Investigation of Suspected Ureteric Colic
The intravenous urogram (IVU) was for many years the mainstay of diagnostic imaging in patients with flank pain (Fig. 3.1). The last few years have seen a move toward computed tomography (CT) urography (CTU) (Fig. 3.2). CTU has the following advantages over IVU:
FIGURE 3.1. a: An intravenous urogram (IVU) control film. Two calcifications are seen in the left hemipelvis. Which is the ureteric stone? b: Following contrast administration, the lateral calcification is seen to lie outside the ureter; it is a phlebolith. The medial calcification is a ureteric stone.
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FIGURE 3.1. Continued
22 J. REYNARD
FIGURE 3.2. A computed tomography (CT) urogram (CTU). Stones 'light' up as very radiodense structures. There is one in the left ureter and one in the right kidney.
1. It has greater specificity (95%) and sensitivity (97%) for diagnosing ureteric stones than has IVU (Smith et al. 1996). CTU can identify other, non-stone causes of flank pain such as leaking aortic aneurysms (Fig. 3.3).
2. There is no need for contrast administration with CTU. This avoids the chance of a contrast reaction. The risk of fatal anaphylaxis following the administration of low-osmolality contrast media for IVU is on the order of 1 in 100,000 (Caro et al. 1991).
3. CTU is faster, taking just a few minutes to image the kidneys and ureters. An IVU, particularly where delayed ilms are required to identify a stone causing high-grade obstruction, may take hours to identify the precise location of the obstructing stone (Fig. 3.4).
4. In some hospitals, where high volumes of CT scans are done, the cost of CTU is equivalent to that of IVU (Thomson et al. 2001).
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FIGURE 3.3. A leaking abdominal aortic aneurysm, referred as a ureteric stone, but correctly diagnosed by CTU.
If you only have access to IVU, remember that it is contraindi-cated in patients with a history of previous contrast reactions, and should be avoided in those with hay fever or a strong history of allergies or asthma who have not been pretreated with highdose steroids 24 hour before the IVU. Patients taking metformin for diabetes should stop this for 48 hours prior to an IVU. Clearly, being able to perform an alternative test in such patients, such as CTU, is very useful.