The Utilization of Ultrasound in the Diagnosis of Urolithiasis

Abstract

Ultrasound uses high-frequency sound waves to image internal structures. Ultrasound probes generally range from 2 to 20 MHz, with higher frequencies allowing greater resolution and lower frequencies allowing greater tissue penetration. As an imaging modality for urolithiasis, ultrasound is sensitive (81–96 %) and specific (100 %) for detection of renal stones and holds the additional benefit of not exposing the patient to radiation. To obtain the best diagnostic accuracy, patients should be rolled as necessary to improve viewing of the kidneys. A transvaginal exam may be performed to locate a distal ureteral stone. On ultrasound, renal calculi are visualized as curvilinear, echogenic foci with posterior acoustic shadowing. The use of tissue harmonics can help enhance shadowing of small stones. Renal ultrasound remains an effective means for detecting renal stones. Although computed tomography (CT) is more sensitive and readily available, ultrasound should be considered in evaluating renal colic in pregnant women, children, and patients in which a nonradiation technique is preferred.

Ultrasound is also used for percutaneous access for nephrolithotripsy or antegrade ureteroscopy and should be performed by radiologists or surgeons well versed in the procedure. A small amount of contrast diluted 50:50 is then injected through the needle to opacify the collecting system under fluoroscopy. Ideally, only echogenic-tipped needles should be used for puncture. If unavailable, roughening the needle with a scalpel will greatly improve visualization of the needle on the ultrasound image.