The spleen is a lymphatic organ (full of white blood cells), the kidney is a mechanical filter coupled with molecular transport to pick back the good stuff and

The spleen is a lymphatic organ (full of white blood cells), the kidney is a mechanical filter coupled with molecular transport to pick back the good stuff and the water from the filtrated serum. Beside being solid organs with a roundish shape, they have nothing in common. Kidneys are usually grafted in the pelvis, using IIRC the iliac vessels, because it is more convenient and allows to keep the existing kidneys that may have some residual function. Maybe that kid had malformed iliac vessels as well...