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.
Hematoma Lymphocele: thought to be hematoma based on US but drainage revealed clear-appearing lymphocyte-rich fluid.
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.