Describe the findings on ultrasound examination in urinary obstruction.

The central echo complex spreads apart. Dilated calices can resemble multiple renal cysts, but unlike cysts, they show continuity with the renal pelvis. Proximal ureteric dilation is often seen, but dilation of the distal ureter is often obscured by overlying bowel. It is often not possible to determine the cause of urinary tract obstruction during ultrasound examination.