Use of Volume Rendered, Maximum Intensity Projection Images to Assess Whether the Medial Calyx Synonymous with the Posterior Calyx

<b><i>Introduction:</i></b> This paper attempts to verify the anatomical veracity of the belief that in order to enter into a posterior calyx one must aim for the medial calyx during a percutaneous nephrolithotomy (PCNL). <b><i>Methods:</i></b> Volume rendered and maximum intensity projection reconstructions of normal pelvicalyceal systems were assessed in various rotational planes. An experienced urologist decided the appropriate access for PCNL in the upper, interpole and lower calyx on each side. The selected calyx was then viewed on anteroposterior sections to decide whether they were projecting laterally or medially. <b><i>Results:</i></b> Of the 508 calyces studied, the posterior calyx was projecting laterally in 72% and medially in 28%. In the upper calyx, the posterior calyx was projecting laterally in a majority of cases, 94% on the right and 89% on the left. In the right lower calyx, the posterior calyx was pointing laterally in 86%, whereas the distribution on the left was 64%. <b><i>Conclusion:</i></b> Our results refute the belief that the medial calyx is always synonymous with the lateral calyx.