URETERIC STONES RADIOLOGICAL IMAGING

Ureteric stones: diagnostic radiological imaging
The intravenous urogram (IVU), for many years the mainstay of imaging in patients with flank pain, has been replaced by CT urography (CTU). Compared with IVU, CTU:
- Has greater specificity (95%) and sensitivity (97%) for diagnosing ureteric stones it can identify other, non-stone causes of flank pain.
- Requires no contrast administration so avoiding the chance of a contrast reaction (risk of fatal anaphylaxis following the administration of low-osmolality contrast media for IVU is in the order of 1 in 100,000).
- Is faster, taking just a few minutes to image the kidneys and ureters. An IVU, particularly where delayed films are required to identify a stone causing high-grade obstruction, may take hours to identify the precise location of the obstructing stone.
- Is equivalent in cost to IVU, in hospitals where high volumes of CT scans are done.

If you only have access to IVU, remember that it is contraindicated in patients with a history of previous contrast reactions and should be avoided in those with hay fever, a strong history of allergies, or asthma who have not been pre-treated with high-dose steroids 24h before the IVU. Patients taking metformin for diabetes should stop this for 48h prior to an IVU. Clearly, being able to perform an alternative test, such as CTU in such patients, is very useful.

Where 24-h CTU access is not available, admit patients with suspected ureteric colic for pain relief and arrange a CTU the following morning. When CT urography is not immediately available (between the hours of midnight and 8 a.m.) we arrange urgent abdominal ultrasonography in all patients aged >50 years who present with flank pain suggestive of a possible stone, to exclude serious pathology such as a leaking abdominal aortic aneurysm and to demonstrate any other gross abnormalities due to non-stone associated flank pain.
Plain abdominal X-ray and renal ultrasound are not sufficiently sensitive or specific for their routine use for diagnosing ureteric stones.

MR urography
This a very accurate way of determining whether a stone is present in the ureter or not. However, at the present time, cost and restricted availability limit its usefulness as a routine diagnostic method of imaging in cases of acute flank pain. This may change as MR scanners become more widely available.