We examined 63 pediatric kidney stone patients presenting with a total of 142 stones to the Stollery Children’s Hospital from 1990 to 2013. Using univariate and multivariate analysis we assessed for either patient or stone characteristics that predicted surgical intervention for the calculi. We found two independent variables predictive of surgical intervention; stone size larger than 6 mm and stone type. Patient age and stone location did not predict surgical intervention. We suggest therefore that stone size and composition be considered in patients presenting with urolithiasis when deciding whether to remove the calculi electively in pediatric patients.
Thus far, factors that increase incidence or recurrence of pediatric urolithiasis have been examined. However, whether these factors are predictive of surgery has not been assessed. Similar analysis to ours in adult populations found that stone size is the most consistent predictor of the need for surgical intervention [13, 14]. To the best of our knowledge, stone type has not been examined as a predictor of surgery. In the absence of pediatric-specific literature, adult guidelines have been extrapolated to pediatric patients such that stone size less than 10 mm can be observed and medically managed as symptoms are tolerated [15]. Given the lack of pediatric literature on predictive factors for surgical intervention, we believe that our findings provide novel insight.
Several recent studies, including a systematic review by Tasian et al., found that the most common metabolic abnormalities associated with repeat renal stone formers are hypercalciuria and hypocitraturia [16, 17, 2]. Pietrow et al. found that children with these metabolic abnormalities were 5-fold more likely to form recurrent or multiple stones [7]. Kovacevic et al. studied specific metabolic risk factors for developing urolithiasis and found hypocitraturia to be the most significant, observing it in approximately 60 % of children with stones [18]. Although we found that metabolic abnormalities, likely leading to stone formation, were common in our cohort, they did not predict surgical intervention for a stone.
We identified four different stone presentations at diagnosis: hematuria, flank pain, urinary tract infection, and incidental. Of these, although not statistically significant (p = 0.06), hematuria was the most indicative of surgical intervention. However, 85–90 % of children with urolithiasis present with hematuria [19, 20]. Given the high prevalence of hematuria in pediatric nephrolithiasis patients, we do not feel that hematuria alone is specific enough of an indicator to warrant surgical intervention.
Van Savage et al. proposed that non-obstructive stones less than 4 mm in diameter should be observed and medically managed [21]. Pietrow et al. had similar findings with only 1 stone greater than 5 mm passing spontaneously [7]. Indeed, we found that the average stone size in the no-surgery group was 4.8 mm while those in the surgery group was significantly larger at 6.7 mm (p = 0008). This result persisted in multivariate analysis. Furthermore, we found that larger stone size at last follow up was also strongly associated with surgical intervention. Our results therefore strongly infer that stones less than 6 mm can be safely observed.
We found that stone composition associates with surgical intervention. The majority of calcium oxalate stones (91 %; p = 0.035) were surgically removed, while 78 % of the calcium phosphate stones passed spontaneously (p = 0.014). Kirejczyk et al. found that calcium oxalate stones showed a strong association with the metabolic risk factors hypercalciuria, oxaluria, magnesuria, and acidic urine - factors predisposing a patient to recurrent stone formation. In contrast, they found that calcium phosphate stones had a lower association with other risk factors including infection and impaction [22]. This suggests that calcium oxalate stones more often warrant surgical intervention due to their risk for causing complications and recurrent formation. Conversely, knowing that an individual is forming calcium phosphate stones supports more conservative management because they were more likely to pass without complications. Although of borderline significance, it was also noted that 7 of the 8 stones composed of uric acid, cysteine, or struvite were surgically removed. This finding is consistent with previous work that found struvite, cysteine and uric acid stones have unique durability and remarkable sizes that make passing the stone spontaneously unlikely [17].
Although we analyzed a significant number of stones in our cohort, this study has several limitations. The single center nature of the study would limit the total number of patients and reduce statistical power in the analysis. We performed much of the analysis at the level of the stone to increase power, however, there was clustering of stone factors within a given patient. We only had one child with a single kidney, which always had surgery, making conclusions on this population difficult. The duration of follow up was on average slightly less than two years, which limits the predictive power of this work. As this was a retrospective chart review we were limited by some missing data. Moreover, some stones that passed spontaneously were not collected, further reducing the number of stones we knew the composition of. Regardless, we have been able to identify factors predicting surgical intervention in children with urolithiasis.
