Percutaneous Endourology

Percutaneous surgery is based on needle and guidewire access to the kidney and the upper urinary tract. Once guidewire access is obtained, various catheters can then be placed into the kidney, either for drainage or for facilitation of antegrade intrarenal or ureteral endoscopic procedures. The tract must first be established and should provide a straightforward route to the kidney, allowing bloodless instrumentation. If more than renal drainage is desired, endoscopic surgery can then continue as a single or staged procedure. With recent advances, many invasive open urologic procedures are now performed endoscopically through small-diameter percutaneous access tracts.

The first percutaneous nephrostomy description of record was published in 1865 by Thomas Hillier, MD. Dr. Hillier, a young physician in London, repeatedly drained a 4-year-old boy's kidney, which he believed at that time to be congenitally obstructed. He performed multiple nephrostomies from 1863-1868 in an attempt to relieve the patient's abdominal distention, hoping to create a permanent fistula to the skin. This child ultimately died 5 years later, after persistent tapping, due to severe abdominal distention that led to ambulation and health complications. He was found to have a severely hydronephrotic kidney, as shown below, upon pathologic review. None of Hillier's contemporaries followed his example, and percutaneous renal procedures received no further attention until the mid 1950s.

See the image below.

Goodwin and associates provided the next description of percutaneous renal access in 1955.[1] They reported their experience with therapeutic percutaneous nephrostomies in 16 patients. In 1976, Fernstrom and Johansson described a procedure in which a renal pelvic calculus could be extracted through a percutaneous tract.[2]

Later, Blandy and Singh (1976) published important data, affirming that aggressive surgical management was necessary when treating staghorn calculus disease. They reported a high 10-year mortality rate (28%) with conservative treatment, compared with a 10-year mortality rate of 7.2% following surgical removal of the stone. In 2005, the clinical practice guideline report for the management of staghorn calculi by the American Urological Association guidelines panel confirmed that percutaneous treatment of staghorn calculi should be first-line treatment for most patients.[3]

The technology and techniques involved in percutaneous renal access and percutaneous surgery have evolved rapidly over the last 30 years. Percutaneous procedures are now performed on a routine basis for both diagnostic and therapeutic procedures. The modality of percutaneous surgery is evolving continuously as the endoscopes, radiography, and complementary instruments continue to improve.

Percutaneous access to the renal collecting system may be performed for diagnostic procedures or for establishing a tract through which therapeutic interventions and endoscopy are performed.

Diagnostic indications

Antegrade pyelography refers to the administration of radiopaque contrast material into the kidney and collecting system via a percutaneously placed needle or catheter system. It is rarely performed alone because of the current availability of other less-invasive radiographic techniques (eg, intravenous urography, ultrasonography, magnetic resonance imaging, computed tomography, retrograde studies) but is a common step toward other more complex endoscopic interventions. During most percutaneous-access procedures to the kidney, routine antegrade pyelography is performed. This often provides important information about the intrarenal collecting system architecture and can help plan subsequent therapeutic interventions.

Pressure/perfusion study (Whitaker test) is similar to an antegrade nephrostography but adds an in-line manometer to measure intrarenal collecting system pressures while filling and emptying. This test has largely been replaced by noninvasive nuclear medicine examinations of the kidney (eg, diuretic renography or scintigraphy [renal scan]).

However, in cases in which the diuretic renal scan findings are equivocal, a Whitaker test may be performed. During this test, dilute contrast is instilled at a rate of 10 mL/min via a percutaneously placed needle or small nephrostomy tube in the renal collecting system. The collecting system architecture is reviewed as the upper urinary tract is filled and drained of contrast. A urethral catheter allows drainage of the bladder and measurements of bladder pressures. With the kidney being perfused in an antegrade fashion at a flow rate of 10 mL/min, differential pressures between the renal pelvis and bladder of less than 13 cm of water are normal (not obstructed), 14-22 cm of water suggest mild obstruction, and more than 22 cm of water suggests moderate-to-severe ureteral obstruction.

Therapeutic indications

Most of the following therapeutic interventions were once performed via an open approach. With percutaneous renal access, these interventions carry significantly decreased morbidity than they did with open surgery. Percutaneous renal access is a minimally invasive technique that allows the patient quicker recovery time, better cosmetic effect, and a shorter hospital stay.

Nephrostomy catheter drainage

When retrograde drainage of the kidney is not indicated, is technically difficult (eg, impacted stone, tumor, stricture), or is not advisable (eg, ureteral obstruction, sepsis) and when drainage of the kidney is paramount, the kidneys are drained percutaneously. This is performed with either ultrasonography or fluoroscopic localization of the collecting system. In this setting, the surgeon's goal is to obtain drainage, not to perform other more complex therapeutic maneuvers. Small-diameter 8-12F catheters are placed over the access guidewire to obtain drainage of the upper urinary tract. This allows preservation of renal function, relief of symptoms, and effective and rapid drainage of purulent material from an obstructed kidney.

Antegrade ureteral stenting

A ureteral stent is a catheter that is placed into the ureter to facilitate internal drainage of the upper urinary tract. Most commonly, it is placed cystoscopically through the bladder. When retrograde stenting of the ureter is unsuccessful, the antegrade percutaneous approach is used. In this setting, percutaneous guidewire access is obtained first. Then, the guidewire and catheter are directed down the ureter and into the bladder fluoroscopically. If stenting is not possible cystoscopically due to ureteral tortuosity, false passages, or the inability to identify the orifice endoscopically, then the antegrade approach is frequently successful.

Treatment of ureteral strictures

Ureteral strictures are treated with balloon dilation and/or endoscopic incision. Endoscopic incisions are performed with endoscopes placed transurethrally/ureteroscopically or through a percutaneous renal access tract. Strictures are caused by iatrogenic injuries, gynecologic diseases such as pelvic endometriosis, or prior urinary tract surgeries. Dilation therapy alone for ureteral strictures has the lowest overall treatment success rate (30%), while endoscopic incisions produce better results. However, results can vary based on the length of the strictured segment, the extent of periureteral and retroperitoneal fibrosis, and a history of radiation therapy.

Percutaneous endopyelotomy

Similar to ureteral strictures, this refers to the endoscopic treatment of an obstructed ureteropelvic junction (UPJ).[4] This disorder is either primary (ie, congenital) or secondary (ie, due to chronic irritation from stone disease). Incision of the UPJ can be performed ureteroscopically or via a percutaneous access tract. Success rates are similar in both groups, but percutaneous treatment is particularly useful in complex cases in which associated intrarenal calculi are present, as ahown below. The percutaneous removal of these stones is essential when planning endopyelotomy because stone fragments that remain can migrate into the incision and be associated with a granulomatous reaction and subsequent obstruction. Antegrade endopyelotomy success rates range from 72-87% with up to 3 years of follow-up.

See the image below.

Various minimally invasive procedures have recently emerged for the treatment of UPJ obstruction. These include laparoscopic pyeloplasty and percutaneous endopyeloplasty. However, in appropriately selected patients, percutaneous endopyelotomy remains an appropriate and effective treatment option. Studies suggest that the success rate of endopyelotomy is decreased when a crossing vessel is the primary cause of UPJ obstruction, when the renal function is poor, or when severe hydronephrosis or a long segment (>2 cm) of ureteral obstruction is present. In these situations, open or laparoscopic pyeloplasty may be more appropriate.

When percutaneous endopyelotomy is performed, access to the kidney is established and a guidewire is passed across the UPJ. A full-thickness incision is then made via the UPJ with a cold-knife, electrocautery, or laser. An indwelling ureteral stent is placed for 3-5 weeks, and a nephrostomy tube is often left for 24-48 hours postoperatively.

Percutaneous endopyeloplasty

Endopyeloplasty has emerged as a viable option that combines antegrade endopyelotomy with endoscopic suturing, like that used with laparoscopic pyeloplasty. Some centers are now using endopyeloplasty.

Percutaneous endopyeloplasty, as described by Gill et al[5] (2002) and Desai et al[6] (2004), consists of retrograde ureteral catheterization, percutaneous renal access, longitudinal endopyelotomy incision using a cone-tip Bugbee electrode and cutting current, mobilization of the distal ureter, percutaneous horizontal suturing vertically of the endopyelotomy incision, and then antegrade placement of a double-J ureteral stent and nephrostomy tube. Suturing was performed using a modified 5-mm laparoscopic suturing device (SewRight SR5, LSI Solutions, Victor, NY) inserted through the working channel of the nephroscope.

Although results show percutaneous endopyeloplasty is technically feasible and safe, this procedure carries significant limitations. Relative contraindications include long-segment stenosis, extrinsic crossing vessels, and prior surgery for UPJ obstruction. In addition, long-term data and additional studies from multicenter institutions with larger patient groups and longer follow-up are necessary to make percutaneous endopyeloplasty a first-line treatment option for primary UPJ obstruction.

Percutaneous nephrolithotomy

Certain upper urinary tract stones that are not amenable to other modalities of treatment (eg, shockwave lithotripsy, retrograde ureteroscopic treatment) are frequently treated via this percutaneous endoscopic approach.[7] Commonly, infected stone burdens are treated percutaneously because this facilitates not only stone fragmentation but also prompt evacuation of the infected material. Often, initial percutaneous drainage of an infected system with a stone is needed, allowing for a cooling-down period prior to definitive therapeutic interventions. Large stones (>2.5 cm in diameter), including staghorn calculi, should be treated via percutaneous endoscopic surgery. Open surgery is performed only for a small minority of staghorn calculi that would require an excessive number of percutaneous access tracts to clear the entire stone burden.

Another indication for percutaneous nephrolithotomy (PCNL) is symptomatic calculi located in a caliceal diverticulum (dilated cavities connected to the collecting system by a narrow infundibulum). In this situation, percutaneous treatment results in 88-100% stone-free rates and symptom-free rates. Large stone burdens or those within a long-necked diverticulum are best treated in this fashion.

Traditionally, PCNL has been performed in the prone position and is an established technique with a high success rate a low morbidity.[8] However, the prone position can be challenging and is associated with high risk in morbidly obese patients with cardiopulmonary disease; thus, the supine position has been established to help overcome these drawbacks. Theoretical advantages of the supine position include safer and easier positioning for the patient, less cardiovascular change and risk, no need for patient reposition, and possible shorter operating time.

Theoretical disadvantages of the supine position include anterior/lateral puncture sites, potentially increasing the risk for visceral organ injury (eg, colon, liver, spleen); collapse of the collecting system; and difficulty with approaching the upper pole calyx.[9]

Liu et al preformed a systematic review and meta-analysis of percutaneous nephrolithotomy for patients in the supine versus prone position and found that PCNL in the supine position was as safe and efficacious as the conventional prone position; however, no overwhelming evidence suggested one position was better then the other.[10]

Although supine PCNL has become a option for the removal of large stone burdens, additional prospective, randomized controlled studies are needed to assess the safety and long term efficacy of this approach. Surgeon preference and experience should ultimately guide the choice of patient positioning during PCNL.

Miniature percutaneous nephrolithotomy (Mini-Perc)

Miniature percutaneous nephrolithotomy (Mini-Perc) was originally described by Helal et al as a means of extracting renal stones refractory to ESWL in a 2-year old premature child. The method described by Helal et al involved dilating sequentially to a 16F sheath followed by use of a 12F vascular peel-away sheath. A pediatric endoscope was used to extract stones.[11] Jackman et al modified the Mini-Perc technique to use an 11F ureteral access sheath. In their series of 9 cases, the stone-free rate was 89% at a follow-up of 3.8 weeks.[12]

Proponents of the Mini-Perc procedure cite limited blood loss, increased maneuverability, decreased postoperative pain, and a limited hospital stay. Limitations of the procedure include having to fragment stones into small enough pieces to fit through a reduced-sized sheath and longer operative times.[13]

Mishra et al recently conducted a prospective study comparing Mini-Perc with standard PCNL for stones 1-2 cm in size.[14] The Mini-Perc group used an 18F sheath (range 15-20F) compared with a 26.8F sheath (range 24-30F) in the standard PCNL group. The study concluded that the Mini-Perc technique had longer operative times (45 vs 31 min), lower blood loss (0.8 vs 1.3 g hemoglobin), and a shorter hospital stay (3.2 vs 4.8 d). The postoperative stone-free rates were similar between the 2 groups at a follow-up of 1 month.

Additionally, Cheng et al conducted a randomized trial comparing Mini-Perc to standard PCNL. They concluded that the Mini-Perc was associated with longer operative times (134 vs 89 min) secondary to a smaller sheath; however, blood loss necessitating transfusion was statistically significantly lower (1.4% vs 10.4%). Stone-free rates for staghorn and simple renal pelvic stones were similar between the 2 groups; however, the Mini-Perc group had a statistically significantly higher stone-free rate with multiple calyceal stones. Hospital stay, postoperative pain, and stone clearance rates were similar in the 2 groups.[15]

Tubeless percutaneous nephrolithotomy

Tubeless PCNL refers to the technique of performing a nephroscopic procedure via a fresh access track without subsequent placement of a nephrostomy tube.

Earlier techniques used an internal ureteral stent for drainage[16] ; however, more recent studies have focused on totally tubeless drainage in which neither an external nephrostomy nor an internal ureteral stent are left after the procedure.[17] Benefits of the tubeless and totally tubeless techniques include reduction in postoperative pain and a shorter hospital course.[18, 19] Modifications of the totally tubeless technique are the use of hemostatic agents such as fibrin glue injections to help seal the nephrostomy tract following PCNL.[20] Wang et al performed a meta-analysis of 7 studies and concluded that tubeless PCNL offers the advantage of reduced hospital stay and need for postoperative analgesia in select, uncomplicated cases. There were no differences in operation duration or hematocrit change between the 2 groups.[21]

Although tubeless PCNL has been shown to be feasible and to reduce postoperative pain, it is contraindicated in complicated cases (eg, bleeding, renal perforation, extravasation, infection) or if a staged PCNL is necessary. Additional studies are needed to demonstrate the clear clinical benefit of tubeless PCNL.

Perfusion chemolysis to dissolve and clear certain renal stones

This therapy is now largely adjunctive in nature owing to the advent of new lithotripsy techniques and oral chemolytic agents (eg, potassium citrate). Chemolysis of uric acid and cystine stones is particularly effective. Bicarbonate solution produces adequate alkalinization to dissolve uric acid debris while a combination of tris- (hydroxymethylene)-aminomethane (THAM) and Mucomyst (N -acetylcysteine) is used for cystine stones. Following nephrolithotomy, percutaneous catheters are left in the collecting system and used to instill and drain irrigant that is used to dissolve and flush residual fragments.

To limit risks, a double-catheter system should be used. This enables simultaneous instillation and drainage. A combination of catheters should be used. One may use 2 separately placed nephrostomy catheters or a ureteral catheter in conjunction with a nephrostomy tube. The irrigation catheter should be placed close to the stone to ensure adequate exposure of the stone to the irrigant. One should not use perfusion therapy in the presence of infected urine because this may result in sepsis. A flow rate of 100-120 mL/h is standard. An in-line manometer is useful for measuring and maintaining low (< 20 cm of water) intrarenal pressures. This is particularly useful when irrigants such as Renacidin are used to dissolve infectious matrix debris. The time necessary for stone dissolution depends on the stone burden and composition. Irrigations may dissolve in a few days (ie, with uric acid) or may require weeks (ie, with cystine or struvite). As a rule, 1 cm per month can be expected.

The irrigants that may be used include potassium or sodium bicarbonate for uric acid stones; D-penicillamine, N -acetylcysteine, or tromethamine-E solution for cystine stones; or Suby solution (G or M) or hemiacidrin (Renacidin) for struvite or apatite stones.

Renacidin irrigant is used specifically for infectious matrix stone burdens and can be useful in clearing residual debris after PCNL. Care must be taken when using this irrigant because high intrarenal pressures may cause inadvertent vascular absorption with subsequent hypermagnesemia. An in-line manometer and careful attention to maintaining low intrarenal pressures (< 20 cm of water) help prevent this complication.

Endoscopic resection and treatment of upper urinary tract urothelial tumors

Conventional treatment of upper tract urothelial lesions is based on radical open surgery, ie, nephroureterectomy and resection of a bladder cuff or segmental ureterectomy. In patients with severe comorbidities, bilateral tumors, or solitary kidneys, renal-sparing surgery is an option. Endoscopic treatment is performed ureteroscopically or through a percutaneous tract. Electrocautery and/or laser energy is used for tumor resection and/or coagulation in a fashion similar to that of standard transurethral resection of bladder tumors. Postoperatively, topical chemotherapy (ie, mitomycin-C, thiotepa) may be instilled via a nephrostomy tube or ureteral catheter to reduce recurrence rates. Although safe, confirmation of the effectiveness of this immediate adjuvant topical therapy awaits the results of large trials.

The retrograde ureteroscopic approach is favored over percutaneous endoscopic therapy because it is less invasive and avoids the possibilities of percutaneous tract seeding. In select cases with large tumor burdens, a mature nephrostomy tract may help facilitate clearance. Success with both forms of treatment is based on the presenting tumor grade and stage. Low-grade urothelial tumors are associated with the best outcomes with these treatments. Close life-long endoscopic surveillance is required to detect any recurrences.

The kidneys are retroperitoneal organs that are obliquely placed as they lie on the anterior surface of the psoas muscles. The right kidney is often 2-8 cm lower than the left due to the presence of the liver on the right side. It lies adjacent to the 12th rib, liver, duodenum, and hepatic flexure of the colon. The left kidney is adjacent to the 11th and 12th ribs, pancreas, spleen, and splenic flexure of the colon.

The kidney may change location with changes in patient position and respiration. Normally, kidneys do not exceed 8-9 cm excursion when a patient stands from a supine position. With the respiratory cycle, the kidneys naturally move in a vertical direction. Due to the close proximity of the kidney to the pleural cavity, a risk of pleurotomy is incurred with a percutaneous puncture, especially during upper-pole renal access. To help prevent pneumothorax, percutaneous renal access above the 12th rib should be performed near the end of the rib.

The collecting system of the kidney is composed of minor calices (2-4), major calices, and a renal pelvis. The renal pelvis lies in the renal sinus and narrows at the UPJ to form the ureter. In the renal hilum, the vein is usually situated anterior and the renal pelvis is posterior, with the artery lying in between.

The only contraindication to percutaneous renal access is an uncorrected coagulopathy. Correcting any abnormalities prior to percutaneous access is essential. Thrombocytopenia should be corrected with platelet administration. For elective procedures, patients on warfarin (Coumadin) should have their coagulation factors normalized prior to surgery.

Preoperative considerations

A thorough history should be obtained and a physical examination should be performed prior to any percutaneous renal procedure.

Special attention should be paid to the following historical factors: anticoagulation, bleeding disorders, contrast-medium reactions, malignancy, obesity, spinal cord injury, and history of urinary tract infections with the urine cultures and sensitivities.

Coagulation profile

This includes prothrombin time, with international normalized ratio (INR), activated partial thromboplastin time, and platelet count.

The only contraindication to percutaneous renal access is an uncorrected coagulopathy. Correcting any abnormalities prior to percutaneous access is essential. Thrombocytopenia should be corrected with platelet administration. Aspirin and clopidogrel (Plavix) should be stopped preoperatively to allow for platelet function to be optimized.

For elective procedures, patients on Coumadin should have their coagulation factors normalized prior to surgery.

Overall renal function

This should be evaluated prior to performing percutaneous surgery. Typically, a blood urea nitrogen and creatinine suffice.

Complete blood cell count

A complete blood cell count is essential prior to performing percutaneous access.

Intraoperative and postoperative bleeding is a possible complication of percutaneous renal surgery, and knowledge of the patient's baseline hematocrit is critical in patient management if significant bleeding occurs.

In addition, the white blood cell count may indicate a concurrent infectious process requiring more aggressive antibiotic prophylaxis.

Urinalysis and urine culture

Prior to manipulation of the urinary tract, ruling out urinary tract infection is essential. Percutaneous manipulation of the kidney may rapidly lead to sepsis in the setting of infection and/or obstruction.

Appropriate antibiotic coverage is useful prior to the procedure and should be available during the procedure to help prevent intraoperative sepsis.

Patients with known infectious stone burdens may require staged therapy with percutaneous tract maturation, especially if resistant organisms are encountered on preoperative urine cultures.

Before placing a percutaneous nephrostomy, baseline diagnostic renal imaging is required. Intravenous or retrograde pyelography and renal ultrasonography are the most common imaging modalities used to define renal anatomy and pathology. Computed tomography, nuclear renography, and magnetic resonance imaging may all be used to define unexpected abnormalities. CT scanning may help reveal any posteriorly lying loops of colon that may overlie a potential nephrostomy tract and may help in planning a safe angle for nephrostomy tube placement. All radiographic studies should be carefully reviewed prior to placement of a nephrostomy tube. In patients with renal ectopy, malrotation, or a history of surgery that would change the perirenal anatomy, CT scanning is particularly useful in planning a safe percutaneous tract into the renal collecting system.

Both ultrasonography and fluoroscopy are useful when nephrostomy placement is planned and performed. Baseline ultrasonography provides useful information prior to the procedure, such as depth and lay of the kidney, location of stone burden, and the degree of hydronephrosis. Every percutaneous renal access procedure is performed with real-time imaging. Fluoroscopy is preferred when precise renal access is required, as with planned intrarenal endoscopic intervention.

Contrast medium–enhanced imaging is essential in defining the intrarenal collecting system. Intravenous pyelography may help define the caliceal system and stone burden if the kidney functions well and is not obstructed. If the renal function is suboptimal, retrograde ureteropyelography can help define the collecting system. Antegrade studies may be performed after initial access is obtained.

A 3-dimensional CT scan with reconstruction images can be used selectively in complicated cases, such as in planning a percutaneous approach to a staghorn calculus in a malrotated kidney or in revealing crossing vessels in a patient with UPJ obstruction. CT urography has recently been used to provide a very accurate anatomical roadmap.

Endoluminal ultrasonography may be used to diagnose and to evaluate the depth of penetration of ureteral and renal pelvic neoplasms, to locate crossing vessels and septa for guiding endopyelotomy of UPJ obstruction, and to identify submucosal calculi. Endoluminal ultrasonography is performed using small (6-10F) high-frequency transducers, which are inserted into a hollow viscus (ie, ureter).

Simple percutaneous renal access procedures are performed with the patient in the prone position while under a combination of local anesthetic and intravenous sedation. Patients who are morbidly obese and those with significant cardiopulmonary disease may not be able to sustain this position. A general anesthetic with endotracheal intubation may be preferable, especially in longer cases, to help avoid inadvertent aspiration. Appropriate medical consultation may be useful in these higher-risk patients.

A thorough history should be obtained and a physical examination should be performed prior to any procedure. Special attention should be paid to the following historical factors: anticoagulation, bleeding disorders, contrast medium reactions, malignancy, obesity, spinal cord injury, and history of urinary tract infections. Essential laboratory data include a coagulation profile, complete blood cell count, electrolytes, blood urea nitrogen, creatinine, platelet count, urinalysis, and urine culture. Appropriate antibiotic coverage before and on call during the procedure is useful in preventing intraoperative sepsis.

Simple percutaneous renal access procedures are performed with the patient in the prone position while under a combination of local anesthetic and intravenous sedation. This position may be hazardous to patients with severe cardiopulmonary disease (eg, chronic obstructive pulmonary disease) or those who are morbidly obese. Consultation with a pulmonologist or intensivist may be required. If more than a simple drainage procedure is planned, then a general endotracheal anesthetic should be used to protect the airway from aspiration (ie, vasovagal reaction).

Initial access

The ideal percutaneous nephrostomy tract should avoid surrounding organs and provide straight access to the desired calyx. Nephrostomy placement is usually performed under fluoroscopy or with the assistance of real-time ultrasonography. For percutaneous puncture of the renal collecting system, the patient should be placed on the fluoroscopy table in the prone position. The collecting system is then opacified via 1 of 3 techniques: (1) intravenous pyelography, (2) retrograde pyelography, or, if needed, (3) an antegrade ureteropyelography (ie, a 2-stick technique where a small needle is passed first and then a larger needle used for guidewire access.).

A standard lower-pole puncture site is along the posterior axillary line midway between the 12th rib and the iliac crest in the lumbar triangle (Petit triangle). Posterior calices, which project more medially than anterior calices, are preferred. Even though lower-pole access is often useful and may be adequate for drainage, upper-pole access is preferred for ureteral procedures. It is commonly performed above the 12th rib with a low rate of pneumothorax (< 3%). The first maneuver is positioning the access needle (18- to 21-gauge) over the desired calyx with posteroanterior fluoroscopy. The fluoroscope's image intensifier is then rotated 30° toward the operating surgeon so that the axis of the posterior calyx is parallel to the fluoroscopic beam. With the shaft of the access needle also in line with the oblique fluoroscopic beam, the tip of the needle is adjusted so it remains on the selected calyx. The needle is then advanced into the posterior calyx. See image below.

Direct percutaneous access to the renal pelvis should be avoided to prevent hilar injury. Successful puncture is determined by urine dripping from the sheath after the needle's stylet has been removed. Contrast is then injected through the sheath to opacify the collecting system. A guidewire is then passed through the sheath and coiled in the collecting system, as shown below. Narrow dilators and subsequently a small nephrostomy tube (6-12F) may then be placed over the guidewire if only simple renal drainage is desired. If a more invasive procedure is planned, dilation with either serial or balloon dilators may be performed to obtain a tract 24-30F in diameter.

Endoscopic intrarenal instrumentation

Nephroscopes are instruments that are inserted percutaneously through a nephrostomy tract. Standard rigid instruments are 19.5-26F in diameter and have rod lenses or fiberoptic imaging with offset eyepieces. Endoscopic lithotripsy is performed by applying a lithotrite through the central working channel. Available instruments include mechanical graspers and various lithotrites (eg, holmium laser, electrohydraulic, hollow-core ultrasonic or lithotriptors) and are complementary to the endoscope as long as they pass through the central channel. Actively deflectable, flexible nephroscopes are also used percutaneously through nephrostomy tracts. They are used to access calculi in calyces that cannot be reached by the rigid instruments and frequently can be deflected into most of the intrarenal collecting system. See images below.

Percutaneous treatment of renal stones

In the era of extracorporeal shockwave lithotripsy (ESWL), the indications for percutaneous treatment include (1) urinary obstruction not caused by the stone itself (eg, calyceal diverticulum, UPJ obstruction), (2) large-volume stones that are larger than 2.5 cm (eg, staghorn calculi), (3) stones that are not amenable to ESWL or ureteroscopic treatment (eg, anomalies of the kidney, pelvic kidney, obesity), (4) infectious stone burdens (eg, staghorn calculi), and (5) lower-pole calculi that are deemed inappropriate for ESWL.

When performing a PCNL (see video below), smaller mobile stones are removed via graspers, forceps, or flexible/rigid (Perc NCircle) wire baskets. Large dense stones are fragmented using ultrasonic, electrohydraulic, laser, or pneumatic energy. Ultrasonic techniques are preferred because they allow for stone fragmentation with simultaneous in-line suction through a hollow cylindrical probe that continuously removes sand and small fragments. However, ultrasonic lithotripsy can be performed only through a rigid endoscope because any deflection of the probe dramatically decreases the power of this lithotrite. Laser lithotriptors such as the holmium:yttrium-aluminum-garnet laser are particularly powerful and also may be used with flexible endoscopes that can access more of the collecting system but without simultaneous suction to clear debris.

The irrigation used during all percutaneous endoscopic treatments should be sterile warm isotonic sodium chloride solution. Irrigant may be absorbed during treatment via small veins. If significant fluid absorption is suspected, then diuretics (eg, mannitol, furosemide [Lasix]) should be administered intraoperatively.

Following completion of percutaneous endoscopic treatment, a nephrostomy tube should be placed through the tract, as shown below. The tube type selected depends on the need for future interventions. If repeat procedures are planned, then a reentry Malecot may be used. Other drainage tubes include Foley catheters and regular Malecot drainage catheters.

Success rates have been reported to be as high as 98-99% with PCNL. However, as the size of the stone burden increases, the stone-free rate with a single session drops. Repeat procedures or multiple nephrostomy access tracts may be required for large stone burdens. Repeat or staged surgery often is performed 36-48 hours following the initial procedure, after any bleeding has subsided and endoscopic visibility has improved.

Following percutaneous endoscopic procedures involving a significant amount of manipulation of the collecting system (eg, laser lithotripsy, endopyelotomy), urinary drainage is ensured with a nephrostomy drainage catheter and, on occasion, an additional internal ureteral stent. The catheters should be large enough to provide adequate drainage of the kidney and should be chosen relative to the size of the percutaneous access tract used for the surgical intervention. Venous sinus or access tract bleeding can be minimized with the tamponading nature of a large-caliber nephrostomy tube. Simple Foley drainage catheters may be left as a nephrostomy postoperatively, especially if no further endoscopic treatments are required. If staged endoscopic procedures are anticipated and a mature straight nephrostomy tract is required, then a reentry Malecot that combines a nephrostomy with a short ureteral stent is often used.

Postoperatively, patients should be monitored for bleeding, especially in the recovery room. If significant parenchymal bleeding occurred intraoperatively, the hematocrit should be checked and the patient should be appropriately resuscitated. Renal parenchymal bleeding can often be controlled postoperatively by clamping the nephrostomy tube for a short period in the recovery room. The simultaneous administration of diuretics (eg, mannitol, Lasix) and intravenous fluid increases the intraluminal collecting system pressure. If the bleeding is venous in origin, this maneuver stops it once the intrarenal pressure exceeds central venous pressure. Later, urine begins to drain from the nephrostomy as urokinase begins to slowly act on the intrarenal clot. Vigorous attempts at catheter irrigation in the immediate postoperative period only lead to blood loss and should be avoided, if possible.

Chest radiography should be part of the routine postoperative management due to the risk of a pleural tear or perforation when supracostal percutaneous access is obtained. If a pneumothorax or hydrothorax is present, pleurocentesis or placement of a small-diameter thoracostomy tube may be required.

Prophylactic antibiotics routinely are continued postoperatively until all tubes are removed and all puncture sites are healed.

Follow-up imaging and nephrostography are performed routinely after most therapeutic maneuvers, prior to nephrostomy removal. Antegrade studies allow assessment of most treatment outcomes. For example, the presence and location of residual stone material may be assessed, and the patency of the entire collecting system also may be assessed. Mild extravasation may be present at the nephrostomy site and along the tract, but other sites of extravasation secondary to perforations in the collecting system should be allowed to heal with catheter drainage prior to nephrostomy tube removal.

For excellent patient education resources, see eMedicineHealth's patient education article Kidney Stones.

Complications associated with percutaneous nephrostomy tube placement alone are uncommon and are usually minor in nature. When more extensive endoscopic maneuvers are used through a nephrostomy tract, the associated complications are more common and severe. The potential complications include the following:

• Acute bleeding requiring transfusion (< 5%): Bleeding may result from traumatized renal parenchyma or injury to a perinephric vessel. Intraoperative hemorrhage is best managed by immediate tamponade. Large nephrostomy tube placement is invariably effective. In rare cases, angiography with embolization or open surgery is needed (< 0.1%). Delayed bleeding after nephrostomy removal is uncommon (0.5%).

• Perforation of the collecting system (20-30%): This common finding, which often occurs with tract dilation, is managed by nephrostomy drainage. Within 24-48 hours, the urothelium seals, given that the collecting system is adequately drained.

• Pleurotomy/pneumothorax (< 5%): Usually associated with a supracostal approach, a pleural injury usually results in a hydrothorax and, infrequently, pneumothorax. Generally, it resolves with simple thoracentesis, but rarely, it may require chest-tube placement and drainage for 48 hours. Chest radiography is recommended following all percutaneous procedures in the recovery room.

• Sepsis (< 1%): Higher rates are noted in those with an infected stone burden. Parenteral antibiotics and nephrostomy drainage are required. Usually, a penicillin-derivative antibiotic and an aminoglycoside are used in combination for initial broad-spectrum coverage.

• Adjacent organ injury (< 1%): Injury may occur to the liver, spleen, duodenum, colon, and adjacent structures. Colonic injury is the most common of these and occurs when the nephrostomy is passed through a redundant portion of the colon before entering the kidney. In cases of colonic injury, management includes repositioning the nephrostomy catheter back until it is in the colon (ie, colostomy tube) and placing an external retrograde ureteral catheter to drain the renal pelvis. Generally, colostomy is indicated only for clinical peritonitis.

• Contrast reactions (< 0.2%): If a problem is anticipated, preoperative steroids (eg, prednisone) should be administered. Should a reaction develop, treatment includes termination of the examination, antihistamines, steroids, H1 and H2 blockers, plus epinephrine, if needed.

• Acute loss of the nephrostomy tract: This can usually be avoided with the use of a safety wire. If it occurs, the tract may be probed with a guidewire either in an antegrade or in a retrograde fashion; however, a repeat puncture may be required.

• Leakage from around a nephrostomy tube: Generally, this indicates some type of blockage. This may be caused by a blood clot, a piece of sloughed tissue, or compression of the tube by the flank musculature. Tube compression is more likely with a nephrostomy tube that is too narrow or too soft. Irrigation of the tube usually does not provide a permanent solution; therefore, replacement with a stiffer and/or larger tube is recommended and usually solves the problem.

Percutaneous surgery is associated with minimal patient morbidity compared to open surgery.

With the advent of percutaneous surgery, many conditions that at one time required major open surgical procedures are now treatable endoscopically. Initial percutaneous procedures were simple and included drainage of the upper tracts in the setting of obstruction and sepsis, along with diagnostic procedures. As the instrumentation has developed along with the techniques, percutaneous surgery is now used as a minimally invasive treatment option for large stone burdens, strictures, UPJ obstructions, and upper tract lesions.

Percutaneous surgery is now commonly used by urologists with minimal morbidity in comparison to open surgery. Because significant complications may occur, percutaneous manipulation should be used by those with experience.

The applications of percutaneous endoscopic renal surgery continue to expand. Advances that minimize morbidity and improve accuracy of percutaneous access are areas of current study. Future investigation involving new real-time imaging modalities, bioimpedance-based access needles, and robotic interface systems may ensure increased accuracy. These and other innovations will continue to develop and shape the field of percutaneous endourology well into the 21st century.