Re: Staghorn Morphometry: A New Tool for Clinical Classification and Prediction Model for Percutaneous Nephrolithotomy Monotherapy

H ats-off to the authors for describing a classification for staghorn stones using morphometry that could clinically predict tract(s) and stage(s) in percutaneous nephrolithotomy (PCNL). We have a few queries. The authors have excluded 38 patients because of renal insufficiency. In an earlier study by the same group, ¹ the authors maintain that “for those with compromised renal function, we obtain a non-contrast-enhanced 3D CT (NCCT), which helps us to assess the pelvicalyceal system, as well as the stone bulk and location.” We also think that NCCT will give adequate information that is needed for morphometry classification. Renal impairment is common (24%; ie, 38/163 in the present study itself ) in patients with staghorn stones, and this classification can be used in them also.

The authors classify type 1 staghorn with lesser than 5% unfavorable calix stone percentile volume while type 3 staghorn with greater than 10% unfavorable calix stone percentile volume and type 2 staghorn is in between types 1 and 3. At the same time, they mention that in type 2, “a smaller volume (<2% – type 2a) may result in single stage while larger volume (>2% – type 2b) may result in multiple stages.” These data seems ambiguous and need clarification. Also we would like to know the group to which a stone will belong if total stone volume is 20,000 mm³ but with less than 10% unfavorable calix stone percentile. Would it be staghorn type 2 or type 3?

We also treat a large number of patients with staghorn stones. From a practical point of view, however, we think that we may not change our practice after reading this article. We will still plan treatment after seeing the intravenous urography/computed tomography scan. Such classifications have a drawback of being cumbersome and turn out to be useful in the research setting only.