A prominent extrarenal pelvis is an easily identified enlargement of the renal pelvis that is outside the kidney, according to The Free Dictionary by Farlex. This enlargement occurs in approximately 10 percent of the population naturally, reports Radiopaedia.org.
Prominent simply means that it was easy for the medical professional to note and identify the structure, and it is not necessarily indicative of a medical problem. The ureter, or tube that carries urine out of the body, widens to join the kidney and form the renal pelvis, which in turn consists of two or three major calyces that drain the urine into the ureter from the kidney. The renal sinus is the concave section of the kidney, according to InnerBody.