Orthotopic

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A term usually used to describe the position of a transplanted organ or a neo-organ, i.e. another organ surgically modified to serve a different purpose (e.g. an ileal conduit is a closed loop of small bowel that functions as a bladder).

Certain transplanted organs, e.g. the heart and the liver, are generally implanted orthotopically as the various cut ends must be anastomosed to the respective anatomical sites to function correctly. Occasionally, native hearts and livers are left behind and the new transplants placed in a different, but by necessity, nearby anatomical site. This is known as heterotopic transplantation and usually performed when the native organs are thought likely to recover.

By contrast, in kidney transplants, surgical access to the abdomen is easier than access to the retroperitoneum. Furthermore, the vasculature of the kidney is easily anastomosed onto iliac vessels and the long and mobile ureters easily implanted into the bladders via the abdomen. Where the native kidneys remain, these transplants may be described as heterotopic transplant; where the native kidney no longer remain, the transplanted kidney could technically be described as an ectopic kidney, but this term would be confusing as it could be interpreted as congenitally ectopic and it is more common to simply refer to the kidney as being a pelvic transplanted kidney.

Ileal conduits, when functioning as neo-bladders, may be anastomosed to the skin as a urostomy, but can be positioned in the pelvis and anastomosed to the urethra to form a Studor pouch. The latter is regarded as orthotopic as the neo-bladder occupies the same anatomical space as the bladder did previously.

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