Imaging description

Two rules govern the imaging findings of renal duplication with complete ureteral duplication. First, the ureter of the upper renal segment inserts inferiorly and ectopically to the ureter of the lower renal segment (Weigert-Meyer rule) [1], with the upper moiety prone to obstruction and the lower moiety prone to reflux. Second, the appearance of the upper tract predicts the site of insertion, such that a normal pelvicaliceal system and renal segment suggest a normally positioned ureteral orifice, while a hydronephrotic pelvicaliceal system and atrophic renal segment suggest a markedly ectopic ureteral orifice [2]. Accordingly, the diagnosis of complete ureteral duplication is usually radiologically obvious, because the ectopically inserting ureter drains a markedly hydronephrotic moiety (Figure 48.1). However, occasionally the upper pole moiety is small and relatively normal in appearance and then the imaging findings can be subtle and may go unrecognized (Figures 48.2 and 48.3) [3–5]. The term “sub-kidney” has been used to describe the small dysplastic upper moiety of such a duplicated system [6].

Importance

A small subtle upper pole moiety of a duplicated kidney can cause continuous incontinence in girls if there is an associated complete ureteral duplication with an infrasphincteric ectopic ureteral insertion [1–3]. This entity may go unrecognized because the imaging features are relatively inapparent and the ectopic ureter may be invisible even on intravenous urography, presumably due to limited excretion of contrast material from the small dysplastic upper moiety [7]. Correct recognition of the condition allows for relatively straightforward surgical repair, with complete resolution of the distressing symptoms