INDICATIONS

The principal indication for renal ultrasound is in the diagnosis of ureteral calculi, which, if they cause obstruction, will give rise to unilateral hydronephrosis. Less commonly, retroperitoneal processes (tumors, fibrosis) or pelvic pathology originating in the prostate, ovaries, or urethra may give rise to bilateral hydronephrosis. The indications for most emergency ultrasound evaluations of the urinary tract are one or more of the following:

1. Acute flank or back pain in

2. Hematuria

3. Urinary retention

Most of the findings discussed in this chapter are seen in the evaluation of such patients.

Renal ultrasound can identify calculi larger than 5 mm in diameter within the kidney. However, these stones do not cause symptoms of obstruction and are only clinically important if they become a nidus of infection or pass into the ureter. The ureter from the renal pelvis to the iliac crest is rarely visualized unless extremely dilated, and from that point to within a few centimeters of the ureterovesical junction (UVJ), is sonographically occult. Therefore, ureteral stones are usually diagnosed by inference from the presence of hydronephrosis. They are rarely seen per se, except when at the UVJ. Because some stones do not cause complete ureteral obstruction, they may not cause hydronephrosis, leading to a sensitivity of 75% for ultrasound alone in the detection of ureteral stones.