Diagnosis of Stones
Ultrasonography

Ultrasonography has become increasingly important technology for the detection of renal calculi. The sensitivity of ultrasonography is slightly superior to that of plain abdominal films. The renal calculi are detected by their marked echogenicity and associated acoustic shadowing. The minimal size of calculus that are detected or identified is at least 0.5 cm. with a transducer between 2.25 and 3.5 MHz. Transducers in the range of 6 - 10 MHz are able to detect renal calculi as small as 3 mm.

Normal kidney. Longitudinal section of the kidney (yellow arrowheads). The renal sinus is seen as an echogenic central zone. The cortex of the kidney is hypoechoic.

Renal ultrasonography is another imaging modality, which offers anatomical details of anatomical details without exposure to radiation or contrast material. The protection of the renal calculus is based on the presence a of highly echogenic focus with posterior acoustic shadowing of the stone. Renal ultrasonography is a useful screening tool for the demonstration of renal stones and evaluation of hydronephrosis in patients with suspected renal calculi. In most institutions, ultrasound for the detection of renal calculi is useful for patients where intravenous contrast or radiation is contraindicated. However, ultrasound is seldom utilized in the initial evaluation of patient with flank pain.

Renal calculus. Renal ultrasound demonstrating echogenic focus (red arrow) with an associated acoustical shadow (yellow arrowheads).

Advantages of Ultrasound

1. Good anatomical detail of the kidney in a short period of time.
2. No exposure to radiation.
3. No use of intravenous contrast agents.
4. Ultrasound is regarded as safe in obstetric patients.

Disadvantages of Ultrasound

1. Poor visualization of calcifications or obstructing stones in the ureter.
2. Lack of assessment of renal function.
3. The need for a full bladder to properly visualize stones at the ureteral vesicle junction (UVJ).
4. Limited role in the diagnosis of other pathology in the absence of a ureteral calculus.

Suggested readings
Laing FC, Jeffrey RB Jr., Wing VW: Ultrasound versus excretory urography in evaluating acute flank pain. Radiology 1985; 154(3): 613-616.

Deyoe IA, Cronan JJ, Breslaw BH, et al: New techniques of ultrasound and color Doppler in the prospective evaluation of acute renal obstruction. Do they replace the intravenous urogram? Abdom Imaging 1995; 20(1): 58-63.

Svedstrom E, Alanen A, Nurmi M: Radiologic diagnosis of renal colic: The role of plain films, excretory urography and sonography. Eur J Radiol 1990; 11(3): 180-183.

Aslaksen A, Gothlin JH: Ultrasonic diagnosis of ureteral calculi in patients with acute flank pain. Eur J Radio 1990; 11(2): 87-90.

Yilmaz S, Sindel T, Arslan G, et al: Renal colic: Comparison of spiral CT, US and IVU in the detection of ureteral calculi. Eur Radiol 1998; 8(2): 212-217.

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