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PERCUTANEOUS NEPHROLITHOTOMY

PERCUTANEOUS NEPHROLITHOTOMY

Percutaneous nephrolithotomy (PCNL) is a minimally invasive procedure for the treatment of kidney stones. In this procedure, a surgical access tract is established between the skin and the renal collecting system. The tract is typically created under fluoroscopic guidance, with needle puncture followed by tract dilation.

Although more invasive than extracorporeal shock wave lithotripsy (ESWL, see Plate 10-12) and ureteroscopic laser lithotripsy (URSLL, see Plate 10-34), PCNL is highly effective for large kidney stones and patients with more complex stone disease. Before the introduction of PCNL, these challenging patients were managed almost exclusively with open or laparoscopic surgery, which is far more invasive, requires longer convalescence, and has higher rates of morbidity, mortality, and stone recurrence. In contemporary practice, however, open surgery is now performed only in special situations, such as morbid obesity, numerous stenotic infundibulae, ectopic kidneys without safe percutaneous access, extremely complex stones that would require numerous access tracts, and coagulopathies.

 

PERCUTANEOUS NEPHROLITHOTOMY: CREATION OF ACCESS TRACT
Plate 10-13
PERCUTANEOUS NEPHROLITHOTOMY: CREATION OF ACCESS TRACT

INDICATIONS

The factors that determine the difficulty, and thus appropriateness, of PCNL include the degree of hydronephrosis, total stone burden (i.e., surface area), stone composition, number of calyces involved, presence or absence of infundibular stenosis, and presence or absence of anatomic abnormalities (e.g., horseshoe and pelvic kidneys).

The presence of hydronephrosis makes it easier to maneuver rigid instruments within the collecting system, and therefore PCNL is preferred over other techniques in patients with hydronephrotic kidneys.

A large stone burden is a common indication for PCNL because large fragments can easily be extracted via single or multiple percutaneous tracts. In contrast, ESWL requires patients to pass these fragments spontaneously, and URSLL requires removal of these stones through the ureter.

Stone composition is an important factor because hard stones, such as those composed of cystine or calcium oxalate monohydrate, often do not respond to ESWL and are more difficult to fragment with URSLL. Thus PCNL is usually preferable.

The more calyces that contain stones, the lower the success rate of ESWL and URSLL, since it is difficult to treat stones in multiple locations with these modalities.Thus PCNL is preferred because of its higher stone-free rate and reduced need for ancillary procedures.

Unusual collecting system anatomy, in particular infundibular stenosis, often precludes successful elimination of stone fragments following ESWL and URSLL, again making PCNL the better choice.

Finally, congenitally abnormal kidneys, such as horseshoe kidneys and pelvic kidneys, usually have anteriorly located ureteropelvic junctions, which can make spontaneous passage of stones after ESWL and ureteral extraction of stones during URSLL very challenging. The unusual position of the ureteropelvic junction, along with the collecting system dilation that often accompanies these ectopic kidneys, makes PCNL the preferred choice.

 

TECHNIQUE

Patients scheduled for PCNL must have a documented sterile urine culture because PCNL in the setting of urinary tract infection can lead to urosepsis. The procedure is performed under general anesthesia, and the patient is typically prone. More recently, however, techniques have been described in which PCNL is performed in the supine and flank positions.

Imaging is typically performed using fluoroscopy. Before access is attempted, most surgeons deploy a ureteral catheter into the ipsilateral ureter for retrograde injection of contrast or irrigant, which facilitates visualization of the renal collecting system.

The key to successful PCNL is the site chosen for entry into the collecting system. Lower pole access is excellent for stones that are in the lower pole or renal pelvis, but it offers limited access to the other calyces and is thus not well suited for staghorn stones, complex stones, or stones in multiple calyces. Lower pole access, however, is associated with a smaller risk of entering the pleural space. In contrast, upper pole access provides the surgeon the best access to the entire collecting system, but it is associated with a modest risk of entering the pleural space.

In most situations, a posterior calyx should be chosen for access because its orientation permits entry into the renal pelvis and other calyces from a typical posterolateral approach. If the patient has a solitary stone, however, it generally makes most sense to enter the calyx that contains the stone, even if it is in an anterior position.

Generally, the posterior upper pole calyx permits maximum stone extraction from a single access tract.

NEPHROSCOPE AND SONOTRODE
Plate 10-14
NEPHROSCOPE AND SONOTRODE


Once a calyx has been selected, an important decision must then be made between intercostal or subcostal placement of the access tract. Subcostal tracts are preferable because they minimize the chance of pleural injury, which could result in pneumothorax, hemothorax, or hydrothorax. Such tracts, however, may place a significant amount of torque on the kidney, potentially causing damage.

In general, the fear of intercostal tracts is unfounded as long as care is taken to assure that the sheath remains inside the collecting system. Under these conditions, most small pleural transgressions will not result in complications. In contrast, a pleural transgression that is associated with a sheath outside of the collecting system can result in the passage of irrigant, air, or blood into the pleural space. A postprocedure chest radiograph or chest fluoroscopy is recommended to permit early diagnosis of pulmonary complications, so that a chest tube can be placed if necessary.

Once the access site has been selected, the procedure is initiated with the percutaneous deployment of a needle into the kidney. Contrast material is injected through the needle to confirm appropriate positioning, and a wire can then be placed into the kidney through the needle. Using this wire, a tract is developed between the skin and the collecting system.

In the past, tract dilation was accomplished using either metallic telescoping dilators (the Alken system) or Teflon-coated graduated dilators (the Amplatz system). At present, however, most centers use balloon- dilating systems. These offer single-step dilation that causes less bleeding than previous systems because of the application of radial, rather than shear, force. In balloon dilation, a deflated balloon with a hollow core is passed over the previously deployed wire. The balloon contains radiopaque markers at its proximal and distal edges to ensure proper positioning. The balloon is then inflated under pressure. Once the balloon is turgid, a plastic sheath can be deployed over the balloon. The balloon is then deflated and removed, while leaving the sheath in position for continued renal access.

 Balloon dilators, however, are not always successful. In some collecting systems, the balloon may not reach the target because of the lead length problem; specifically, the tip of the balloon-dilating catheter may hit the stone or be within a small calyx, but the body of the balloon may not reach the collecting system. In addition, patients with a history of prior renal surgery may have a perirenal scar that prevents full balloon inflation, leading to a “waist” in the tract. Finally some obese patients may have so much subcutaneous fat that the balloon is not long enough to reach the collecting system.

Multiple access tracts may be required in patients with large or complex stones, such as staghorn calculi, or with duplicated collecting systems. In some cases, the need for multiple access tracts can be obviated using the stone push technique, in which a trocar needle is placed directly onto a stone located in an inaccessible calyx. The needle is then used to push the stone into the renal pelvis, from which it can be more easily extracted.

Once access into the collecting system has been established, the stones are removed. As most access tracts are 30 Fr in diameter (10 mm), stones up to 10 mm can be directly grasped and extracted using a flexible nephroscope. Larger stones require fragmentation (lithotripsy), which can be accomplished using several different devices. The most common remains percutaneous ultrasonic lithotripsy, in which a probe with a vibrating tip (known as a sonotrode) produces ultrasonic energy that fragments the stones. Because the probe is hollow, it can be attached to suction, such that stone fragments are extracted as they are created. Pneumatic lithotripsy (hammer-like effect) has also been used for stone fragmentation alone or in conjunction with ultrasonic stone ablation. More recently, some authors have described the use of a holmium laser to fragment stones. Each of these modalities can effectively ablate stones of any composition; however, ultrasonic lithotripsy remains the gold standard.

After all stones have been extracted, the kidney is drained to facilitate healing. A nephrostomy tube can be deployed, but a more recent development is the “tubeless PCNL,” in which an indwelling ureteral stent is deployed and no percutaneous tract is left. Although not truly “tubeless,” these stents do not appear to have higher bleeding rates than conventional nephrostomy drains, even despite the lack of a large tube to tamponade the access tract.

 

ULTRASONIC LITHOTRIPSY OF LARGE STONES
Plate 10-15
ULTRASONIC LITHOTRIPSY OF LARGE STONES

COMPLICATIONS

The major complications associated with PCNL are hemorrhagic. Occasionally, PCNL procedures need to be aborted before complete stone ablation if bleeding prohibits adequate stone visualization. Bleeding is most commonly venous in origin, and it can be controlled by inflation of the balloon to achieve a tamponade effect. Bright red blood is a sign of arterial bleeding and should be treated with immediate tamponade followed by intravascular embolization as needed.

Another complication of PCNL is perforation of the renal collecting system, which can result in ascites. In severe cases, the intraperitoneal fluid can inhibit diaphragmatic contraction and may necessitate prolonged intubation.

Finally, residual stones are common after PCNL procedures. Some surgeons perform a “second look” procedure 1 to 2 days after the primary procedure using the same access tract. Smaller residual fragments can be treated with active surveillance, ESWL, or ureteroscopy.