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

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.

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.

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 %).

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.