| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Genitourinary Imaging |
1 From the Department of Radiology, University of Texas Health Science Center at Houston. Received October 1, 1998; revision requested November 11; revision received March 17, 1999; accepted April 8. Address reprint requests to I.C.B., Radiology Consultants, #350, 10655 Southport Rd SW, Calgary, Alberta, Canada T2W 4Y1 (e-mail: boridyl@aol.com).
 |
Abstract |
|---|
 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
MATERIALS AND METHODS: Nonenhanced helical CT and excretory urographic images in 82 patients with flank pain were retrospectively reviewed. For each patient, a radiologic diagnosis was established, and the degree of ureteral obstruction determined on urograms was compared with the extent of perinephric edema assessed on CT images.
RESULTS: None of 29 patients with no abnormalities seen at urography had evidence of perinephric edema at CT. Of six patients with noncalculous disease, two with acute pyelonephritis had perinephric edema at CT. Of 47 patients with acute ureterolithiasis, eight had no perinephric edema at CT and a nonobstructing calculus at urography, 21 had limited edema at CT and low-grade obstruction at urography, and 15 had extensive edema at CT and high-grade obstruction at urography. Three patients had extensive perinephric edema at CT but low-grade obstruction at urography. The extent of edema allowed accurate prediction of the degree of ureteral obstruction in 44 (94%) of 47 patients with acute ureterolithiasis.
CONCLUSION: The extent of perinephric edema on nonenhanced helical CT images can be used to predict the degree of ureteral obstruction in acute ureterolithiasis.
Index terms: Ureter, calculi, 82.811 • Ureter, CT, 82.12111, 82.12115 • Ureter, stenosis or obstruction, 82.811
|
Introduction |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
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 reactions. 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 (1–3). However, there has been concern among clinicians about the lack of physiologic information on nonenhanced CT scans; such information is available on urograms because of excretion of contrast material by the kidneys, including information about renal function and the degree of ureteral obstruction.
The purpose of this study was to determine whether this physiologic information can be derived from anatomic changes that are demonstrated at nonenhanced helical CT, by correlating the degree of ureteral obstruction with the extent of perinephric edema.
|
MATERIALS AND METHODS |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
Early in our experience with nonenhanced helical CT, a small group of urologists and emergency physicians at our institution had not yet fully accepted this technique and insisted on acquisition of an excretory urogram after CT regardless of the findings from the latter. Therefore, of the 216 patients evaluated with nonenhanced CT during that period, 82 patients also underwent excretory urography after CT, as requested by these physicians. These 82 patients (45 men, 37 women; mean age, 36 years; age range, 19–67 years) constituted the population of this study.
CT was performed with a HiSpeed Advantage CT system (GE Medical Systems, Milwaukee, Wis) by using helical data acquisition with 5-mm collimation, an incremental table speed of 8 mm/sec, a pitch of 1.6, 120 kVp, and at least 200 mA. The data were acquired from the top of the kidneys to the bottom of the bladder during two or three breath holds and without the use of intravenous or enteric contrast material. All images were displayed on hard copy at a soft-tissue window setting (window width, 450 HU; window level, 50 HU).
Excretory urography was performed immediately after CT, according to a routine protocol. After a scout radiograph of the abdomen and pelvis had been obtained, 100 mL of nonionic contrast material (iohexol, Omnipaque 300; Nycomed, Princeton, NJ) was injected intravenously by the supervising radiologist. One tomogram of the kidneys was obtained at 30 seconds after injection to document the nephrographic phase, and at least three tomograms of the kidneys were obtained at 7 minutes after injection to evaluate the parenchyma and the collecting system. Nontomographic views of the abdomen and pelvis were obtained at 5, 10, and 15 minutes after injection. If no obstruction was detected, the examination was completed with a postvoid radiograph of the bladder. If there was evidence of obstruction, additional delayed radiographs were obtained until the cause and level of the obstruction were demonstrated.
One author (C.M.S.) reviewed the paired CT and excretory urographic studies for each patient and established a radiologic diagnosis in each case. For each patient, the same author assigned a degree of ureteral obstruction, which was determined on the basis of the time needed at excretory urography to opacify the entire collecting system and ureter to the level of the calculus. A patient was classified as having no obstruction if there was no delay in excretion on the side of the calculus. A patient was classified as having a low-grade ureteral obstruction if full opacification of the collecting system and ureter to the location of the calculus was present within 15 minutes of injection of iohexol. A patient also was judged to have low-grade ureteral obstruction if the only sign of ureteral obstruction was a persistent column of contrast material in the ureter proximal to the calculus on several images, while the contralateral normal ureter drained satisfactorily. A patient was classified as having high-grade ureteral obstruction if full opacification to the location of the calculus was first visible later than 15 minutes after injection.
The nonenhanced helical CT scans in the 82 patients were reviewed jointly by two authors (I.C.B., A.K.) who were blinded to the radiologic assessment of their colleague and to the side of the symptoms. Nonenhanced CT scans were evaluated for the extent of perinephric edema. Patients were classified as having no perinephric edema, limited perinephric edema, or extensive perinephric edema, on the basis of an overall subjective assessment of the severity of three CT findings: (a) stranding of the perinephric fat manifesting as linear areas of soft-tissue attenuation parallel or perpendicular to the surface of the kidney; (b) perinephric fluid collection manifesting as discrete, more rounded areas of fluid attenuation in the perinephric space; and (c) thickening of the renal fascia manifesting as increased thickness of or fluid along the renal fascia (Figs 1–3). This assessment was determined by means of consensus by the two author-observers.
|
|
|
|
|
|
|
The thickness of the renal fascia was assessed in comparison with that of the fascia on the asymptomatic side. When the renal fascia on the symptomatic side was depicted as a clearly definable line in the background of perinephric and pararenal fat but was barely visible as a distinct structure on the asymptomatic side, the degree of fascial thickness was considered to be mild. When the renal fascia on the symptomatic side had a measurable thickness or when fluid was noted along or within the layers of the fascia, then the degree of fascial thickness was assessed as moderate to severe. For patients in whom changes were present in the perinephric space of both kidneys, the perinephric spaces were evaluated for symmetry. When the perinephric changes on the symptomatic side also were present to the same extent on the asymptomatic side, the patient was considered to have no perinephric edema. The changes in the perinephric space in these patients were not thought to result from acute ureteral obstruction related to ureterolithiasis, which should affect only the symptomatic side. When the changes in the perinephric space on the symptomatic side were more extensive than those on the asymptomatic side, the patient's condition was classified on the basis of the extent of perinephric edema on the side of the calculus, according to the criteria described earlier.
To determine the accuracy of nonenhanced helical CT for prediction of the degree of ureteral obstruction, the extent of perinephric edema was compared to the degree of ureteral obstruction as determined on excretory urograms in the 47 patients with ureterolithiasis. The 95% CIs were calculated for sensitivity, specificity, positive predictive value, and negative predictive value (4).
|
RESULTS |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
The 29 patients with no abnormality seen on imaging studies and the six with noncalculous disease showed no delay in excretion of contrast material on either side on excretory urograms. The eight patients with ureterolithiasis but no changes of perinephric edema on CT images showed no delay in excretion of contrast material on the side of the calculus on excretory urograms; that is, they had a nonobstructing calculus. All 21 patients with ureterolithiasis and limited perinephric edema on CT images had a low-grade ureteral obstruction on excretory urograms. Of the 18 patients with ureterolithiasis and extensive perinephric edema on CT images, 15 had a high-grade ureteral obstruction and three had a low-grade ureteral obstruction on excretory urograms (Table).
|
The finding of limited perinephric edema on CT images had a sensitivity of 88% (21 of 24; 95% CI = 0.70, 0.96), a specificity of 100% (23 of 23; 95% CI = 0.86, 1.00), a positive predictive value of 100% (21 of 21; 95% CI = 0.85, 1.00), and a negative predictive value of 88% (23 of 26; 95% CI = 0.72, 0.96) for prediction that a calculus was associated with a low-grade ureteral obstruction.
The finding of extensive perinephric edema on CT images had a sensitivity of 100% (15 of 15; 95% CI = 0.80, 1.00), a specificity of 91% (29 of 32; 95% CI = 0.76, 0.97), a positive predictive value of 83% (15 of 18; 95% CI = 0.60, 0.94), and a negative predictive value of 100% (29 of 29; 95% CI = 0.94, 1.00) for prediction of a high-grade ureteral obstruction. The extent of perinephric edema as seen on CT images allowed accurate prediction of the degree of ureteral obstruction in 44 (94%) of 47 patients (95% CI = 0.83, 0.98).
|
DISCUSSION |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
Clinicians are also interested in the severity of ureteral obstruction associated with a ureteral calculus, information that is readily available on excretory urograms. On urograms, the time needed to opacify the ureter to the point of the calculus is directly proportional to the degree of ureteral obstruction. Although CT helps accurately determine the size and location of ureteral calculi, it does not provide direct functional information related to excretion of contrast material. 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. 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 anatomic changes that occur in the perinephric space in the presence of ureterolithiasis are thought to result from the physiologic adaptations of a kidney subjected to acute obstruction. When acutely obstructed, the kidney responds to the increased pressure in the ureter with resorption of urine through several pathways, including pyelosinus, pyelotubular, pyelolymphatic, and pyelovenous backflow mechanisms (8). Perinephric edema probably represents resorbed urine infiltrating the perinephric space along the bridging septa described by Kunin (9). The presence of fluid in the perinephric space has also been observed in cases of acutely obstructed kidneys imaged with magnetic resonance urography (10).
The CT assessment of the extent of perinephric edema was accurate for prediction of the degree of ureteral obstruction in 44 (94%) of 47 patients. In two of the three patients in whom the degree of obstruction was inaccurately categorized on the basis of CT findings, the excretory urogram was performed more than 2 hours after CT, owing to unavoidable delays in the radiology department, and did not demonstrate the distal ureteral calculus, which was clearly depicted on the CT study. This raises the possibility that the calculus in these patients may have passed in the interval between imaging studies, possibly because the diuresis that resulted from intravenous administration of contrast material may have flushed the calculus into the bladder. This would explain why CT was predictive of a high-grade ureteral obstruction when the excretory urogram demonstrated only a mild delay in excretion and formation of a contrast material column to the level of the ureterovesical junction on the 15-minute upright urogram. Passage of a calculus was not recorded in the medical records of these patients; therefore, this explanation remains speculative.
In the third patient in whom the CT and excretory urographic findings were not correlated, there was no delay between performance of the studies, and the calculus was clearly identified on each study. In this patient, the excretory urogram demonstrated a low-grade ureteral obstruction, whereas the CT finding of extensive perinephric edema was predictive of a high-grade ureteral obstruction. Perhaps another mechanism, such as scarring from previous pyelonephritis, may be implicated for this discrepancy, although a corroborative history was not found in the medical records.
Another possible explanation for the discrepancy in these three patients is the phenomenon of forniceal rupture. In the setting of a substantial ureteral obstruction, a fornix may rupture and allow decompression of urine into the perinephric space in an attempt to lessen the pressure in the urinary tract. When such kidneys are imaged with CT, extensive changes of perinephric edema may be seen in the perinephric space, whereas the excretory urogram shows only a mild delay in excretion. This phenomenon represents a potential limitation of our study.
Of 43 patients without perinephric edema on CT images, 35 had no ureteral calculus and eight had a nonobstructing calculus. The findings indicate, therefore, that in the context of acute flank pain, the absence of perinephric edema is suggestive of either absence of a ureteral calculus or presence of a nonobstructing calculus. Of 39 patients with changes of perinephric edema on CT images, two had acute pyelonephritis, not acute ureterolithiasis. These results confirm findings from a previous report (9) that perinephric edema is a nonspecific finding that may be present in inflammatory or neoplastic diseases affecting the kidney, including, in particular, acute pyelonephritis.
Differentiation is easier when the clinical manifestation is known. The absence of a ureteral calculus or of dilatation of the collecting system and ureter and the presence of marked nephromegaly are features that support a diagnosis of inflammation rather than obstruction. In the occasional case where a calculus is associated with infection in the collecting system and ureter, interpretation of the importance of perinephric edema becomes more challenging. In such patients, repeat CT after intravenous administration of contrast material may help solve the problem.
In conclusion, our 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. Our results indicate that the extent of perinephric edema on nonenhanced helical CT images can be used to predict the degree of ureteral obstruction in most patients with acute ureterolithiasis. In the future, it would be interesting to use an animal model to correlate the extent of perinephric edema with the severity and chronicity of ureteral obstruction and to study the temporal changes in edema as the obstruction is relieved.
|
Footnotes |
|---|
Author contributions: Guarantor of integrity of entire study, I.C.B.; study concepts and design, I.C.B.; definition of intellectual content, I.C.B.; literature research, I.C.B., C.M.S.; clinical studies, I.C.B., A.K., C.M.S.; data acquisition and analysis, I.C.B.; statistical analysis, I.C.B.; manuscript preparation, I.C.B.; manuscript editing, I.C.B., A.K., C.M.S.; manuscript review, all authors.
|
References |
|---|
|
TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
Related Article
This article has been cited by other articles:
|
|
 |
|
  S J Freeman and H Sells Investigation of loin pain Imaging, March 1, 2008; 20(1): 38 - 56. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Memarsadeghi, C. Schaefer-Prokop, M. Prokop, T. H. Helbich, C. C. Seitz, I. M. Noebauer-Huhmann, and G. Heinz-Peer Unenhanced MDCT in Patients with Suspected Urinary Stone Disease: Do Coronal Reformations Improve Diagnostic Performance? Am. J. Roentgenol., August 1, 2007; 189(2): W60 - W64. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S J Freeman and H Sells Investigation of loin pain Imaging, August 1, 2005; 17(1): 19 - 33. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Memarsadeghi, G. Heinz-Peer, T. H. Helbich, C. Schaefer-Prokop, G. Kramer, M. Scharitzer, and M. Prokop Unenhanced Multi-Detector Row CT in Patients Suspected of Having Urinary Stone Disease: Effect of Section Width on Diagnosis Radiology, May 1, 2005; 235(2): 530 - 536. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. P. Tamm, P. M. Silverman, and W. P. Shuman Evaluation of the Patient with Flank Pain and Possible Ureteral Calculus Radiology, August 1, 2003; 228(2): 319 - 329. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
O. Catalano, A. Nunziata, F. Altei, and A. Siani Suspected Ureteral Colic: Primary Helical CT Versus Selective Helical CT After Unenhanced Radiography and Sonography Am. J. Roentgenol., February 1, 2002; 178(2): 379 - 387. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. C. Smith and M. Varanelli Diagnosis and Management of Acute Ureterolithiasis: CT Is Truth Am. J. Roentgenol., July 1, 2000; 175(1): 3 - 6. [Full Text] [PDF]
|
|
|
|
|
|
E. S. Amis Jr Epitaph for the Urogram Radiology, December 1, 1999; 213(3): 639 - 640. [Full Text]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| RADIOLOGY | RADIOGRAPHICS | RSNA JOURNALS ONLINE |
