Acutely obstructing ureteral stone without hydronephrosis

Axial noncontrast CT in a patient with acute left flank pain and hematuria (A and B) shows no hydronephrosis despite a mid-left ureteral stone (arrow). Due to persistent symptoms, a repeat scan 3 weeks later (C and D) shows mild left hydronephrosis and migration of the stone (arrowhead) to the left ureterovesical junction.