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 is an appropriate starting point for learning point-of-care sonography in the acute care setting.
The primary focus of renal ultrasonography in the emergency setting is to assess for obstructive uropathy by identifying the presence or absence of hydronephrosis.1,2 As with other areas of point-of-care ultrasound (POCUS), physicians using the modality for this specific goal have begun to explore new indications for imaging the urinary tract. Ultrasound assessment of bladder volume and evaluation of bladder filling before catheterization are two such examples.3–8 Another important consideration that has arisen with the focused use of renal ultrasound is the identification and management of unexpected or incidental findings, such as masses and cysts.9–12
Renal colic is a common presenting complaint to the emergency department (ED). Approximately 11–16% of men and 7–8% of women will experience symptoms related to urolithiasis by the age of 70. The presence of stones has more than doubled since 1994 when it was only 5.2%. Since there is an associated morbidity with urolithiasis, prompt and proper diagnosis is necessary.7,8 Historically, intravenous pyelogram (IVP) was used for cases of suspected renal colic. IVP, which includes the use of iodinated contrast material and exposes the patient to ionizing radiation, is more specific than ultrasound for the detection and characterization of a ureteral stone13–16; however, it has several disadvantages in the emergency and acute care settings. Noncontrast spiral computed tomography (CT) and ultrasound have largely replaced IVP as the preferred imaging studies for patients presenting with renal colic in the ED.16–18
The sensitivity of CT scan in the detection of renal stone disease varies from 95% to 100%.8,16,19–21 CT provides excellent visualization of the urinary tract and renal stones. It has a higher sensitivity for calculi as compared to ultrasound.22 However, CT may be less accessible at times, involves considerable exposure to ionizing radiation, and does not need to be performed emergently in stable patients with uncomplicated clinical presentations. Many physicians are presently using CT as opposed to ultrasound for better visualization of the urinary tract as well as extraurinary structures like the appendix and aorta. A retrospective analysis of ED visits from 1996 to 2007 found a 10-fold increase in the use of CT in patients with suspected renal stone disease.23 However, there was no corresponding increase in the proportion of renal stone diagnoses, alternate diagnoses, or hospital admissions. Another study showed that in patients who had resolution of pain with analgesics, immediate imaging by CT in the ED did not lead to reduced morbidity when compared to imaging by CT 2–3 weeks later.24 A comparative effectiveness trial published in ...