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having more than 2 kidney is known as -SUPERNUMERARY KIDNEY.
It happens due to splitting of nephrogenic blastema or from seperate metanephric blastemas into which partially or completely reduplicated ureteral stalks enter to form seperated capsulated kidneys.
This condition is very rare and does not require any treatment till unsymptomatic.
Take care

hi welcome to HCM.A supernumerary kidney is an additional kidney to the number usually present in an organism. This often develops as the result of splitting of the nephrogenic blastema, or from separate metanephric blastemas into which partially or completely reduplicated ureteral stalks enter to form separate capsulated kidneys; in some cases the separation of the reduplicated organ is incomplete (fused supernumerary kidney). supernumerary ureter in most fully documented cases of double ureters. Pathologic conditions of the upper urinary tract occurred in more than 50 per cent of the patients with a bifid system, who were prone to have hydronephrosis and calculous disease, and with a double system, who were prone to have complications resulting from supernumerary ureteral ectopia.