Although it was first described more than a decade ago, the place for mini-PCNL within the range of stone interventions has yet to become firmly established.
This single surgeon, prospective case-control series from a high-volume centre has demonstrated that mini-PCNL offers no difference in stone free rates to standard PCNL for stones 1–2 cm in size, but is associated with a shorter hospital stay, despite taking longer in theatre (due to the length of time required for laser stone fragmentation) .
These findings are supported by a recent, similar-sized and designed study in which Knoll et al reported that operative time and stone free rates were comparable between mini- and standard-PCNL, again with an advantage for significantly shorter hospital stay . These authors found mini-PCNL was associated with less pain by Visual Analogue Score, but like Mishra's study, showed no significant difference in total analgesia requirements, which was one of the anticipated benefits of mini-PCNL when it was first introduced.
The main advantage of mini-PCNL is the likelihood of a shorter hospital stay, which may be a consequence of fewer nephrostomies used in these patients. Whereas Knoll's protocol was to place a 22Fr nephrostomy after all standard PCNLs, Mishra's study left this decision to the operating surgeon's discretion. Whilst there is, of course, the potential for bias with this approach, this is somewhat mitigated by being a single-surgeon series with clear criteria for a “tubeless” procedure.
It is important to appreciate that “Mini” PCNL does not imply that this is a substantially less invasive procedure than standard PCNL – indeed, the complication rates for mini- and standard PCNL in both Mishra's and Knoll's studies were equivalent , and the levels of acute-phase markers (as a guide to the degree of surgical tissue damage) have been shown to be comparable between these procedures .
10 years on, the ultimate role for mini-PCNL remains to be determined, and with ongoing advances in flexible ureterorenoscopy, this genuinely less invasive modality may continue to emerge as the more serious challenger to conventional PCNL for renal stones of 1–2 cm.