ABSTRACT
<p><b>BACKGROUND</b>The initial classic classification of duplex kidney into complete (two ureters) and incomplete ("Y" shaped ureter) types are based on the ureter status. At the meantime, the features of the upper and lower moieties of duplex kidney were very crucial for appropriate procedure of hemi-nephrectomy, which was most commonly used for addressing the issues caused by a duplex kidney; and recently more applications of laparoscopy were used. In this study, we aimed prudently to propose a new classification based on the features of the upper and lower moieties of duplex kidney.</p><p><b>METHODS</b>Sixty-five children with 83 duplex kidneys were reviewed retrospectively. Based on kidney morphology found in CT urography and surgical findings, duplex kidney was classified into five types.</p><p><b>RESULTS</b>The first was the appendant type (36/83) and its feature was that the mini upper moiety was located on top of the lower one, with a visualized shallow groove between them. The ureter was dilated with an ectopic orifice or ureterocele. The second was the embedded type (13/83), the feature of which was that mini upper moiety located in the interior top of the lower one within the same capsule. The upper ureter was dilated with an ectopic orifice or ureterocele. The third was the hydronephrosis type (12/83). The severe hydronephrotic upper moiety was almost as big as the lower moiety. The upper ureter was severely dilated and circuitous with an ectopic orifice. The forth was the dual-poor type (2/83). The two moieties were all very small with "Y" shaped ureters and ectopic orifices. The last was the dual-well type (20/83). The upper moiety was almost the same size as the lower one, without apparent dilation of "Y" shaped or double ureters.</p><p><b>CONCLUSION</b>Based on kidney morphology, duplex kidney can be mainly classified into five types which can be depicted by CT urography prior to management and can provide an aid in selecting a successful course of surgical correction.</p>