Diagnostic procedures – How does the urologist recognise kidney stones?

Sonography

Sonography, also referred to as ultrasound, is an easy-to-use method to obtain information about the kidneys and the ureter as regards the presence of stones, tumours and urinary obstruction. Even without using x-rays, this technique allows for an assessment of whether urinary stasis, i.e. obstruction of urine flow from the kidneys, is present, which can provide an indirect indication of the presence of stones in the ureter towards the bladder.

Kidney stones and stones just below the ureteropelvic junction can often be directly identified by sonography; however, this is usually difficult with stones of only a few millimetres in size.

Excretory urography

This is an x-ray imaging technique used to examine the kidneys, the ureter and the urinary bladder. To this end, the patient intravenously receives a small amount of contrast medium, which is excreted by the kidneys within just a few minutes. 10 to 20 minutes after administration of the contrast medium, x-ray images are produced to assess the excretion of the contrast medium by the kidneys. Depending on their composition, some stones are also directly visible in the x-ray image.

On the left: X-ray image showing a large stone in the renal pelvis
On the right: Contrast radiography of the left kidney with an engulfed renal pelvic stone

The prerequisite for performing excretory urography is a normal renal function. Since the contrast medium contains iodine, excretory urography is not possible in some thyroid diseases. This technique also cannot be used in pregnant women and where acute pain (renal colic) is present.

Computed tomography (CT)

Computed tomography is the most accurate method to diagnose kidney and ureteral stones. The patient is placed on a mobile imaging table and moved into the CT scanner, which produces cross-sectional images of the entire abdominal and pelvic area within just a few seconds.

In contrast to excretory urography, computed tomography does not require the administration of a contrast medium, which is why it can be used in most patients. However, a pregnancy constitutes a clear contraindication in this case as well.

Abdominal CT scan
On the right: Visualisation of kidneys in red, kidney stones in yellow, urinary bladder in green