Authors' reply.

We wish to thank the readers for having gone through our article in detail and providing their critical appraisal. Their comments are very relevant and important, and we would like to answer them here.

First, regarding indication of intervention in small stones, as per the study by Koh et al., which has been quoted, in asymptomatic renal stones of average 5.7 mm size, only 20% had spontaneous stone passage whereas 45.9% had stone size progression.[1] Similarly, the second study by Coll et al. which has been quoted relates to ureteric calculi and says “The spontaneous passage rate for stones 1 mm in diameter was 87%; for stones 2–4 mm, 76%; for stones 5–7 mm, 60%; for stones 7–9 mm, 48%; and for stones larger than 9 mm, 25%.”[2] Our study included patients with renal stones of size 8–20 mm who were symptomatic and thus qualified for intervention.

Regarding case selection, as mentioned, the patients were selected on the specific indications such as presence of narrow infundibulum with calyceal stone, diverticular renal stone, stone refractory to shock wave lithotripsy (SWL), and failed retrograde intrarenal surgery (RIRS). In addition, case selection was based on patient's preference for percutaneous approach, which has also been mentioned in the article. All patients underwent due counseling, explaining all available options. The patients who opted for percutaneous approach, preferring one-stage clearance of the stone, and avoidance of double-J stent before or after the procedure, were taken up for the ultra-mini-percutaneous nephrolithotomy (UMP).

An additional factor was the treatment cost as in our system the cost of medicines and disposables is borne by the patient. Although it was not the subject of the present study, the difference in the cost of disposables in practical terms is significant between UMP and RIRS as has been documented as well.[3]

The comments are quite right in pointing out that according to the existing European Association of Urology guideline, percutaneous nephrolithotomy (PCNL) is a recommended therapy to treat large renal stone (>20 mm) and smaller stones (10–20 mm) of the lower renal calyx when unfavorable factors for ESWL exist, whereas flexible ureteroscopy was recommended in treating lower pole renal stone <20 mm. However, it needs to be remembered that these guidelines were framed on the basis of outcomes of standard PCNL and its morbidity. As the results of minimally-invasive PCNL keep coming in, with improved outcomes and reduced morbidity, the time is not far when a relook at the guidelines may become imperative. Further prospective randomized multicenter studies, which are already underway, will ultimately establish the place of minimally-invasive PCNL in the management of upper tract urolithiasis.