Confirmatory imaging is not mandatory for all patients with a suspected kidney stone. Patients with known urolithiasis, no risk factors for complications (i.e., single kidney, immuno-compromised, renal transplant), a typical presentation, and ensured follow-up may be considered for outpatient treatment with pain control and possible expulsion therapy. CT is the study of choice and has demonstrated specificity nearing 100% and sensitivity of 95%. CT cannot image indinavir stones. In multiple reports KUB has a sensitivity in the range of 40% to 60%.
In 62 patients, US was used to follow the ureter to the level of the stone. The stone was identified as an intraluminal echogenic focus with shadowing (seen in all cases). Ultrasound is limited in the middle third of the ureter usually due to bowel gas. A change in position and compression can overcome this problem. In another study that evaluated 120 patients with renal colic using US, after plain radiograph to guide ultrasound imaging, a 95% sensitivity and 67% specificity was obtained.
Follow up imaging with ultrasound:
Recurrence of symptomatic kidney stones at 5 years is 50%, and at 10 years is 60%. In an imaging follow-up study of 158 patients with CT-diagnosed ureteral calculi, trans-abdominal US was compared to plain film or CT. The position of the stone on US had an accuracy of 94% and specificity of 99%. The authors concluded that ureteral calculi within 35 mm of the UVJ can be accurately followed using trans-abdominal US.
Autumn Graham, Samuel Luber, Allan B. Wolfson. Urolithiasis in the Emergency Department. Emergency Medicine Clinics of North America – Volume 29, Issue 3 (August 2011)
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