Introduction

The kidney and bladder are two of the most sonographically accessible organs. The evidence for using ultrasound to make lifesaving diagnoses in this application is not as apparent as it is for cardiac or aortic ultrasound (except, of course, if flank pain and hydronephrosis are the result of a rapidly expanding AAA – see Chapter 5). Indeed, it is accurate to say that CT is dramatically more sensitive and specific in detecting ureteral stones and that ultrasound has a very low specificity for identifying ureteral stones (1–4). However, despite the advantages of CT for nephrolithiasis, there is still a role for ultrasound in evaluating the urinary tract in the emergency setting. In the most straightforward case, US identification of mild or moderate unilateral hydronephrosis in a patient with known renal colic and normal renal function testing (and a normal aortic screening evaluation) can obviate further radiologic testing. Patients who have relative contraindications to radiation exposure (pregnancy, pediatric patients) can also have ureteral obstruction evaluated by ultrasound. Renal ultrasonography easily and rapidly obtains evidence for or against high-grade obstruction, thereby expediting decisions regarding management and disposition (5, 6).

In addition, determination of bladder volume is another important indication for urinary tract ultrasound. Before catheterizing a patient to evaluate for postrenal obstruction or urinary retention secondary to neurologic events, an ultrasound can give an estimation of bladder volume and indicate whether catheterization is even necessary. Pediatric patients can also have bladder volume evaluated with ultrasound.