Puncture along the axis of the targeted renal calyx is based on the same principle used to establish a percutaneous renal passage during percutaneous nephrolithotomy, which is derived from the anatomical structure of the kidney and blood vessels.3 Cone-like pyramidal structures are found in the medulla of the kidney. The bottom of the pyramid is toward the cortex, and the tip of the pyramid forms the papilla. which inserts into the bottom of the conical calyx. The renal segmental artery and interlobar artery are shaped around the renal calyx and renal vertebrae. The axis passing through the targeted renal calyx also passes through the axis of the adjacent renal pyramidal body, which is the optimal anatomical route with less vascular distribution.6 Meanwhile, the maximum angle and operating range of renal enzoscopy can be reached throughout the puncture route in the axis of the renal calyx.6
In clinical practice, ensuring that the percutaneous renal puncture is routed precisely through the axis of the targeted renal calyx is difficult.7 It requires an accurate location of the central axis of the 3D conical renal calyx and precise, simultaneous navigation in three dimensions (X, Y, Z). At present, the commonly used 2D guidance methods (i.e., plain radiography, B-US) cannot accurately locate the skin puncture point or route,8–10 which is the most significant technical obstruction to using percutaneous renal puncture.
The radiography-guided puncture route and the axis of the targeted renal calyx are always in the same longitudinal plane, although these two lines cannot be guaranteed to overlap in this plane. It often takes multiple puncture points, multiple angles, and repeated attempts to penetrate the targeted renal calyx, and it often deviates from the axis of the targeted renal calyx, resulting in injury and bleeding of the blood vessels around the renal vertebrae and renal calyx, which limits the scope of nephroscopy and affects the efficiency of stone removal.
Although US guidance can show the targeted renal calyx at multiple angles and monitor the puncture needle through the center line of the 2D section of the targeted renal calyx,7 it is difficult to determine whether the 2D section selected by US contains the axis of the targeted renal calyx, which is also the geometric axial section of the pyramidal targeted renal calyx. Especially for a targeted renal calyx with hydronephrosis, which deforms into an oval body or sphere, it is even more difficult to locate the axial section of the targeted renal calyx using US. Thus, it could be concluded that, with US guidance, it is often impossible to pass the axis of the targeted renal calyx accurately, resulting in injury to, and bleeding from, the blood vessels around the renal vertebrae and renal calyx, as well as allowing only limited intraoperative nephroscopic movement.
Accurate target percutaneous renal calyx longitudinal puncture has always been the biggest challenge in percutaneous renal surgery. In recent years, a variety of percutaneous renal puncture navigation systems have emerged, including electromagnetic positioning navigation11 and iPad augmented reality navigation12 and so on. The above techniques can achieve fast and safe puncture in the operation to some extent, but their disadvantages are also significant. IPad augmented reality auxiliary system needs complex equipment, software and professional personnel. In addition, due to the movement of renal position caused by respiratory activity during the operation, there is a certain deviation between the augmented reality image and the actual position of the patient, while the iPad augmented reality auxiliary system does not have real-time position tracking of the puncture needle, which may cause the puncture needle to deviate from the target puncture line. Electromagnetic positioning and navigation technology also requires complex electromagnetic equipment and professionals, and the flexible ureteroscope needs to be placed into the target renal calyx in advance. Ureteral stricture and kidney stone obstruction will limit its use. In addition, because there is no real-time monitoring, it is difficult to ensure that the adjacent organs of kidney are not damaged during the puncture. The above shortcomings limit the clinical application of these techniques, resulting in their exploratory application in only a small number of patients.
The fusion of virtual 3D images and real-time ultrasound images may be the development direction of percutaneous renal puncture navigation in the future. Based on the above assumption, we designed 3D visualization technology combined with real-time ultrasonic monitoring to navigate percutaneous renal puncture more precisely via three standardized steps for the first time. First, we calculated and marked the geometric axis of the targeted renal calyx and then marked the optimal puncture point on the skin using the grid surface patch. Second, we measured and segmented the optimal simulated guided section image and matched the tangent precisely on the skin using the grid location patch. This tangent line is the optimal placement position of the US probe on skin. Third, we moved the US probe around the puncture point and along the localization tangent. By fusing and comparing the observed sections of the collecting system with the optimal simulated guiding cut section segmented using 3D visualization technology, we determined the optimal direction of the US probe. Throughout these steps, the navigational information gained by 3D visualization technology is fused with real-time guidance of B-US, thereby successfully taking advantage of the rapid, stereoscopic, accurate percutaneous renal puncture navigation.
In this study, because we accurately combine the positioning function of 3D visual image with the real-time ultrasonic monitoring function, we overcome the shortcomings of 3D image and ultrasonic localization, and realize the accurate location of skin puncture point and the accurate guidance of puncture path. First of all, the postoperative puncture channel is highly in line with the longitudinal axis of the target renal calyx, which meets the requirements of accurate percutaneous renal puncture. Secondly, on the basis of accurate puncture, compared with the standard B-U-guided puncture, the loss of hemoglobin, postoperative blood transfusion rate and interventional embolization rate in the 3D visualization navigation puncture group decreased significantly, and the stone clearance rate increased to 90.48%. In addition, although the steps of 3D visual navigation puncture are complex, it does not take a long time for each patient after skilled operation, and most of the work is completed before the operation, which greatly shortens the puncture time and operation time. Also, this technology only needs simple software operation learning, and does not need complex equipment. It is very easy to popularize and apply.