Comparison of nuclear renographic renal cortical transit time with diuretic drainage time parameters in congenital hydronephrosis.

INTRODUCTION: Ureteropelvic junction obstruction (UPJO) is a frequent cause of congenital hydronephrosis (CHN). There is no gold standard diagnostic test for UPJO. Serial diuretic renogram is often used as a surrogate for diagnosing UPJO. Cortical transit time (CTT) is a renogram parameter reported helpful for management. Our primary objective was to study the association of CTT with other diuretic renogram parameters, and secondarily with clinical management.

METHODS: We retrospectively reviewed 295 charts for CHN and pyeloplasty. We included 64 consecutive pyeloplasties (treatment group), and 44 conservatively managed CHN with available diuretic renogram (conservative group). Excluded were 55 patients >1 year old at presentation and 133 patients with other urinary abnormalities or incomplete data. Pyeloplasty indication profile included worsening hydronephrosis, initial DRF ≤40 % with prolonged diuretic drainage time, decrease in DRF ≥5 %, prolonged diuretic drainage time and symptomatic. Ultrasounds (RBUS) were reviewed for HN grade and anterior-posterior diameter (APD). MAG-3 diuretic renograms were reviewed for differential renal function (DRF), CTT, diuretic half-time (T1/2) and global washout (GWO). Delta (Δ) CTT between the affected and contralateral renal unit was calculated.

RESULTS: Regarding T1/2, the cut-off with the highest area under the curve (AUC) on the ROC curves was CTT >5 min (AUC = 0.84) and Δ CTT ≥3 min (AUC = 0.91). Regarding GWO, the best cut-offs were the same: CTT >5 min (AUC = 0.88) and Δ CTT ≥3 min (AUC = 0.91). A cut-off of >3 min for CTT had the highest sensitivity for pyeloplasty (80 %) but poor specificity (55 %). CTT >5 min had the best specificity (96 %). A cut-off for Δ CTT of ≥3 min had the highest specificity for pyeloplasty (98 %).

CONCLUSIONS: Increasing CTT correlated with increasing diuretic drainage times and decreasing diuretic global washout. The previously reported cut-off of CTT >3 min was sensitive but not specific for impaired diuretic drainage times. We identified that a CTT >5 min and the novel Δ CTT ≥3 min were associated with significantly impaired drainage times. We conclude that a CTT greater than 5 min may be a better indicator of severity than 3 min. Similarly, a CTT <3 min is likely an indicator of a favorable outcome. These indicators of severity for children presenting with CHN could help tailor the frequency and type of follow-up imaging. Further prospective studies are required to validate these findings.