Comparison between ultrasound and noncontrast helical computed tomography for identification of acute ureterolithiasis in a teaching hospital setting

Abstract

Context and objective: Recent studies have shown noncontrast computed tomography (NCT) to be more effective than ultrasound (US) for imaging acute ureterolithiasis. However, to our knowledge, there are few studies directly comparing these techniques in an emergency teaching hospital setting. The objectives of this study were to compare the diagnostic accuracy of US and NCT performed by senior radiology residents for diagnosing acute ureterolithiasis; and to assess interobserver agreement on tomography interpretations by residents and experienced abdominal radiologists.

Design and setting: Prospective study of 52 consecutive patients, who underwent both US and NCT within an interval of eight hours, at Hospital São Paulo.

Methods: US scans were performed by senior residents and read by experienced radiologists. NCT scan images were read by senior residents, and subsequently by three abdominal radiologists. The interobserver variability was assessed using the kappa statistic.

Results: Ureteral calculi were found in 40 out of 52 patients (77%). US presented sensitivity of 22% and specificity of 100%. When collecting system dilatation was associated, US demonstrated 73% sensitivity, 82% specificity. The interobserver agreement in NCT analysis was very high with regard to identification of calculi, collecting system dilatation and stranding of perinephric fat.

Conclusions: US has limited value for identifying ureteral calculi in comparison with NCT, even when collecting system dilatation is present. Residents and abdominal radiologists demonstrated excellent agreement rates for ureteral calculi, identification of collecting system dilatation and stranding of perinephric fat on NCT.

Figure 1. Localization of the 40 ureteral stones founded on noncontrast helical computed tomography of 52 patients.

Figure 2. 33-year old man with right-sided renal colic. Noncontrast helical computed tomography (CT) and abdominal ultrasound (US) in the same patient. (a) Coronal identification of the right kidney (between calipers) with a renal stone and mild intrarenal collecting system dilatation. The same findings were found on CT scan (b). In the US scan of the bladder and right ureterovesical junction (c), the radiology resident did not find the small stone (3 mm), shown in CT (d).

Figure 3. Comparison between ultrasound (US) and computed tomography (NCT) in two different patients. (a) Coronal identification of the left kidney showing collecting system dilatation, which was confirmed in NCT (b). US scan at bladder level showing stone at left ureterovesical junction (arrow in c), confirmed by NCT (d).

Figure 4. Collecting system dilatation. Noncontrast helical computed tomography (NCT) on a patient with a stone in the distal left ureter, showing ureteral dilatation in comparison with the contralateral normal side (arrows).

Figure 5. Ureteral fat stranding. Axial slice in noncontrast helical computed tomography (NCT). Stone identified in the proximal right ureter (arrow), associated with ureteral wall edema (tissue rim sign) and perinephric fat stranding. A stone in the kidney is also identified (arrow head).