Stones in renal parenchyma or collecting system

Stones (calculi) contain varying amounts of calcium. The higher the calcium content, the better they can be seen on X-ray. Stones can be detected with plain X-ray, but it is not possible to determine the precise location of the stone with this technique, or if it is obstructing part of the renal pelvis or urinary tract further downstream (ureter).

Urography, which is a X-ray examination with injection of an iv contrast medium, is still the most widely used examination. Urography gives a detailed visualisation of the renal calyces, pelvis, ureter and urinary bladder, because the injected contrast medium is excreted by the kidneys into the collecting system after just a few minutes. A calculi (or any other space-occupying lesion for that matter), will show up as a kind of a filling defect. Urography can rule out obstruction or assess degree of obstruction, which is a very important issue to recognise when treating the patient.

CT without contrast media is increasingly used to detect smaller stones with less calcium not visualised otherwise.

Ultrasound can detect stones above about 3-4 mm in the kidneys or pelvis, but is, for practical purposes, insensitive regarding to stones more downstream. On the other hand, ultrasound can, in most cases, rule out any significant obstruction resulting in distension of the collecting system. Persistent obstruction will in time damage the kidney function on the side in question. This can be monitored by NM split function studies.