Figure 44.1
Cross sectional view of the kidney at the interpolar region. Typically, a posterior calyx forms a 30° angle with the vertical axis. This angle should be considered when the needle is inserted. By doing so, the needle is inserted through the respective papilla, and its trajectory is aligned with the infundibulum
Figure 44.2
Computerized tomographic images of the kidney in a patient with hydronephrosis. (a) At the level of the upper pole, the calyx is situated medially. There is no true anterior or posterior major calyx, although some minor calyces may face anteriorly or posteriorly. (b) At the level of the interpolar region, posterior and anterior calyces are clearly distinguishable
Intraoperatively, when a C-arm is used, the best way to identify the posterior calyces of the kidney is by noting their movements on the screen while performing rotational movements of the C-arm. With the patient in the prone position, when the C-arm is rotated towards the surgeon, posterior calyces move medially on the screen while anterior calyces move laterally. On the contrary, when the C-arm is rotated away from the surgeon, the posterior calyces move laterally and the anterior calyces move medially. Again, one should bear in mind that very rarely this rule does not apply, depending on the position of the kidney and the presence of malrotation. The anatomy may be even more confusing in cases of ectopic and anomalous kidneys.
Finally, extreme caution is necessary regarding the neighboring organs especially when only fluoroscopy is used to guide access. At the level of the upper pole, the liver and spleen might cover part of the posterior renal surface on the right and left sides, respectively. As we descend, the liver and spleen move laterally, leaving more space for safe access. The pleura typically descends medially at the level of the origin of the 12th rib and then runs horizontally occupying the medial half of the 11th intercostal space. The lateral half of the 11th intercostal space is usually a safe place to puncture in most, but not all, patients. How can we put these guidelines to good use? When a supra 12th intercostal space access is attempted, the needle should be placed at the lateral half of the 11th intercostal space to minimize the risk of pleural injury but should be kept medially to the posterior axillary line to minimize the risk of liver or splenic injury. Occasionally, a retrorenal colon might be encountered. In one study, a retrorenal position of the colon was observed in 4.7 % in the prone position on abdominal computerized tomography (CT) [5], but is more frequent in patients with advanced age, ectopic and anomalous kidneys and chronic bowel distension (e.g., paraplegic patients) [2]. However, if the surgeon stays medial to the posterior axillary line, a colonic injury is unlikely under normal clinical conditions.
The author strongly recommends the availability of preoperative CT imaging of the abdomen. This exam is valuable not only for evaluating the stone configuration and the stone burden, but also for appreciating the anatomic relation of the kidney to the surrounding organs. Therefore, a better access plan can be devised, which minimizes the risk of liver, splenic and colonic injury.
Placement of a Ureteral Catheter
Placement of a ureteral catheter, cystoscopically, at the outset of the procedure is most helpful. The ureteral catheter is used for contrast medium injection and opacification of the collecting system. Additionally, by injecting contrast, an artificial hydronephrosis is created, which makes subsequent puncture much easier [6]. The author typically uses a 6Fr open end ureteral catheter. A ureteral catheter with an occlusion balloon can also be used, but it is not necessary. Although this is an easy step of the procedure, the ureteral catheter should be inserted carefully. The tip of the catheter is placed at the ureteral orifice. A retrograde study can be performed at this point. Then, a 0.035 in. guidewire is inserted in the ureter, and its tip is coiled at the renal collecting system. The ureteral catheter is then placed over the wire in a railroad fashion under cystoscopic and fluoroscopic guidance. This is the safest way to place the ureteral catheter and avoid injury to or, even worse, perforation of the ureter. The tip of the catheter is placed at the upper calyx to provide extra length. Then, its position can be adjusted after the patient is placed in the final position for percutaneous access.
Injection of Contrast Medium
Injection of contrast allows for opacification of the collecting system. Although this can also be achieved by intravenous injection, direct injection through the ureteral catheter is more versatile and as mentioned before, distends the collecting system. Contrast diluted 50:50 with normal saline should be used. If the contrast is not diluted, the guidewire and the other instruments during access cannot be observed easily on the fluoroscopy images. Contrast should be injected very carefully to avoid excessive pressure, which might cause contrast extravasation outside the collecting system. Should this occur, serious difficulties might be encountered during percutaneous access. For example, the fluoroscopic view will be obscured, and the procedure may need to be abandoned and rescheduled several days later. Rather than using gravity-based systems, the author prefers careful manual injection through a syringe with careful monitoring of the process using the C-arm. Although some surgeons use methylene blue mixed with contrast, the author does not see any significant advantage of this.
Percutaneous Access
The author typically performs PCNL with the patient in the prone position. Therefore, the description of the surgical steps refers to the prone position. Nevertheless, the basic principles of this access technique are also applicable for supine PCNL. The only difference is the movements of the C-arm, which are exactly the opposite of those described for prone PCNL.
- 1.
Identify the posterior calyces. This is most effectively achieved using rotational movements of the C-arm. Typically, when the C-arm image intensifier is rotated towards the surgeon, the posterior calyces move medially on the screen and are observed end-on, while the anterior calyces move laterally. When the C-arm is rotated away from the surgeon, the posterior calyces move laterally and the anterior calyces move medially. If the posterior calyces cannot be identified, injection of a few cc of air is helpful. The air accumulates in the posterior calyces aiding in their identification (Fig. 44.3). Although theoretically there is a small risk of air embolism, this should be considered an extremely rare event, which the author has never witnessed.
Figure 44.3
Distortion of the collecting system anatomy due to a parapelvic cyst. Air has been injected through the ureteral catheter. The air accumulates in the posterior calyces aiding in their identification. The needle has been inserted in a posterior calyx (arrow)
- 2.
Select the appropriate calyx for puncture. This must have been already performed during the preoperative review of the imaging studies, but quite often, the initial plan needs to be changed for several reasons. For example, the initially selected calyx might project above the ribs, necessitating a supracostal puncture. If the surgeon wishes to stay subcostally, obviously another calyx must be selected. Many surgeons prefer to access the kidney through the lower pole only, but this strategy is not ideal for every case.Related posts:
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