Classification and clinical significance of the posterior group of renal calyces

To study the anatomical orientation of the posterior group of calyces based on reconstructed images of computerized tomography urography (CTU) and provide a novel classification with its clinical significance. Clinical data of a total of 1321 patients, who underwent CTU examination in our hospital were retrospectively analyzed. Among these, a total of 2642 3-dimensional reconstructed images of CTU scans were considered in this study. Based on the morphology of the renal calyces and the influence on the establishment of surgical access, the posterior group renal calyces are classified into 3 major types including pot-belly type, classically branched and elongated branched. The classically branched type is further classified into 3 sub-types: a, b and c, based on the association of minor calyces of the posterior group to the major calyces. Type a is derived from 1 group of major calyces only, type b is derived from 2 groups of major calyces simultaneously, and type c is derived from 3 groups of major calyces simultaneously. Statistical findings revealed that all kidneys possess posterior group calyces. The percentage of occurrence of pot-belly type, classically branched and elongated branched is 8.06%, 73.13%, and 18.81%, respectively. The anatomical typing of the classical branching type occurred in 19.36%, 68.17%, and 12.47% for types a, b, and c, respectively. In this study, the posterior group calyces were found to be present across all patients. The posterior group calyces were highest in the classical branching type, of which anatomical typing was highest in type b. The typing of the posterior group of calyces could provide an anatomical basis for percutaneous nephrolithotomy (PCNL) puncture from the posterior group.