PICA/burden: a staging system for upper tract urinary stones.

A staging system is proposed to stratify upper urinary tract stones by their complexity, location and burden. Burden is defined as the sum of the longest axial diameter of all stones. The kidney is divided into 3 cavities (pelvis, branches or infundibula and calices). The ureter is defined according to 4 segments (upper, middle, lower and juxtavesical). Special descriptors (sand, match heads and fragments) are defined. The use of a scoring diagram allows for a concise description of the complexity and burden of stone in each renal and ureteral cavity. The system facilitates computerized stratification of upper tract stones.