Indications for PCNL

SWL relies on stone fragmentation and propulsion of the fragments into the urinary bladder by urine flow and peristalsis. PCNL is therefore indicated when calculus fragmentation and passage would be suboptimal, so that the patient would not be rendered stone-free. The indications for PCNL are listed in Table 1.

Stone Size

As the size of stones increases to greater than 2 cm to 3 cm, the fragmentation efficiency with SWL decreases, necessitating multiple SWL attempts for complete breakup and, often, ancillary procedures to aid the passage of calculus particles (198-200).

Table 1 Indications for PCNL for Upper Tract Urinary Calculi

Stone size: large stones (greater than 2-2.5 cm), staghorn calculi Stone composition: cystine calculi, failure of fragmentation with SWL Urinary obstruction + stones: UPJ obstruction, ureteral strictures

Compromised urine drainage + stones: stones in dependent dilated calyces, stones in calyceal diverticula Abnormal body habitus Symptomatic stones during pregnancy

Certain removal of all calculous material important; e.g., for airline pilots Stones for which other treatment modalities have failed Stones in renal transplants Stones following urinary diversion

Abbreviations: PCNL, percutaneous nephrostolithotomy; SWL, shock wave lithotripsy; UPJ, ureteropelvic junction.

Therefore, for most large stones, including staghorn calculi, SWL is not the treatment of choice (Fig. 2). Only 30% to 35% of stones larger than 2.5 cm to 3.0 cm may be rendered stone-free with SWL, compared to 70% to 90% of those treated with PCNL (201). Furthermore, 60% to 75% of patients with stones greater than 2.5 cm in size treated with SWL require additional procedures such as repeat SWL, PCNL, ureteroscopy, PCN, or stone manipulation, compared to 30% of patients treated primarily with PCNL (198). There is also a direct correlation between the size of the stone being treated with SWL and the subsequent accumulation of stone fragments (steinstrassen) in the distal ureter. Fedullo et al. (202) reported that the prevalence of steinstrassen was 17% when the calculi being treated were smaller than 10 mm, 26% when stones were 10 mm to 19 mm, 61% when stones were 20 mm to 29 mm, and 57% when stones were 30 mm or larger. It should be noted that a single stone larger than 25 mm to 30 mm has a different significance than several stones that are each 5 mm. The former is initially better managed with percutaneous techniques, whereas SWL is better for multiple smaller stones that are scattered throughout the collecting system and therefore less accessible to percutaneous techniques. Although each stone may be targeted easily for SWL, the presence of multiple stones does decrease the efficiency of SWL and the stone-free rate when compared to that of a single small stone.

Staghorn Calculi

Staghorn calculi are most commonly composed of struvite and are associated with recurrent urinary tract infections. Complete stone removal is essential in these patients because failure to do so allows persistence of infection and the eventual regrowth of the stone (Fig. 2). Other stones that may occasionally have a staghorn configuration are cystine stones, uric acid stones, and, rarely, calcium oxalate monohydrate stones. Staghorn calculi can range in size from a surface area that is less than 250 mm2 to greater than 5000 mm2 (200).

The primary approach to staghorn calculi should be by PCNL. Branched stag-horn stones that fill the majority of the collecting system pose special problems in removal because stones located deep in infundibulae and calyces may be difficult to reach from the initial percutaneous tract or tracts. The most efficacious method of treating such staghorn calculi is by the so-called sandwich technique (203-205). PCNL is initially used to rapidly remove large volumes of easily accessible stone with ultrasonic or electrohydraulic lithotripsy ("debulking''). If infundibulocalyceal fragments are inaccessible from the nephrostomy tract by the usual endourological techniques, SWL is used to break up the small volumes of remaining stones, followed by PCNL to remove the residual fragments. Some advocate a second percutaneous procedure to remove the stone gravel because stone fragments have a tendency to remain in dilated collecting systems for prolonged periods. Others allow the stone fragments to pass spontaneously after adjunctive SWL (206,207).

PCNL followed by SWL and second-look nephroscopy, if necessary, has been shown to be the most cost-effective method of treating staghorn calculi (208). Martin et al. (209) reported that in their 97 patients with complete staghorn stones, 46% were treated with one session of PCNL alone, 40% in two stages (PCNL + SWL), 10% in three stages, and 4% in four stages. Patients treated in one or two stages were more likely to be stone-free than those treated in three or four stages.

In patients with partial staghorn calculi, monotherapy with SWL is an option. Lingeman (200) reported that patients with staghorn calculi that were less than 500 mm2 in size and with no dilatation of the collecting system could be made stone-free in more than 90% of cases with SWL alone. They cautioned, however, that such small-volume staghorn calculi are uncommon, making up only 3% of the stag-horn stones treated in their series.

If staghorn calculi are considered as a group, reported stone-free rates for PCNL alone vary from 71% to 86% (210,211), compared to 84.2% for PCNL with or without SWL (200). Even though the addition of SWL at first glance appears to confer little advantage over PCNL alone as far as the stone-free success rate is concerned, the combination of the two procedures minimizes or eliminates the need for multiple renal accesses as well as for secondary endourologic procedures.

Still, only a minority of staghorn calculi require the addition of SWL to PCNL. During initial PCNL, efforts should be made to remove as much stone material as possible. If residual stone material is unavoidable, efforts should be directed toward removing enough stone material so that the residual stone burden is less than 2.0 to 2.5 cm in diameter (and thus more effectively treated with SWL).

To summarize, the effectiveness of SWL monotherapy in treating staghorn stones is directly proportional to the stone burden (212), with stone-free rates of 91.7% for staghorn stones smaller than 500 mm2 and 51.2% for larger stones (213). In contrast, the efficacy of PCNL is excellent irrespective of stone size, except when extremely large staghorn calculi (greater than 2500 mm2) are treated, with stone-free rates of approximately 85%.

Urinary Obstruction/Compromised Urinary Drainage

Urinary stasis can predispose to calculus formation. Examples of stones forming in association with obstruction are those in patients with UPJ obstruction (Fig. 10), calculi in calyceal diverticula, and stones in dilated lower pole calyces, malrotated kidneys, ectopic kidneys, horseshoe kidneys, and in patients with obstruction due to renal cysts or other renal masses. Changes in ureteral caliber or course due to congenital anomalies (retrocaval ureter, crossed ectopia), previous surgery (uretero-lithotomy, ureteral reimplantation), and chronic obstruction with resultant tortuosity or retroperitoneal processes (retroperitoneal fibrosis, tumors) can also impede ureteral drainage, leading to stone formation in these patients as well.

Although SWL can successfully break up the calculi in these situations, the fragments are unlikely to pass even when the stones are extensively fragmented (214).

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