Duplex kidney

Duplex kidney is the most common congenital abnormality of the urinary tract with a reported urographic incidence of around 2% (1)

• presentation is either as an incidental finding or as a cause of recurrent infection. Other presentations include obstruction, stasis and stone
  
  
• the underlying embryological basis can be explained as development of two ureteral buds separately from a single mesonephric duct give rise to a duplex kidney with complete ureteral duplication
  • on the other hand, bifurcation of a single ureteral bud proximal to the ampulla (distal dilated part) gives rise to a duplex kidney with a bifid pelvis or ureter
    
    
• duplex system is explained as the kidney with two pyelocaliceal systems, which may have either single or bifid ureter (partial duplication) or double ureter draining separately into the urinary bladder (complete duplication), with a single renal parenchyma that is drained by two pyelocaliceal systems - duplex ureters are two ureters from one kidney site (could be a bifid ureter (Y shaped ureter) or two separately draining ureters)
  • classifications of duplex kidney are based on its ureter status, which differentiates into two types, complete and incomplete duplex kidney
    • in a complete type duplex kidney, the two ureters empty separately into the bladder, and in a incomplete type, the two ureters are fused to form a single ureteral orifice ('Y' shaped ureter)
      
      
• duplex kidney is an important condition to recognize during childhood because of its frequent association with other urinary tract anomalies, such as ectopic ureteric orifice, vesicoureteric reflux, and ureterocele (2,3)
  • these associations predispose the urinary tract either to recurrent urinary tract infection (UTI) and its complications or to obstruction, both of which may cause long-term renal damage
    
    
• management of duplex kidney mainly depends upon the combinatorial evaluation of kidney size, renal function, and ureter status (e.g. ectopic orifice, ureterocele, and dribbling or not) (4)
  • various surgical procedures exist for the management of duplex kidney, such as hemi- nephrectomy, nephrectomy, ureteral reimplantation, and cyst opening
    • in clinical practice, hemi-nephrectomy is the most commonly used operation (open or laparoscopic technique) for addressing the issues caused by a duplex kidney (5)
    • notably, the upper moiety's status (size and renal function) should be the critical aspect in evaluating the choice of management

Notes:

• duplication of a ureter always affects the renal end of the ureter first and then may extend distally towards the bladder
  • note that the ureter which emerges from the kidney uppermost - or from the uppermost kidney - drains into the bladder lowermost

Reference:

• Privett JT, Jeans WD, Roylance J. The incidence and importance of renal duplication. Clin Radiol 1976; 27: 521-530.
• Hartman GW, Hodson CJ. The duplex kidney and related abnormalities. Clin Radiol 1969; 20: 387-400.
• Bisset 3rd GS, Strife JL. The duplex collecting system in girls with urinary tract infection: prevalence and significance. Am J Roentgenol 1987; 148: 497-500.
• Ma R, Wu RD, Liu W, Wang G, Wang T, Xu ZD, Yu QH, Guo ZY. A new classification of duplex kidney based on kidney morphology and management.Chin Med J (Engl). 2013 Feb;126(4):615-9.
• Zumsteg J, Roberts WW, Wolf JS. Laparoscopic heminephrectomy for benign renal anomalies. J Endourol 2010; 24: 41-47.