In this issue of Radiology, Dr. E. Stephen Amis, Jr., from the Albert Einstein College of Medicine notes that one reason why use of the excretory urogram continues today is because nonenhanced CT was failing to show the degree of obstruction caused by urinary tract calculi. But this limitation is addressed a few pages later by Dr. Illya Boridy and colleagues from the University of Texas Health Science Center at Houston.
There are a number of reasons why nonenhanced CT is preferable to the urogram, according to Boridy et al.
"Nonenhanced CT can be completed promptly and does not necessitate the use of an intravenously administered contrast agent, which has associated costs and the risk of adverse reaction," they write. "In addition, CT is more sensitive than excretory urography for demonstrating ureteral calculi, in particular nonopaque calculi and calculi at the ureterovesical junction, and may demonstrate extraurinary causes of ureteral obstruction or other abdominal and pelvic pathologic conditions."
Determining the size and location of the calculus is important in management of patients with acute ureterolithiasis because size and location "can help predict which calculi will pass spontaneously," the authors note. Clinicians also want to know the severity of ureteral obstruction associated with a ureteral calculus, information that is readily available on excretory urograms but not on nonenhanced CT.
"The purpose of this study was to determine whether this physiologic information could be derived from the anatomic changes that occur in the perinephric space in the presence of ureterolithiasis," the authors write.
"Our findings indicate that the extent of perinephric edema on the side of the ureteral calculus (defined as the presence of strands of soft-tissue attenuation in the perinephric fat, perinephric fluid collections, and thickening of or fluid along the renal fascia) was directly proportional to the degree of ureteral obstruction."
The researchers retrospectively reviewed nonenhanced spiral CT and excretory urograms from 82 patients with flank pain. In each case the degree of ureteral obstruction determined by the urograms was compared with the extent of perinephric edema seen on CT.
There was no evidence of perinephric edema for any of the 29 patients with normal urograms. Of the six patients with noncalculous disease, perinephric edema was seen on the two with acute pyelonephritis. And in the remaining 47 patients with acute ureterolithiasis, extent of edema allowed accurate prediction of the degree of ureteral obstruction in 44, or 94%, of cases, the authors write.
"(O)ur results demonstrate how the physiologic information that is obtained at excretory urography performed with iodinated contrast material can be derived at nonenhanced helical CT by carefully analyzing the anatomic alterations that occur in the perinephric space in the setting of acute ureteral obstruction," the authors conclude.
There are a number of reasons why nonenhanced CT is preferable to the urogram, according to Boridy et al.
"Nonenhanced CT can be completed promptly and does not necessitate the use of an intravenously administered contrast agent, which has associated costs and the risk of adverse reaction," they write. "In addition, CT is more sensitive than excretory urography for demonstrating ureteral calculi, in particular nonopaque calculi and calculi at the ureterovesical junction, and may demonstrate extraurinary causes of ureteral obstruction or other abdominal and pelvic pathologic conditions."
Determining the size and location of the calculus is important in management of patients with acute ureterolithiasis because size and location "can help predict which calculi will pass spontaneously," the authors note. Clinicians also want to know the severity of ureteral obstruction associated with a ureteral calculus, information that is readily available on excretory urograms but not on nonenhanced CT.
"The purpose of this study was to determine whether this physiologic information could be derived from the anatomic changes that occur in the perinephric space in the presence of ureterolithiasis," the authors write.
"Our findings indicate that the extent of perinephric edema on the side of the ureteral calculus (defined as the presence of strands of soft-tissue attenuation in the perinephric fat, perinephric fluid collections, and thickening of or fluid along the renal fascia) was directly proportional to the degree of ureteral obstruction."
The researchers retrospectively reviewed nonenhanced spiral CT and excretory urograms from 82 patients with flank pain. In each case the degree of ureteral obstruction determined by the urograms was compared with the extent of perinephric edema seen on CT.
There was no evidence of perinephric edema for any of the 29 patients with normal urograms. Of the six patients with noncalculous disease, perinephric edema was seen on the two with acute pyelonephritis. And in the remaining 47 patients with acute ureterolithiasis, extent of edema allowed accurate prediction of the degree of ureteral obstruction in 44, or 94%, of cases, the authors write.
"(O)ur results demonstrate how the physiologic information that is obtained at excretory urography performed with iodinated contrast material can be derived at nonenhanced helical CT by carefully analyzing the anatomic alterations that occur in the perinephric space in the setting of acute ureteral obstruction," the authors conclude.
