Typical CT appearance of renal colic with an obstructing stone at the left vesicoureteric junction associated with a degree of hydroureter, hydronephrosis and perinephric fat stranding. This is a very common location for a ureteric calculus to lodge. The vast majority of stones that are 4 mm or less will pass naturally into the bladder. This stone measures 5.5 mm, thus might require surgical extraction.