[MRI evaluation of a supernumerary kidney fused with a horseshoe kidney].

We present the case of a patient in whom a horseshoe kidney was discovered during US examination performed for abdominal pain. MRI confirmed this finding and also revealed a supernumerary kidney. The three kidneys were fused, with the supernumerary kidney forming the isthmus of the horseshoe kidney. Whereas horseshoe kidney is a relatively common renal malformation, a supernumerary kidney is one of the rarest renal malformations. The coexistence of these two malformations and especially the particular disposition of the supernumerary kidney is very rare. Knowledge of this malformation is interesting because it can lead to complications such as lithiasis, hydronephrosis, infections, and neoplasms and because it has important implications for surgical planning.