Twinkle artifact in renal ultrasound, is it a solid point for the diagnosis of renal stone in children?

Background: Twinkle artifact, also known as color Doppler comet-tail artifact,occurs behind very strong, granular, and irregular reflecting interfaces such ascrystals, stones, or calcification. This is visualized as a random mixture of red andblue pixels in the high-frequency shift spectrum located deep to the interface. Studyresults have suggested that the sonographic twinkling artifact may aid in the detectionof renal stones with a variety of reference standard imaging modalities, includingabdominal radiography, excretory urography, gray-scale sonography, and CT. Material andmethods: Our retrospective observational study included children who had undergoneabdomen/renal ultrasound for kidneys stones in our radiology department between 2013 and2019. Presence of the twinkle artifact, and stone numbers and sizes were documented. CTexaminations done <3 months prior to or after US were retrospectively assessed toconfirm the presence of kidney stones as a reference standard. Results: Thirty-threeabdominal renal US scans of 33 patients (21 males, 12 females) fulfilled the entrycriteria. The interval between the US and CT was <3 months for all patients. Themedian overall age of the patients was 4 years (IQR: 3.125, range: 1– 165 months), Themedian number of days between the US and CT was 13 (IQR: 26, range: 0–81 days). USdetected 33 hyperechoic foci suspected to be stones; 26 were confirmed as true positive(i.e. showed the twinkle artifact and were seen in CT), 4 were false positive (showedthe twinkle artifact but were not seen in CT), and 3 were false negative (did not showthe twinkle artifact but were seen in CT). The overall median stone size was 2 mm in theright kidney, and 5 mm in the left kidney (IQR: 6,11 mm), respectively. Twinkle artifactsensitivity was found to be 89.7% (95% CI 39.574%–90%). The twinkle artifact wasassessed in all true-positive stones, determining a relatively high PPV of 26/29 (86.7%)for the twinkle artifact. The twinkle artifact was not dependent on stone size.Specificity for the twinkle artifact could not be calculated due to a lack of truenegatives. Conclusion: The twinkle artifact is a sensitive US tool for detectingpediatric kidney and ureter stones, but with a small risk of false positivefindings.