Evaluation of non-papillary access on the 3D-printed renal collecting system model in fluoroscopic supine percutaneous nephrolithotomy: a pilot study

Fluoroscopic access techniques may not reliably differentiate between papillary and non-papillary renal access during percutaneous nephrolithotomy (PNL), potentially leading to misinterpretations that could increase complication risks. This pilot study aimed to evaluate whether a novel radiopaque 3D-printed collecting system model could be used to investigate the feasibility of identifying non-papillary accesses using different biplanar fluoroscopic techniques in the supine PNL setting. This experimental study was conducted in February 2023 using a 3D-printed Dentagum resin model of the renal collecting system fixed in a supine position. Five intentionally non-papillary accesses (two lower calyces, three middle calyces) that appeared papillary at a 0° fluoroscopic angle were created. Four biplanar fluoroscopic access techniques (0-30° cephalad, 0-30° caudal, 0-20° lateral, and 0-90°) were then employed to detect whether these accesses could be identified as non-papillary. Among the five non-papillary accesses, 0-30° cephalad detected one (20%), 0-30° caudal detected two (40%), and 0-90° detected two (40%), while 0-20° lateral detected none. Both non-papillary accesses in the lower calyx were correctly identified using 0-90°, with one additionally detected by 0-30° cephalad and the other by 0-30° caudal. Of the three non-papillary middle calyx accesses, only one was detected (via 0-30° caudal), whereas the other two were missed by all tested angles. Additional angles (e.g., 60° lateral-30° cephalad) further increased non-papillary detection rates. This pilot study demonstrates that non-papillary accesses may appear papillary under standard biplanar fluoroscopic techniques, suggesting a risk of misinterpretation and underscoring the potential benefit of incorporating additional imaging angles to improve detection accuracy.