Introduction

Evidence-Based Review

However, routine use of CT for suspected renal colic has significant limitations. Patients are exposed to significant amounts of ionizing radiation when they undergo CT of the abdomen and pelvis,^6,⁷ which makes CT inadvisable during pregnancy and less appealing in the pediatric population. Because renal colic is a recurrent diagnosis, patients may eventually receive multiple CT scans over time, and cumulative radiation doses may rise to concerning levels⁸ and place patients at risk for cancer later in life. Additionally, radiologic imaging has been shown to be the largest contributor to the cost of hospitalization in patients with renal colic, with CT being the most expensive imaging modality.^9,¹⁰

Ultrasound offers a safe, noninvasive means of assessing for renal colic that does not subject the patient to any ionizing radiation. Traditionally, ultrasound has been thought to have only fair sensitivity (37% to 64%) for detecting stones and better sensitivity (74% to 85%) for the diagnosis of acute obstruction,¹ whereas CT has consistently shown sensitivity greater than 90% for the diagnosis of ureteral stones.¹^–⁴ Recent studies using modern ultrasound equipment in the hands of skilled operators have demonstrated comparable sensitivity (76% to 98%) of ultrasound for the detection of ureteral stones.¹¹^–¹⁴ Although specific stone location and size cannot always be determined with ultrasound, surrogate findings may have prognostic value in guiding patient management. One study showed that normal renal ultrasound findings in the setting of suspected renal colic predicted a very low risk (0.6%) for subsequent urologic intervention.¹⁵

The goal of bedside ultrasound is to identify unilateral hydronephrosis as an indirect sign of obstructing ureteral stones. In the emergency department setting, Rosen et al. demonstrated a sensitivity of 72% and specificity of 73% for the detection of hydronephrosis with bedside ultrasound.¹⁶ More recently, Gaspari and Horst reported a sensitivity of 87% and specificity of 85% for the diagnosis of hydronephrosis.¹⁷ These results are comparable to a sensitivity of 81% and specificity of 92% for bedside ultrasound performed by on-call urologists; however, this study evaluated other renal findings in addition to hydronephrosis.¹⁸ Although the specific size of the obstructing stone is not typically demonstrated on bedside ultrasound, the degree of hydronephrosis may correlate with the size of the obstructing stone. A 2010 study showed that no or mild hydronephrosis predicted smaller stone size (<5 mm) as opposed to moderate or severe hydronephrosis.¹⁹

Bedside ultrasound for the measurement of urinary bladder volume has been well described in the literature. Bedside ultrasound provides a quantitative assessment of bladder volume when evaluating for urinary retention in the emergency department setting and can guide the need for emergency catheterization.^20,²¹ Many studies have shown good correlation between sonographic bladder volume calculations and urine volumes obtained via catheterization.²²^–²⁴ In the pediatric population, ultrasound has been shown to predict patients with volumes sufficient for successful catheterization of urine samples (>3 mL).²⁵^–²⁸ This may help avoid multiple attempts at urinary catheterization, which can result in unnecessary patient discomfort and the potential for iatrogenic infection. Additionally, bedside ultrasound has demonstrated increased success rates during attempts at suprapubic aspiration when compared with traditional, landmark-based techniques.²⁹^–³¹