The "visual dilator system": Initial experimental evaluation of an optical tract dilation technique in percutaneous nephrolithotomy

Background and Purpose: Ascertaining the optimal depth of dilator progression is a crucial factor during tract dilation in percutaneous nephrolithotomy. Dilation is generally guided under fluoroscopy, ultrasonography, or combination of both techniques, and it is still difficult to prevent overdilation causing perforation and vascular injury or underdilation causing difficulty in establishment of access. Thus, improvements in dilation technique bears clinical significance. Our aim was to evaluate the feasibility in an animal model of using the "visual dilator system" for optimal percutaneous tract dilation under real-time visual guidance. Materials and Methods: The visual dilator system consisted of a transparent hollow dilator made of polyvinyl chloride and a rigid ureteroscope inserted within its lumen. The ureteroscope was connected to a standard endoscopic camera system. The dilator system backloaded with an access sheath was passed over a guidewire to dilate the tract and position the access sheath under visual guidance. Saline was used as irrigation to maintain clarity during dilation. The dilation technique was implemented to establish percutaneous access tract in six PCNL simulator models made from fresh porcine kidney placed inside an eviscerated chicken carcass and four female swine (eight kidneys) to experimentally evaluate its feasibility and efficacy. Results: All tracts were successfully established with dilation through the intervening tissue layers, approach into the target calix, as well as access sheath placement being visually monitored through the dilator wall to confirm accuracy. All procedures were free of dilation-related complications such as collecting system perforation, excessive bleeding (in-vivo model), or loss of access. The limited number of animal models and lack of randomized comparative study with other dilator modalities were major drawbacks of the study. Conclusions: The study demonstrates feasibility of precutaneous access tract dilation using a Visual dilator system. This technique can provide visual confirmation of accuracy in dilation to improve safety and efficacy of the procedure.