing on B mode. The colour Doppler study shows twinkling artifact posterior to the hyperechoic foci suggesting it as a calculus. Colour Doppler shows continuous slow ureteric jet on the right side in comparison with the intermittent ureteric jet on the left side and B mode images of the right kidney appears relatively normal without dilated pelvicalyceal system suggestive of non obstructive right VUJ calculus.
Twinkling artifact is a colour phenomenon which imitates turbulent flow, visible behind a strongly reflecting interface on a colour Doppler examination. It manifests as a colour signal but without real flow behind the structures. This artifact has been described behind calcifications in various tissues.
Presence of this artifact is beneficial in cases of detection of urinary tract stones with indistinct echogenicity and poor posterior acoustic shadowing.
However, twinkling artifact can also be a source of confusion. For example, in prenatal fetal scans it can imitate aberrant vessels or flows behind echogenic structures or give the impression of cardiac activity in fetal demise.
Because this artifact is dependent on ultrasound machine settings it is possible to distinguish it from real vessels by changing some parameters. For instance, when the focal zone is above the source of the artifact (such as a urinary stone) the artifact disappears, but when the focal zone is under the hyperechoic area twinkling occurs. This could be an easy distinguishing maneuver in assessment of this phenomenon.
In our experience reviewing 120 cases we found out that not only changing the focal zone increases the specificity but also adjusting the pulse repetition frequency significantly increased the specificity. We also had difficulty differentiating subtle calculus from artifact generated by excessive bowel gas which is a case more often in than not in the day to day practice.