Renal allograft and ascites
While evaluating a transplanted kidney, we should pay particular attention to the surgical anatomy, presence of ureteral stent, and perinephric collections in addition to ruling out hydronephrosis. Below are examples of peri-nephric hematoma and lymphocele. Note that both these types of collections can be either completely anechoic or demonstrate fibrin strands. Urinomas are mostly anechoic, however.
Below is an example of pelvic ascites around the renal allograft appearing as an anechoic fluid, which should not be confused with the above-mentioned collections. Presence of bowel loops is a clue that it is ascites. Moreover, it would be continuous with fluid in rest of the abdomen. Sometimes, especially on still images, the allograft can be confused with a bowel loop as renal sinus fat mimics bowel gas and parenchyma mimics inflamed bowel wall.