Transient minimal hydronephrosis on contralateral kidney in infants with unilateral hydronephrosis: Is it an early sign of worsening of the affected kidney?

The criteria for surgical management of ureteropelvic junction obstruction are not well-defined, and there is a risk for loss of renal function before the operation. In this context, certain changes in contralateral kidney had been investigated in order to increase the sensitivity of diagnosis. In this study, we aimed to investigate whether contralateral transient minimal hydronephrosis (CTMH) can be considered as an “early alarm” sign for worsening of the affected kidney in infants with hydronephrosis. A total of 182 infants (92 surgically treated and 90 conservatively followed-up) with unilateral hydronephrosis were retrospectively analyzed. Ultrasonography and renal scan findings were evaluated. Correlation between the appearance of CTMH, contralateral compensatory hypertrophy (CCH) on ultrasonography, and prognosis of the affected kidney were evaluated. Among the surgically treated patients, 18 (19.6%) patients developed CTMH on average 7 months (0–13 months) before surgery. Among these 18 patients with CTMH, 12 patients (66.6%) had loss of renal function preoperatively, while this ratio was 29.7% on their counterparts (p = 0049). CCH was observed in 31 (33.7%) individuals in surgically treated patient group including all 18 patients with CTMH, while none of the conservatively followed-up patients developed CCH and/or CTMH. In the multiple logistic regression analysis, among the variables investigated, CTMH was found as an independent predictor of the deterioration in the affected kidney and of the poor prognosis (p = 0.011 and p = 0.0004, respectively). In our study, among the variables investigated, CTMH was found as an independent predictor of the deterioration in the affected kidney and poor prognosis in infants followed-up with isolated unilateral hydronephrosis. Additionally, CTMH can be considered as an “early alarm” sign for worsening of the affected kidney and the need for surgical intervention.