What are the Ultrasound findings of urinary obstruction?
US is often the first imaging study of choice in patients with newly diagnosed renal dysfunction in order to exclude an underlying mechanical obstruction. Diagnosing urinary obstruction sonographically is based on the detection of hydronephrosis. Sonographically, the dilated renal collecting system appears as multiple anechoic structures conforming to the expected location of the renal calyces in contiguity with a centrally dilated renal pelvis ( Figure 62-9 ). Bilateral hydronephrosis is usually due to obstruction at the level of the bladder. However, the cause of unilateral hydronephrosis due to obstruction of the ureter at or above the bladder can be difficult to delineate on US as the midureter is often not visible sonographically. Detection of hydronephrosis should prompt imaging of the bladder and visible ureter for the underlying cause of obstruction. The bladder should also be imaged with color Doppler technique to search for ureteral jets. The presence of a ureteral jet excludes complete urinary tract obstruction.