Renal duplication artefacts in ultrasound imaging

A duplication artefact is sometimes encountered on ultrasound examination of the left kidney. It is caused by sound beam refraction between the spleen and adjacent fat. The purpose of this study was to analyse the frequency and types of such artefacts, and examine their physical background. The examiner searched for a left renal duplication artefact in 150 unselected abdominal ultrasound studies. A disturbed contour of the left kidney could be formed in 34 of 123 patients in whom the spleen was in the image without covering the kidney completely. An artefact was seen significantly more often when the lower pole of the spleen was rounded (30/87) than when it was wedge shaped (4/36) (p < 0.02). The artefacts could be categorized into complete upper pole duplication (n = 4), incomplete upper pole duplication (n = 14) and bayonet artefact (n = 16). The thickness of the renal cortex appeared reduced with upper pole duplication artefacts owing to a geometric image compression, which could also be seen in an in vitro experiment. Left renal duplication artefacts are not rare when the upper part of the kidney is examined by ultrasound through the spleen.