The kidney and bladder are two of the most sonographically accessible organs. Both are easily recognizable to those who are new to ultrasound and thus the urinary tract can be a simple starting point for learning-focused sonography in the acute care setting.
The primary focus of renal ultrasonography in the emergency setting has been to determine the presence or absence of hydronephrosis.1–4 As with other areas of emergency ultrasound, physicians using the modality for this specific goal have begun to explore new indications for imaging the urinary tract. Ultrasound determination of bladder volume and evaluation of bladder filling before catheterization are two such examples.5–14 Another important consideration that has arisen with the focused use of renal ultrasound is the management of unexpected or incidental findings, such as masses and cysts.15–18
For many years, the standard investigation in cases of suspected renal colic was the intravenous pyelogram (IVP). Although IVP is more specific than ultrasound for the detection and characterization of a ureteral stone,19–23 it has several disadvantages in the emergency and acute care settings. Intravenous contrast dye, even in low ionic formulation, carries a small but real risk of allergy and nephrotoxicity.24–27 For this reason, in patients with known allergy to contrast, diabetes mellitus, renal insufficiency, or pregnancy, renal ultrasound or computed tomography (CT) becomes the preferred modality. Although routine determination of renal function tests in patients presenting with flank pain and hematuria is controversial, many radiology departments require these measurements before an IVP can be performed.
Ultrasound can be performed safely and quickly at the bedside with essentially no risks. Although it does not give information about renal function, the presence of unilateral hydronephrosis or hydroureter in the setting of hematuria and acute flank pain is very sensitive for the presence of a ureteral stone. Recent studies that combine the use of emergency renal ultrasound with a single plain abdominal film have found a sensitivity of 64–97% using IVP as a comparative standard.19, 20, 22, 23, 28, 29 Moreover, the degree of hydronephrosis, in combination with the patient's history, is helpful to determine the need for urgent consultation with a urologist. In this respect, bedside ultrasound often provides sufficient information to efficiently guide the treatment and disposition of the patient. Whereas a patient with mild to moderate hydronephrosis can, with few exceptions, be managed on an outpatient basis, the presence of severe hydronephrosis should prompt urgent consultation or close follow-up and further definition of the obstruction by CT.
Furthermore, ultrasound has the added value of providing anatomical information and identifying abnormalities that may be missed on IVP. In the course of utilizing ultrasound of the urinary tract to detect obstruction, practitioners are identifying other such abnormalities with increasing frequency. Some of these represent life- or kidney-threatening processes and may prompt timely definitive treatment. Ultrasound is especially sensitive for the presence of cysts and ...