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Is spiral computed tomography the imaging modality of choice for renal colic?

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Q1: What is the diagnosis, and what is spiral computed tomography?

The patient was diagnosed as having left sided renal colic due to a calculus in her left proximal ureter. A spiral computed tomogram allows imaging of the entire abdomen and pelvis during one breath hold, eliminating respiratory artefacts. The entire technique of performing spiral computed tomography takes approximately 30 seconds to complete.

Q2: What are the findings on the spiral computed tomogram?

A spiral computed tomogram of the abdomen was performed. No intravenous contrast medium was used during the procedure. It showed a normal right renal tract. There was a 6 mm calculus in the proximal left ureter and an 8 mm calculus in the inferior pole calyx of the left kidney (fig 1; see p 124). These calculi were not visualised in the intravenous urogram.

Q3: What are the advantages of spiral computed tomography in evaluating a case of renal colic?

There are several advantages in performing a spiral computed tomogram to evaluate acute flank pain. As the imaging with spiral computed tomography is performed without contrast medium, the stones are not masked by the presence of radio-opaque contrast. With conventional computed tomography stepwise slices are taken and therefore it is possible to miss a stone. Spiral computed tomography provides a continuum profile of the urinary tract and therefore is unlikely to miss a stone. Like an intravenous urogram but unlike an ultrasound scan, a spiral computed tomogram gives good imaging of the ureter and has the same advantage as an intravenous urogram to be able to delineate the level of obstruction. Unenhanced spiral computed tomography is reported to have more than 95% sensitivity and specificity in the diagnosis of obstructing ureteral calculi. Within the next few years spiral computed tomography may replace intravenous urography in the evaluation of renal colic.

Discussion

Intravenous urography has been the procedure of choice for evaluation of renal colic since it was first performed in 1923.1 It provides structural as well as functional information of the urinary tract. In addition it gives us information regarding the site, degree, and the nature of obstruction. There are a few disadvantages with intravenous urography. The incidence of contrast induced allergic reactions is 5%–10%.2 3 There is 25% risk of contrast induced nephrotoxicity in people with pre-existing renal failure and diabetes mellitus.4 Intravenous urography is more time consuming. On the other hand spiral computed tomography has several advantages. As the imaging with spiral computed tomography is performed without contrast medium, the stones are not masked by the presence of radio-opaque contrast. Total time taken to perform a spiral computed tomography is less than a minute. Like an intravenous urogram, but unlike an ultrasound scan, a spiral computed tomogram gives good imaging of the ureter and has the same advantage as an intravenous urogram to be able to delineate the level of obstruction. The sensitivity and specificity of unenhanced spiral computed tomography in the diagnosis of renal colic is reported to be more than 95%.5-7 Evaluation of spiral computed tomography and intravenous urography revealed comparable radiation dosages and with a lower gonadal dose provided by the spiral computed tomography.8 The main disadvantage of unenhanced spiral computed tomography compared with intravenous urography is the absence of evaluation of renal function and the lining epithelium of the urinary tract. Rarely phleboliths in the pelvis could be confused with ureteral stones on spiral computed tomography.

Learning points: advantages of spiral computed tomography

  • No bowel preparation or contrast medium is required

  • It requires less time than intravenous urography. Entire technique of spiral computed tomography takes approximately 30 seconds

  • It scans the entire abdomen and pelvis during one breath hold, eliminating respiratory artefacts

  • It is highly accurate in identifying the size and location of ureteral and renal calculi

  • Uric acid calculi could be accurately diagnosed

  • The degree of obstruction to the kidney can be assessed by the severity of hydronephrosis, perinephric, and periureteral stranding and perinephric fluid collection indicating forniceal rupture

  • In addition other abdominal organs can be evaluated

  • Radiation dosage is comparable to that of intravenous urography (4.6 v 4.4 rad, respectively), with a lower gonadal dose provided by the spiral computed tomography

References

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