90% of urolithiasis are radio opaque, however their detection on a simple abdominal radiography is about 45%. The sensitivity of the ultrasound may vary between 60% and 80% depending on the size and location of urolithiasis and whether they are accompanied by obstructive phenomena. The sensitivity of ultrasound will be greater if the stone is located at the junction of ureterovesical or pyeloureteral as opposed to the average path of the ureter. Missed urolithiasis at ultrasound are generally ≤ 5 mm (majority between 2-3 mm). They have a good probability of spontaneous expulsion.