We would like to thank Jason B. Wynberg for the useful comments about our technique. We have performed >80 ureteroscopy assisted retrograde nephrostomy (UARN) procedures for percutaneous nephrolithotomy since our initial report of UARN. These cases included: four patients that had renal stones in the lower calyx with horseshoe kidneys, three patients with complete staghorn calculi, a patient after anatrophic nephrolithotomy, a patient that had incomplete double ureter, obese patients, and patients after urinary diversion [1-6].

A rigid needle has a potential risk for injury. We have made some minor changes since our initial report [7]. First, we dilate using the rigid needle, which is included in the retrograde nephrostomy kit, to the renal pelvis not to the ureter. The puncture wire is grasped at the skin, and we reinsert the ureteroscope (URS) beside the puncture wire. The nephrostomy is dilated by rigid needle dilatation and catheter dilatation
up to 12 F, while ensuring that the dilator does not reach the ureter under visualisation with the URS. We insert the 12-F safety catheter to the ureter and we insert the guidewire beside the ureteric access sheath (UAS). Therefore, there is no additional
need for re-inserting the UAS. We only insert the 12-F safety catheter to the ureter; however, no injuries have occurred in our experience. Second, we do not insert the puncture wire with the cover. The coating cover occupies the inner lumen of the URS, because of low irrigation flow; clear visualisation has not been achieved. We insert the puncture wire from the distal
end to the proximal end of the URS, to avoid damage to the inner lumen of the URS.

We used the technique with a coaxial catheter that the author described in
one patient and we had no problem avoiding higher tension on the renal parenchyma and PUJ. We treated another two patients that had a hard capsule with our technique and we could not puncture toward the skin. A coaxial catheter might help avoid injury, in particular for the patients who are punctured at the lower calyx. However, rigid needle dilatation is necessary to dilate the capsule in patients with a hard capsule. The technique of retrograde puncture is still developing, so various changes may be needed to establish the best technique.