CTT on Renogram as an Early Marker of Significant Obstruction in Uretero-pelvic Junction Syndrome

Antenatal hydronephrosis (ANH) is an uropathy characterized by a dilatation of the renal collecting system. It is the most common abnormality found during prenatal ultrasound examination (1-5% pregnancies). Though the majority of cases are transient or "functional" and ultimately resolve after birth, some cases have a pathological origin of which ureteropelvic junction obstruction (UPJO) is the most common (7-35% cases).

An increased understanding of the natural history of ANH has been accompanied by a change in its management from systematic surgical approach to active surveillance and selective surgery. The main challenge is then to differentiate reversible ANH from pathological UPJO. Pathological obstruction generally results in an impairment of urine flow which, if left untreated, will result in renal damage or abnormal development of the kidney. It is therefore up to the paediatric urologist to determine whether the obstruction is significant before any irreversible damage occurs. However, without reliable prognostic criteria identified to date, controversy still exists regarding the indication and optimal timing for surgical management of UPJO.

Diuretic renography is currently the most widely used diagnostic modality to evaluate renal function and obstruction. It confirms significant obstruction when it demonstrates alteration of renal function, but having to wait for significant and potentially irreversible loss of function to be able to confirm surgical indication is unsatisfactory.

For many authors increase in hydronephrosis, defined as an increase in the dilatation of antero-posterior renal pelvic diameter (APRPD), is a marker of significant obstruction. But again, having to wait for an increase in hydronephrosis, which is by definition deterioration of the kidney, even if it precedes loss of function, remains unsatisfactory and therefore an earlier marker is needed to improve patients' management.

Determining a reliable early predictive marker for future deterioration of renal function in children with UPJO will considerably change current management of these children by avoiding unnecessary surgery for reversible cases and by being able to offer early surgery before renal deterioration for pathological cases. It could also determine which patients need close surveillance and which do not need to be monitored as often.

Two potential markers have been recently described: the cortical transit time (CTT) measured on renogram, which was shown in a recent retrospective study, to be associated with the need or not for surgery, and positional variation in APRPD as measured by sonography, which was also found to have prognostic value in a recently published pilot study. Both criteria are promising but need to be evaluated prospectively in larger population.

The investigators propose to study prospectively the prognostic value of CTT and as a secondary objective, to determine the prognostic value of positional variation in APRPD. The investigators will then be able to compare these two prognostic markers.