Pelvicalyceal System: Endourologic Implications
Anatomic Background
To assist endourologists in making a mental image of the collecting system in three dimensions and learning the exact spatial position of the calices, in 40 cases, before obtaining pelvicalyceal system corrosion endocasts, an iodinated contrast material was injected into the ureter to opacify the collecting system in order to obtain a pyelogram. After radiography, the contrast material was removed and the collecting system was filled with a polyester resin to obtain a three-dimensional endocast. These 40 kidneys enabled a comparative study between the radiographic images and their corresponding three-dimensional endocasts.
Findings and Clinical Implications
The comparative study between pyelograms and three-dimensional endocasts of the collecting system enabled a perception of some remarkable anatomic aspects of the kidney collecting system that are very important to be considered by endourologists during the endourologic procedures.
Presence of Perpendicular Minor Calices
In 11.4% of the cases (16/140 casts) we found a perpendicular minor calyx draining directly into the renal pelvis or into a major calyx ( Fig. 25.1 ). The minor calices perpendicular to the surface of the collecting system, which are seen in the casts, can be superimposed on other structures. Because of this fact, visualization of these calices radiographically can be difficult. Stones in such minor calices can be seen on standard anteroposterior radiographic images as if they were placed in the pelvis or in a major calyx. Thus, one must consider this anatomic detail in cases of stones that do not alter the renal function and that apparently are in the renal pelvis or in a major calyx. In this situation, a complementary radiologic study with lateral and oblique films must be done to determine accurately the position and extent of the stones ( ).
When a stone is located in a perpendicular minor calyx ( Fig. 25.1 ), its removal presents additional difficulties for both extracorporeal shock wave lithotripsy (SWL) and percutaneous nephrolithotripsy (PCNL). Patients with stones in such calices are not good candidates for SWL because these calices invariably present narrow infundibula (smaller than 4 mm in diameter); therefore, the discharge of the disintegrated stone fragments will be difficult ( ). Regarding the percutaneous removal, direct access into the calyx containing the stone is an easy approach; nevertheless, it involves a puncture performed without considering the arterial and venous anatomic relationships to the collecting system. This kind of puncture carries a great risk of injuring a vascular structure ( ). Therefore, in cases of stone in such calices, a variety of safe and refined accesses, techniques, and instruments should be used.
Position of the Calices Relative to the Lateral Kidney Margin
In 39 of 140 casts (27.8%), the anterior calices had a more lateral (peripheral) position than the posterior calices. In 27 casts (19.3%), the posterior calices were in a more lateral position than the anterior calices. Nevertheless, in the majority of the cases (74 casts; 52.9%), the anterior and posterior calices had varied positions: superimposed or alternately distributed (in one region the most lateral were the anterior calices, and in another region the most lateral were the posterior calices).
Since the place of choice to access the collecting system is through a posterior calyx, much effort has been dispensed in an attempt to determine preoperatively which calices are anterior and which calices are posterior. Previous studies have presented contradictory results and have led to misunderstanding of this subject ( ). Because we described a kind of kidney collecting system, found in the majority of endocasts, on which the calices are disposed in varied positions (superimposed or alternately distributed), we may affirm that the position of the calices cannot be defined as more lateral or more medial. Considering the large variation of the calices (more than 50% in varied positions), we believe that precise determination of calyceal position becomes difficult with the common radiologic methods, even using oblique and lateral views ( ). To solve this problem quickly and inexpensively, during endourologic procedures, with the patient in the prone position, injection of room air into the collecting system will rise to the more posterior portions of the collecting system, determining which calices are placed posteriorly (radiolucent contrast) ( ; ).
Position of the Calices Relative to the Polar Regions and to the Kidney Mid-Zone
The superior pole was drained by a midline calyceal infundibulum in 98.6% of the cases. The midzone (hilar) was drained by paired calices that were arranged in two rows (anterior and posterior) in 95.7% of the cases. The inferior pole was drained by paired calices arranged in two rows in 81 casts (57.9%) ( Fig. 25.2A ) and by a single midline calyceal infundibulum in 59 casts (42.1%) ( Fig. 25.2B ).
Concerning the calyceal drainage of the kidney polar regions, many investigators affirmed that there usually is only one calyceal infundibulum draining each pole ( ; ). In our study, the superior pole was drained by only one midline calyceal infundibulum in 98.6% of the cases. However, the inferior pole was drained by paired calices arranged in two rows in 81 of 140 cases (57.9%) and by one midline calyceal infundibulum in 59 cases (42.1%). These results are important to endourology; it will be easier to access endoscopically a polar region drained by a single infundibulum, which usually has suitable diameter, rather than a polar region drained by paired calices ( Fig. 25.2 ). Because the inferior pole is drained by paired calices in 57.9% of the cases, one must keep in mind this anatomic detail, both to plan and perform the intrarenal access and the endoscopic procedures in the inferior pole. The calyceal drainage of superior and inferior poles is also of utmost importance in SWL and was fully discussed in previous papers ( ). Concerning the kidney midzone (hilar) drainage, our results show that this region is drained by paired calices arranged in two rows (anterior and posterior) in 95.7% of the cases ( Fig. 25.2 ). These results should also be retained by endourologists to access and work in the midkidney.
Anatomic Relationships of Intrarenal Vessels (Arteries and Veins) With the Kidney Collecting System
Relevance for the Intrarenal Access by Puncture
Percutaneous procedures are relatively invasive, and complications may occur. One of the most significant complications is vascular injury that occurs when the urologist is obtaining intrarenal access. This problem may have several cumbersome consequences, including intraoperative hemorrhage, hypotension, loss of functioning renal parenchyma, arteriovenous fistula, and pseudoaneurysm ( ; ; ; ).
The goal of this item is to offer an anatomic depiction of refined details concerning intrarenal vessels and their relationships to the collecting system, showing how to perform safe percutaneous intrarenal access by keeping as many renal vessels as possible intact during puncture.
Material Studied for the Anatomic Background
We analyzed 62 retrograde pyelograms and the corresponding three-dimensional polyester resin corrosion endocasts of the kidney collecting system together with the intrarenal arteries and veins, obtained from fresh cadavers.
The kidneys were punctured under fluoroscopic guidance and the endocasts obtained with the needles positioned in the place of puncture ( Fig. 25.3 ). For comparative analysis, we studied kidneys that had been punctured through a calyceal infundibulum and kidneys punctured through a calyceal fornix.
Intrarenal Access Through an Infundibulum
Superior Pole.
Puncture is most dangerous through the upper pole infundibulum because this region is surrounded almost completely by large vessels ( Fig. 25.4 ). Infundibular arteries and veins course parallel to the anterior and posterior aspects of the upper pole infundibulum. In our series, injury to an interlobar (infundibular) vessel was a common consequence of puncturing the upper-pole infundibulum (67% of kidneys) ( Fig. 25.5 ); the injured vessel was an artery in 26% of those cases.
The most serious vascular accident in upper infundibulum puncture is a lesion of the posterior segmental artery (retropelvic artery). This event may occur because this artery crossed and is related to the posterior surface of the upper infundibulum in 57% of the cases ( Fig. 25.6A ) ( ). Fig. 25.6 (B and C) shows an upper infundibulum puncture in which the needle tract produced complete laceration of the posterior segmental artery. Because the posterior segmental artery (retropelvic artery) may supply up to 50% of the renal parenchyma, injury to it may result in significant loss of functioning renal tissue, in addition to causing hemorrhage ( ).
