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 point-of-care 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 point-of-care 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 imaging modality 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, which include the use of iodinated contrast material and exposure to ionizing radiation. Noncontrast spiral CT and ultrasound have largely replaced IVP as the preferred imaging studies for patients presenting to the ED with renal colic.24–26
The sensitivity of CT scan in the detection of renal stone disease varies from 86% to 100%.27–35 CT provides excellent visualization of the urinary tract and renal stones, and has a higher sensitivity for renal calculi compared with ultrasound.36 However, CT remains less accessible, involves a considerable exposure to radiation, and does not need to be performed emergently in stable patients with uncomplicated clinical presentations. Many physicians are now using CT in place of both ultrasound and IVP because it allows visualization of the urinary tract as well as extraurinary structures such as 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.37 However, there was no corresponding increase in the proportion of renal stone 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.38 The widespread use of CT has raised concerns within the imaging community because of the large cumulative radiation dosage being delivered to patients. The successive and repetitive nature of renal colic virtually assures these patients (especially younger ones) a higher iatrogenic cancer risk and, thus, forms a logical argument for judicious use of CT in this population.39,40
Ultrasound, however, can be performed safely and quickly at the bedside with essentially no risks. It is the ...