Detection of ureteral calculi in patients with suspected renal colic: value of reformatted noncontrast helical CT.

OBJECTIVE

The purpose of this study was to determine the value of reformatted noncontrast helical CT in patients with suspected renal colic. We hoped to determine whether this technique might create images acceptable to both radiologists and clinicians and replace our current protocol of sonography and abdominal plain film.

SUBJECTS AND METHODS

Thirty-four consecutive patients with signs and symptoms of renal colic were imaged with both noncontrast helical CT and a combination of plain film of the abdomen and renal sonography. Reformatting of the helical CT data was performed on a workstation to create a variety of reformatted displays. The correlative studies were interpreted by separate blinded observers. Clinical data, including the presence of hematuria and the documentation of stone passage or removal, were recorded.

RESULTS

Findings on 18 CT examinations were interpreted as positive for the presence of ureteral calculi; 16 of these cases were determined to be true positives on the basis of later-documented passage of a calculus. Thirteen of the 16 cases proved to be positive were interpreted as positive for renal calculi using the combination of abdominal plain film and renal sonography. The most useful CT reformatting technique was curved planar reformatting of the ureters to determine whether a ureteral calculus was present.

CONCLUSION

In this study, noncontrast helical CT was a rapid and accurate method for determining the presence of ureteral calculi causing renal colic. The reformatted views produced images similar in appearance to excretory urograms, aiding greatly in communicating with clinicians. Limitations on the technique include the time and equipment necessary for reformatting and the suboptimal quality of reformatted images when little retroperitoneal fat is present.