<unk>  is the most common upper urinary tract anomaly, affecting nearly 15% of the population.   
Embryologically occurs when 2 separate ureteric buds arise from a single wolffian duct. The future lower pole ureter separates from Wolffian duct earlier and migrates superiorly and laterally as the urogenital sinus grows.
Weigert-Meyer rule for bladder insertion: the upper pole ureter inserts inferior and medial to lower ureter.
Alternatively, the 2 ureters may fuse to form a single ureter prior to inserting into the bladder, termed a bifid<unk> .
The lower pole<unk>  is usually dominant, while the upper<unk>  may drain a single or few calices.
The upper pole ureter may demonstrate a ureterocele, which is associated with ureteral obstruction and recurrent UTIs in children. The upper pole ureter may also be ectopic or stenotic.
Duplicated collecting system
Ureteropelvic junction obstruction
Urethral caruncle
Ejaculatory duct obstruction
Dissection of the renal arteries
Multicystic dysplastic kidney
Metanephric adenoma pathophysiology
Renal urea handling