Background:
Ureteropelvic junction obstruction (UPJO) is the most common pathological cause of antenatal and neonatal hydronephrosis. In this study we evaluated the proportion of collagen deposition to smooth muscles of obstructed ureteropelvic junction and its relation to the age at the time of diagnosis and to the postoperative complications.

Material and methods:
Fifty-five patients diagnosed antenatally or postnatally with idiopathic UPJO were recruited for the study. The age ranged from 1 month to 12 years. All the patients underwent the Anderson and Hynes pyeloplasty and biopsy samples were sent for histopathological examination and collagen assessment.

Results:
The median age of enrolled patients was 38.9 (1-144) months. Male to female ratio was 2.1:1. 65.5% patients had UPJO on the left side while 23.6% patients was right-sided and remaining 10.9% cases were bilateral. A significant association was found between collagen deposition and age at diagnosis. No significant relation was demonstrated between collagen deposition and postoperative complications.

Conclusions:
Based on the finding, it could be recommended that management for UPJO should be concentrated at an early age without any delay taking into account the clinical perspectives of various management techniques for the pediatric populations to avoid further complications.