What Factors Drive Staghorn vs Nonstaghorn Pattern Growth in Patients with Metabolic Stones?

Purpose: There has been an increase in the number of staghorn calculi that form in the absence of infection (metabolic staghorns). It is unknown why some large metabolic calculi form as solitary or multiple separate, nonbranching caliceal stones, whereas others develop as staghorn stones forming a cast of the collecting system. We sought to compare these two groups of metabolic stone formers (SFs) in an attempt to shed light on these disparate stone-forming phenomena. Materials and Methods: From January 2017 to September 2018, 190 patients underwent percutaneous nephrolithotomy for stones >2 cm. We identified 86 (45%) patients with a metabolic stone, defined as ≥80% calcium oxalate monohydrate or dihydrate and/or calcium phosphate. Exclusion criteria included stones composed of cystine, >20% uric acid, or any infectious element (struvite or carbonate apatite). Metabolic staghorn and nonstaghorn SFs were compared with respect to medical comorbidity, 24-hour urine parameters, stone and urine microbiology, stone compositions, and intraoperative findings. Statistical differences were assessed using chi-square analysis, Fisher's exact test, and Student's t-test. Results: In total, 25 (29%) staghorn and 61 (71%) nonstaghorn SFs were included for analysis. The groups were statistically similar in age, sex, body mass index, and medical comorbidity. Staghorn SFs had larger stone burdens (p < 0.0001), but did not require more punctures (p = 0.783). Staghorn SFs were more likely to have hyperoxaluria (p = 0.041) and higher mean 24-urine oxalate levels (p = 0.040). There were no other significant differences in 24-hour urine profiles, rates of metabolic abnormalities, stone compositions, stone or urine cultures, presence of collecting system obstruction, or pelvicaliceal anatomy. Conclusions: Although potentially driven by urinary oxalate, whether a metabolic stone will form into a staghorn configuration or not does not appear significantly influenced by standard determinants of stone development, including metabolic profile, cultures, hydronephrosis, and pelvicaliceal anatomy, among others. Further work is needed to elucidate the physicochemical factors that govern the pathogenesis of this increasingly prevalent entity.

Does leaving residual fragments after percutaneous nephrolithotomy in patients with positive stone culture and/or renal pelvic urine culture increase the risk of infectious complications?

The residual fragments in patients with preoperative and intraoperative culture positivity may serve as an infection focus. The aim of this study was to assess the importance of residual fragments for developing SIRS in patients with stone culture and/or RPUC positivity. After obtaining institutional review board approval, a total of 729 patients who undergone PCNL for renal stones were included in this study. Residual fragments accepted to be positive if any fragment was detected irrespective of size. All patients were followed-up postoperatively for SIRS criteria. The patients were then followed-up for residual stone-related events and infectious complications. 94 of the 729 patients have developed SIRS postoperatively. SIRS positivity was more common among males and found to be associated with higher stone burden and presence of staghorn stone. Patients with residual fragments after PCNL also had higher rates of SIRS. In the subgroup analysis of 203 patients who had post-PCNL residual fragments, the peroperative stone and/or RPUC positivity was not found to be associated with the development of the SIRS. Although presence of residual fragments after PCNL is associated with SIRS development, stone culture and/or RPUC positivity has no additional risk for development of post-PCNL infectious complications in patients with residual fragments.