NONCONTRAST HELICAL CT FOR URETERAL STONES

Noncontrast helical computed tomography (CT) has recently been found t o be superior to excretory urography (IVU) in the evaluation of patien ts with suspected ureterolithiasis. Noncontrast helical CT does not re quire the use of intravenous contrast material with its associated cos t and risk of adverse reactions and can be completed within 5 min, in most cases. Noncontrast CT often detects extraurinary pathology respon sible for the patient's symptoms. CT is also more sensitive than IVU i n detecting the calculus, regardless of its size, location, and chemic al composition. However, confidently differentiating ureteral calculi from phleboliths along the course of the ureter may, at limes, be diff icult. The ''tissue-rim'' sign, a rim of soft tissue attenuation aroun d the suspicious calcification, is helpful in making this distinction. Noncontrast CT does not provide physiological information about renal function and the degree of obstruction. A pilot study has suggested a proportional relationship between the extent of perinephric edema and the degree of obstruction. The cost of the examination and the radiat ion dose delivered to the patient may be higher with CT. Despite these limitations, noncontrast helical CT has quickly become the imaging st udy of choice in evaluating patients with acute flank pain.