388 CHAPTER 8 Stone disease

Ureteric stones: diagnostic radiological imaging

The intravenous pyelogram (IVP), for many years the mainstay of imaging in patients with flank pain, has been replaced by CT urography (CTU) (Fig. 8.11). Compared with IVP, CTU

-Has greater specificity (95%) and sensitivity (97%) for diagnosing ureteric stones1—it can identify other, non-stone causes of flank pain (Fig. 8.12).

-Requires no contrast administration, avoiding the chance of a contrast reaction (risk of fatal anaphylaxis following the administration of lowosmolality contrast media for IVP is on the order of 1 in 100,000).2

-Is faster, taking just a few minutes to image the kidneys and ureters. An IVP, particularly when 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 that of IVP, in hospitals where high volumes of CT scans are done.3

If you only have access to IVP, 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 pretreated with high-dose steroids 24 hours before the IVP. Patients taking metformin for diabetes should stop this for 48 hours prior to an IVP. Clearly, being able to perform an alternative test, such as CTU in such patients, is very useful.

Where 24-hour CTU access is not available, admit patients with suspected ureteric colic for pain relief and arrange for a CTU the following morning. When CT urography is not immediately available (between the hours of midnight and 8 a.m.), we obtain 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

MRU is a very accurate way of determining whether a stone is present in the ureter or not.4 However, cost and restricted availability limit its usefulness as a routine diagnostic method of imaging in cases of acute flank pain. This situation may change as MR scanners become more widely available.

1 Smith RC, Verga M, McCarthy S, Rosenfield AT (1996). Diagnosis of acute flank pain: value of unenhanced helical CT. Am J Roentgen 166:97–101.

2 Caro JJ, Trindale E, McGregor M (1991). The risks of death and severe non-fatal reactions with high vs low osmolality contrast media. Am J Roentgen 156:825–832.

3 Thomson JM, Glocer J, Abbott C, et al. (2001) Computed tomography versus intravenous urography in diagnosis of acute flank pain from urolithiasis: a randomized study comparing imaging costs and radiation dose. Australas Radiol 45:291–297.

4 Louca G, Liberopoulos K, Fidas A, et al. (1999) MR urography in the diagnosis of urinary tract obstruction. Eur Urol 35:102–108.

URETERIC STONES: DIAGNOSTIC RADIOLOGICAL IMAGING 389

Figure 8.11 CT urogram.

Figure 8.12 A leaking aortic aneurysm identified on a CTU in a patient with flank pain.

390 CHAPTER 8 Stone disease

Ureteric stones: acute management

While appropriate imaging studies are being organized, pain relief should be given.

-A nonsteroidal anti-inflammatory (NSAID) (e.g., diclofenac—Voltaren or ketorolac tromethamine—Toradol) by intramuscular or intravenous injection, by mouth or per rectum, provides rapid and effective pain control. Its analgesic effect is partly anti-inflammatory, partly by reducing ureteric peristalsis.

-When NSAIDs are inadequate, opiate analgesics such as dilaudid or morphine are added.

-Calcium channel antagonists (e.g., nifedipine) may reduce the pain of ureteric colic by reducing the frequency of ureteric contractions.1,2 This is used for upper ureteral stones, whereas A-blockers (e.g., Flomax and Uroxatral) may be used for distal ureteral stones.

There is no need to encourage the patient to drink copious amounts of fluids or to give them large volumes of fluids intravenously in the hope that this will flush out the stone. Renal blood flow and urine output from the affected kidney fall during an episode of acute, partial obstruction due to a stone.

Excess urine output will tend to cause a greater degree of hydronephrosis in the affected kidney, which will make ureteric peristalsis even less efficient than it already is. Peristalsis, the forward propulsion of a bolus of urine down the ureter, can only occur if the walls of the ureter above the bolus of urine can coapt, i.e., close firmly together. If they cannot, as occurs in a ureter distended with urine, the bolus of urine cannot move distally.

Watchful waiting

In many instances, small ureteric stones will pass spontaneously within days or a few weeks, with analgesic supplements for exacerbations of pain.

Chances of spontaneous stone passage depend principally on stone size. Between 90% and 98% of stones measuring <4 mm will pass spontaneously.3,4 Average time for spontaneous stone passage for stones 4–6 mm in diameter is 3 weeks.

Stones that have not passed in 2 months are unlikely to do so. Therefore, accurate determination of stone size (on plain abdominal X-ray or by CTU) helps predict chances of spontaneous stone passage.

1 B Borghi L, et al. (1994). Nifedipine and methylprednisolone in facilitating ureteral stone passage: a randomised, double-blind, placebo controlled study. J Urol 152:1095–1098.

2 Porpiglia F, et al. (2000). Effectiveness of nifedipine and deflazacort in the management of distal ureteric stones. Urology 56:579–582.

3 Segura JW, et al. (1997). Ureteral stones guidelines panel summary report on the management of ureteral calculi. J Urol 158:1915–1921.

4 Miller OF, et al. (1999). Time to stone passage for observed ureteral calculi. J Urol 162:688–691.