Moreover, a large round gas collection was found in the bladder, and a 1.1 x 0.9-cm calculus revealed a right distal ureter, leading to mild unilateral hydronephrosis and ureterectasis (Fig.
(8) Because pelviectasis and ureterectasis can take hours to develop, US will miss more than 30% of acute obstructions in patients who are not fully hydrated and is therefore not recommended as a first-line imaging modality.
It takes many hours for pelvicaliectasis and ureterectasis to develop therefore US will miss 30% of acute obstructions caused by a ureteral stone if patients are not specifically hydrated.