Yep, and in particular it's not difficult to get sufficient access to circulatory system.

http://my.clevelandclinic.org/health/treatments_and_procedur...

We definitely need more info.

EDIT: Actually, looks like it was in fact an issue of space and blood vessels. From the Google-translation of the Italian article linked elsewhere in the comments:

> The particular malformation of the baby made it impossible for the kidney system donated by the classic conventional technique. The only option then was to use another way of connecting to the bloodstream....In order to create the necessary space for the new kidney, a revolutionary surgical technique which involved the removal of the spleen and the installation of the kidney on splenic vessels of the spleen itself along their course behind the pancreas was applied. The ureter of the transplanted kidney was then implanted directly on the bladder.

https://translate.google.com/translate?sl=auto&tl=en&u=http%...