Schematic illustration of urinary tract dilation (UTD) classification shows a transverse view of mid/interpolar kidney. a The green arrows indicate acceptable locations for measuring the anteriorposterior renal pelvic diameter, which can be measured anywhere within the renal pelvis bordered by renal parenchyma visualized during prone imaging. Measurements of the extrarenal pelvis should not be included. The largest measurement should be the one used for the purpose of UTD classification. The gray arrow indicates the anteriorposterior diameter of the extrarenal pelvis, which should not be used for UTD classification. The different degrees of calyceal dilation are shown in clockwise fashion. The upper left corner shows normal (NL), where fluid is confined to the pelvis. The upper right corner shows UTD P1 (P1), where there are varying degrees of central calyceal dilation. The lower right corner shows UTD P2 (P2), where there are varying degrees of peripheral calyceal dilation, with fluid cupping around the medullary pyramid. The lower left corner shows UTD P3 (P3), where the renal parenchyma is hyperechoic, cystic and thinned. Although this schematic illustration shows progressive increases in calyceal dilation, note that the definition of UTD P3 is based on abnormal parenchyma or bladder appearance in addition to UTD. b The longitudinal appearances of the UTD classifications are shown in tabular format, with side-by-side US and schematic images. Note that the renal pelvic diameter is not measured in the longitudinal plane. The P1 category demonstrates central calyceal dilation and the P2 category demonstrates peripheral calyceal dilation (arrows). The P3 category shows abnormal parenchymal thickness with cystic changes in the parenchyma
