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PROSPECTIVE COMPARISON OF NONENHANCED HELICAL COMPUTERIZED TOMOGRAPHY AND DOPPLER ULTRASONOGRAPHY FOR THE DIAGNOSIS OF RENAL COLIC
0022-5347/01/1654-1082/0 THE JOURNAL OF UROLOGY® Copyright © 2001 by AMERICAN UROLOGICAL ASSOCIATION, INC.®
Vol. 165, 1082–1084, April 2001 Printed in U.S.A.
PROSPECTIVE COMPARISON OF NONENHANCED HELICAL COMPUTERIZED TOMOGRAPHY AND DOPPLER ULTRASONOGRAPHY FOR THE DIAGNOSIS OF RENAL COLIC AHMED A. SHOKEIR
AND
MAGDY ABDULMAABOUD
From the Urology and Nephrology Center and Radiology Department, Mansoura University, Mansoura, Egypt
ABSTRACT
Purpose: We evaluate the accuracy of nonenhanced helical computerized tomography (CT) and Doppler ultrasonography for the diagnosis of renal colic. Materials and Methods: Our study includes 109 patients, with 218 kidneys, who presented with unilateral flank pain. All patients underwent nonenhanced helical CT, Doppler ultrasonography and excretory urography (IVP). CT was evaluated for the presence of ureteral stones and manifestation of ureteral obstruction. For Doppler ultrasonography the renal resistive index was measured for the left and right kidneys in each patient, and change in resistive index between ipsilateral and contralateral kidneys was calculated and considered positive for ureteral obstruction with values 0.04 or greater. As a reference standard, absence of obstruction was considered if IVP was negative and the cause of flank pain was confirmed not to be urological. Obstruction was diagnosed not only by positive IVP, but also by patient followup until passage or retrieval of ureteral stones. Results of CT and change in resistive index were compared with those of the reference standard. Results: Unilateral ureteral obstruction was confirmed in 52 patients, while no obstruction was found in 57. Of the 57 patients without ureterolithiasis the change in resistive index results was negative in all patients with a specificity of 100%, while CT was negative in 55 with a specificity of 96%. Of the 52 patients with ureteral obstruction CT was positive in 50, and change in resistive index was positive in 47 with a sensitivity of 96% and 90%, respectively, with a difference of no significant value. Conclusions: Nonenhanced helical CT and change in resistive index are sensitive and specific tests that can contribute significantly to the diagnosis of acute unilateral renal obstruction. They can replace IVP, particularly in situations in which it is undesirable. KEY WORDS: kidney; ureter; ureteral obstruction; colic; tomography, x-ray computed
Acute renal colic is one of the most anguishing forms of pain in humans that needs quick diagnosis and treatment. The magnitude of the problem is large worldwide, and the lifetime risk of an attack of acute renal colic is estimated at 1% to 10%.1 It is caused by acute partial ureteral obstruction due to a calculus in the vast majority of cases. Traditionally, besides routine clinical examination, acute renal colic has been diagnosed with routine plain film of the kidneys, ureters and bladder, conventional gray-scale ultrasonography and excretory urography (IVP). During the last few years, the introduction of noncontrast computerized tomography (CT) and Doppler ultrasonography has changed the strategy of diagnosis of renal colic. We evaluate the diagnostic accuracy of the recent nonenhanced helical CT and Doppler ultrasonography for renal colic. MATERIALS AND METHODS
Between March and October 1999 each patient presenting with acute unilateral flank pain at the emergency department or urology clinic of New Jeddah Clinic Hospital was enrolled in the study. Patients were excluded from study if they presented with serum creatinine greater than 2 mg./dl., pregnancy, allergy to radiocontrast, bilateral flank pain or a
solitary kidney. A total of 170 patients were eligible and 125 agreed to participate. After informed consent all patients underwent nonenhanced helical CT, Doppler ultrasonography and then IVP. Radiography was performed before giving medications in most and during an attack of loin pain in all patients. Patients diagnosed as having ureteral stones were followed until passage or retrieval of stones. Nonenhanced helical CT was performed with a Sytec SRI* scanner. No oral or intravenous contrast material was used. Spiral scans were performed from the top of the kidney to the bladder base with the table feed rate at 5 mm. per rotation and a nominal section thickness of 5 mm. (pitch ⫽ 1). Image reconstruction was routinely performed at 5 mm. increments with 360 degree interpolation. When calcific density was seen along the course of the ureter, further evaluation of this region was performed with retrospective reconstruction in 2 mm. increments. In some patients reformatted images were also obtained with overlapped sections in 2 mm. intervals to create images similar to IVP. CT was considered diagnostic of ureterolithiasis if a calculus was seen in the ureter with or without secondary signs of obstruction, including ureteral or renal dilatation, soft tissue ring sign, loss of renal pelvic fat planes or perinephric stranding. A stone obstructing the right pelviureteral junction and causing dilation of the renal pelvis is shown in figure 1, A. The ring sign denotes visualization of a rim of soft tissue surrounding a stone (fig. 1, B). This sign represents the edematous wall of the ureter and is helpful in distinguishing stones from phleboliths (fig. 1, C).
Accepted for publication October 6, 2000. Editor’s Note: This article is the first of 5 published in this issue for which category 1 CME credits can be earned. Instructions for obtaining credits are given with the questions on pages 1264 and 1265. *General Electric, Milwaukee, Wisconsin. 1082
1083
COMPUTERIZED TOMOGRAPHY VERSUS ULTRASONOGRAPHY FOR RENAL COLIC
FIG. 1. Nonenhanced helical CT of stone at right (R) pelviureteral junction (arrow) with secondary dilatation of renal pelvis (A), of stone in pelvic part of left (L) ureter with soft tissue ring sign (arrow) (B) and of right pelvic phlebolith (arrow) simulating ureteral stone but without ring sign (C).
Doppler ultrasonography was performed using an SSD2000† multiview unit with a transducer frequency of 3.5 MHz. At least 5 Doppler spectra were obtained from more than 3 regions in each kidney. Doppler signals were obtained from arcuate arteries at the corticomedullary junctions, interlobar arteries along the border of the medullary pyramids or both. The Doppler waveforms were made using the lowest pulse repetition frequency possible without aliasing. This procedure maximized the size of the Doppler spectrum and decreased the percentage error in the measurements. In addition, the lowest possible wall filter for each ultrasound scanner was used. The Doppler sample width was set at 2 to 5 mm. The renal resistive index was calculated as peak systolic velocity-end diastolic velocity/peak systolic velocity, with change in resistive index determined as the change in resistive index of the corresponding and contralateral kidneys. Values of and change in resistive index used for statistical analysis were totaled by mean measurements in individual patients. Doppler ultrasonography was considered positive for obstruction if change in resistive index was 0.04 or greater.2 Doppler ultrasonography of a patient with left renal colic is shown in figure 2. IVP was performed in standard fashion with 50 to 100 cc iopromide nonionic contrast, and was interpreted as negative with a nonequivocal normal reno-ureteral unit and as positive with hydroureter proximal to a ureteral stone with delayed pelvicaliceal filling with contrast medium. As a reference standard, absence of obstruction was considered if IVP was negative and the cause of flank pain was confirmed not to be urological. Obstruction was diagnosed not only by positive IVP, but also by patient followup until passage or retrieval of ureteral stones. The sensitivity, specificity and overall accuracy of CT and change in resistive index for the diagnosis of acute unilateral ureteral obstruction were calculated. Differences were assessed using the chi-square and student t tests, as appropriate. †Aloka, Tokyo, Japan.
RESULTS
Of the 125 patients who agreed to participate in the study 10 were lost to followup and 6 had equivocal or suboptimal IVP results. The study group included 109 patients with 218 kidneys. There were 77 males and 32 females with a total mean age of 39 years (range 19 to 61). Flank pain affected the right side in 69 and the left side in 40 patients. No ureteral obstruction was found in 57 patients. IVP showed that the left and right kidneys were normal and the cause of loin pain was confirmed not to be urological, including radiculitis in 10 patients, myositis in 14, appendicitis in 7, colitis in 9 and biliary colic in 17. Obstruction was diagnosed in 52 patients, and IVP showed nonequivocal evidence of unilateral ureteral obstruction with a normal contralateral kidney. Moreover, ureteral obstruction was confirmed by patient followup, including 40 who noticed spontaneous passage of stones during medical treatment and the remaining 12 underwent ureteroscopy with stone extraction. Of the 57 patients without ureterolithiasis CT was negative in all but 2 in whom pelvic phleboliths were interpreted as ureteral stones. In 7 patients there were calcifications that were not ureteral calculi, including pelvic phleboliths in 2, nonobstructing renal calculi in 2, calcified ovarian mass in 1, calcified uterine mass in 1 and calcified mesenteric lymph nodes in 1. Of the 52 patients with ureteral calculi CT documented stones with 1 or more of the secondary signs of obstruction in 50. In the remaining 2 patients with ureteral stones CT showed no evidence of calculus or obstruction. The agreement between CT results and those of the reference standard is given in the table. CT showed a sensitivity of 96%, a specificity of 96% and an overall accuracy of 96%. Mean resistive index plus or minus standard deviation was 0.685 ⫾ 0.03 in the 52 obstructed kidneys, significantly higher than that of 0.616 ⫾ 0.04 in the 166 normal kidneys (p ⬍0.001). Mean change in resistive index of patients with acute unilateral ureteral obstruction was significantly higher than that of those in whom the left and right kidneys were normal, at 0.059 ⫾ 0.01 and 0.005 ⫾ 0.003, respectively (p ⬍0.0001). The agreement between change in resistive index and the reference standard results for the diagnosis of acute unilateral ureteral obstruction is given in the table. Change in resistive index was sensitive in 90%, specific in
Agreement between nonenhanced helical CT and change in resistive index versus the reference standard for the diagnosis of acute unilateral ureteral obstruction in 109 patients Predicted Results
FIG. 2. Doppler ultrasonography of patient with left (L) renal colic. Resistive index (RI) is 0.72 for obstructed left kidney (A) and 0.63 for normal right (R) kidney (B). Change in resistive index between left and right kidneys is 0.09.
CT: Pos. Neg. Change in resistive index: Pos. Neg.
Reference Standard No. Pos.
No. Neg.
50 2
2 55
47 5
0 57
1084
COMPUTERIZED TOMOGRAPHY VERSUS ULTRASONOGRAPHY FOR RENAL COLIC
100% and accurate in 95% of patients. Comparison between these results and those of CT showed no significant difference. DISCUSSION
To our knowledge Smith et al were the first to advocate the use of noncontrast CT for the diagnosis of acute renal colic.3 Our present series has confirmed several recent studies that noncontrast CT is an accurate radiographic modality for evaluation of renal colic.4 – 8 The potential benefit of noncontrast CT is the use of it in patients with contrast allergies, those with preexisting renal failure and those with an unclear clinical diagnosis mimicking renal colic. In addition, CT can visualize all stones regardless of composition. The procedure takes only 5 minutes and at some health systems it has been estimated to cost no more than IVP. Besides stone visualization, several secondary CT signs of ureteral obstruction are often present and useful when a stone is not readily identified. In our series nonenhanced helical CT was sensitive in 96% and specific in 96% of patients diagnosed with renal colic. Moreover, CT identified other urinary and nonurinary abnormalities in 7 patients and directed further imaging and treatment. There are a number of potential pitfalls in the interpretation of CT. Phleboliths in the pelvis can often be seen along the normal anatomical course of the ureter and can mimic ureteral stones. The ring sign is helpful for distinguishing stones from phleboliths. A gonadal vein can sometimes be confused with a dilated ureter and can be distinguished by following the superior course of the structure in question. The main disadvantage of noncontrast CT compared to IVP is the absence of renal function evaluation. Moreover, radiation exposure of CT is generally higher, limiting use during pregnancy. In addition, CT services are not universally available, particularly for a 24-hour period, and a radiologist is required for the accurate interpretation of the films. Results of our present series have confirmed the recent observation that Doppler ultrasonography is a sensitive and specific method for the diagnosis of renal colic.2, 9 –11 The noninvasive nature of Doppler ultrasonography gives it a considerable appeal in potential application, particularly in situations in which IVP is not recommended, such as renal impairment and pregnancy. We have shown that change in resistive index is more useful for the diagnosis of acute renal colic than a solid value of resistive index, and that a change in resistive index 0.04 or greater gives the highest sensitivity and specificity.2 Nevertheless, in patients with solitary kidneys or those with bilateral renal obstruction, albeit clinically uncommon, change in resistive index is of no value. The diagnostic accuracy of this index may be decreased if the patients were given nonsteroidal anti-inflammatory drugs.12 Therefore, to achieve the highest diagnostic accuracy we recommend that Doppler ultrasonography, which is operator dependent and requires special experience, be performed before giving nonsteroidal anti-inflammatory drugs and during an attack of pain. The diagnostic approach of acute flank pain is controversial and can vary from center to center, city to city or country to country depending on what is considered acceptable. Important factors include the local prevalence of stone disease, medical resources available, relative costs in a particular system, and the merits and limitations of each diagnostic modality. However, there is an increasing trend towards noninvasive or minimally invasive procedures. Many cases
could be diagnosed with initial screening by clinical examination, plain film of kidneys, ureters and bladder, and conventional ultrasonography. Noninvasive Doppler ultrasonography, with a change in resistive index of 0.04 as the dividing line between obstruction and no obstruction, is helpful for equivocal cases. Noncontrast CT is a sensitive and specific test. However, because of some limitations it is our opinion that it be reserved for patients in whom plain film of kidneys, ureters and bladder, and ultrasonography with Doppler assistance could not complete the diagnosis. IVP is used for diagnosis in a few patients in whom other noninvasive procedures are indeterminate. Nevertheless, IVP is indispensable if interventional treatment is planned. A noteworthy observation is that approximately 5% of patients were excluded from the study because of equivocal or suboptimal IVP results. Since IVP was part of the reference standard, a bias could have been introduced into the study. Another potential source of bias is that the interpreters of the study were not blinded to the results of the competing modalities. CONCLUSIONS
Nonenhanced helical CT and change in resistive index are useful diagnostic tools that can replace IVP for the diagnosis of acute unilateral ureteral obstruction. Each technique has its own merits and limitations. Therefore, the choice between techniques depends on the medical resources, relative costs and radiological experience at a particular health system. REFERENCES
1. Labrecque, M., Dostaler, L. P., Rousselle, R. et al: Efficacy of nonsteroidal anti-inflammatory drugs in the treatment of acute renal colic. A meta-analysis. Arch Intern Med, 154: 1381, 1994 2. Shokeir, A. A., Mahran, M. R. and Abdulmaaboud, M.: Renal colic in pregnant women: role of renal resistive index. Urology, 55: 344, 2000 3. Smith, R. C., Rosenfield, A. T., Choe, K. A. et al: Acute flank pain: comparison of non-contrast-enhanced CT and intravenous urography. Radiology, 194: 789, 1995 4. Dalrymple, N. C., Verga, M., Anderson, K. R. et al: The value of unenhanced helical computerized tomography in the management of acute flank pain. J Urol, 159: 735, 1998 5. Miller, O. F., Rineer, S. K., Reichard, S. R. et al: Prospective comparison of unenhanced spiral computed tomography and intravenous urogram in the evaluation of acute flank pain. Urology, 52: 982, 1998 6. Fielding, J. R., Steele, G., Fox, L. A. et al: Spiral computerized tomography in the evaluation of acute flank pain: a replacement for excretory urography. J Urol, 157: 2071, 1997 7. Yilmaz, S., Sindel, T., Arshan, G. et al: Renal colic: comparison of spiral CT, US and IVU in the detection of ureteral calculi. Eur Radiol, 8: 212, 1998 8. Vieweg, J., Teh, C., Freed, K. et al: Unenhanced helical computerized tomography for the evaluation of patients with acute flank pain. J Urol, 160: 679, 1998 9. Shokeir, A. A. and Abdulmaaboud, M.: Resistive index in renal colic: a prospective study. BJU Int, 83: 378, 1999 10. de Toledo, L. S., Martinez-Berganza Asensio, T., Cozcolluela Cabrejas, R. et al: Doppler-duplex ultrasound in renal colic. Eur J Radiol, 23: 143, 1996 11. Opdenakker, L., Oyen, R., Vervloessem, I. et al: Acute obstruction of the renal collecting system: the intrarenal resistive index is a useful yet time-dependent parameter for diagnosis. Eur Radiol, 8: 1429, 1998 12. Shokeir, A. A., Abdulmaaboud, M., Farage, Y. et al: Resistive index in renal colic: the effect of nonsteroidal antiinflammatory drugs. BJU Int, 84: 249, 1999
Vol. 165, 1082–1084, April 2001 Printed in U.S.A.
PROSPECTIVE COMPARISON OF NONENHANCED HELICAL COMPUTERIZED TOMOGRAPHY AND DOPPLER ULTRASONOGRAPHY FOR THE DIAGNOSIS OF RENAL COLIC AHMED A. SHOKEIR
AND
MAGDY ABDULMAABOUD
From the Urology and Nephrology Center and Radiology Department, Mansoura University, Mansoura, Egypt
ABSTRACT
Purpose: We evaluate the accuracy of nonenhanced helical computerized tomography (CT) and Doppler ultrasonography for the diagnosis of renal colic. Materials and Methods: Our study includes 109 patients, with 218 kidneys, who presented with unilateral flank pain. All patients underwent nonenhanced helical CT, Doppler ultrasonography and excretory urography (IVP). CT was evaluated for the presence of ureteral stones and manifestation of ureteral obstruction. For Doppler ultrasonography the renal resistive index was measured for the left and right kidneys in each patient, and change in resistive index between ipsilateral and contralateral kidneys was calculated and considered positive for ureteral obstruction with values 0.04 or greater. As a reference standard, absence of obstruction was considered if IVP was negative and the cause of flank pain was confirmed not to be urological. Obstruction was diagnosed not only by positive IVP, but also by patient followup until passage or retrieval of ureteral stones. Results of CT and change in resistive index were compared with those of the reference standard. Results: Unilateral ureteral obstruction was confirmed in 52 patients, while no obstruction was found in 57. Of the 57 patients without ureterolithiasis the change in resistive index results was negative in all patients with a specificity of 100%, while CT was negative in 55 with a specificity of 96%. Of the 52 patients with ureteral obstruction CT was positive in 50, and change in resistive index was positive in 47 with a sensitivity of 96% and 90%, respectively, with a difference of no significant value. Conclusions: Nonenhanced helical CT and change in resistive index are sensitive and specific tests that can contribute significantly to the diagnosis of acute unilateral renal obstruction. They can replace IVP, particularly in situations in which it is undesirable. KEY WORDS: kidney; ureter; ureteral obstruction; colic; tomography, x-ray computed
Acute renal colic is one of the most anguishing forms of pain in humans that needs quick diagnosis and treatment. The magnitude of the problem is large worldwide, and the lifetime risk of an attack of acute renal colic is estimated at 1% to 10%.1 It is caused by acute partial ureteral obstruction due to a calculus in the vast majority of cases. Traditionally, besides routine clinical examination, acute renal colic has been diagnosed with routine plain film of the kidneys, ureters and bladder, conventional gray-scale ultrasonography and excretory urography (IVP). During the last few years, the introduction of noncontrast computerized tomography (CT) and Doppler ultrasonography has changed the strategy of diagnosis of renal colic. We evaluate the diagnostic accuracy of the recent nonenhanced helical CT and Doppler ultrasonography for renal colic. MATERIALS AND METHODS
Between March and October 1999 each patient presenting with acute unilateral flank pain at the emergency department or urology clinic of New Jeddah Clinic Hospital was enrolled in the study. Patients were excluded from study if they presented with serum creatinine greater than 2 mg./dl., pregnancy, allergy to radiocontrast, bilateral flank pain or a
solitary kidney. A total of 170 patients were eligible and 125 agreed to participate. After informed consent all patients underwent nonenhanced helical CT, Doppler ultrasonography and then IVP. Radiography was performed before giving medications in most and during an attack of loin pain in all patients. Patients diagnosed as having ureteral stones were followed until passage or retrieval of stones. Nonenhanced helical CT was performed with a Sytec SRI* scanner. No oral or intravenous contrast material was used. Spiral scans were performed from the top of the kidney to the bladder base with the table feed rate at 5 mm. per rotation and a nominal section thickness of 5 mm. (pitch ⫽ 1). Image reconstruction was routinely performed at 5 mm. increments with 360 degree interpolation. When calcific density was seen along the course of the ureter, further evaluation of this region was performed with retrospective reconstruction in 2 mm. increments. In some patients reformatted images were also obtained with overlapped sections in 2 mm. intervals to create images similar to IVP. CT was considered diagnostic of ureterolithiasis if a calculus was seen in the ureter with or without secondary signs of obstruction, including ureteral or renal dilatation, soft tissue ring sign, loss of renal pelvic fat planes or perinephric stranding. A stone obstructing the right pelviureteral junction and causing dilation of the renal pelvis is shown in figure 1, A. The ring sign denotes visualization of a rim of soft tissue surrounding a stone (fig. 1, B). This sign represents the edematous wall of the ureter and is helpful in distinguishing stones from phleboliths (fig. 1, C).
Accepted for publication October 6, 2000. Editor’s Note: This article is the first of 5 published in this issue for which category 1 CME credits can be earned. Instructions for obtaining credits are given with the questions on pages 1264 and 1265. *General Electric, Milwaukee, Wisconsin. 1082
1083
COMPUTERIZED TOMOGRAPHY VERSUS ULTRASONOGRAPHY FOR RENAL COLIC
FIG. 1. Nonenhanced helical CT of stone at right (R) pelviureteral junction (arrow) with secondary dilatation of renal pelvis (A), of stone in pelvic part of left (L) ureter with soft tissue ring sign (arrow) (B) and of right pelvic phlebolith (arrow) simulating ureteral stone but without ring sign (C).
Doppler ultrasonography was performed using an SSD2000† multiview unit with a transducer frequency of 3.5 MHz. At least 5 Doppler spectra were obtained from more than 3 regions in each kidney. Doppler signals were obtained from arcuate arteries at the corticomedullary junctions, interlobar arteries along the border of the medullary pyramids or both. The Doppler waveforms were made using the lowest pulse repetition frequency possible without aliasing. This procedure maximized the size of the Doppler spectrum and decreased the percentage error in the measurements. In addition, the lowest possible wall filter for each ultrasound scanner was used. The Doppler sample width was set at 2 to 5 mm. The renal resistive index was calculated as peak systolic velocity-end diastolic velocity/peak systolic velocity, with change in resistive index determined as the change in resistive index of the corresponding and contralateral kidneys. Values of and change in resistive index used for statistical analysis were totaled by mean measurements in individual patients. Doppler ultrasonography was considered positive for obstruction if change in resistive index was 0.04 or greater.2 Doppler ultrasonography of a patient with left renal colic is shown in figure 2. IVP was performed in standard fashion with 50 to 100 cc iopromide nonionic contrast, and was interpreted as negative with a nonequivocal normal reno-ureteral unit and as positive with hydroureter proximal to a ureteral stone with delayed pelvicaliceal filling with contrast medium. As a reference standard, absence of obstruction was considered if IVP was negative and the cause of flank pain was confirmed not to be urological. Obstruction was diagnosed not only by positive IVP, but also by patient followup until passage or retrieval of ureteral stones. The sensitivity, specificity and overall accuracy of CT and change in resistive index for the diagnosis of acute unilateral ureteral obstruction were calculated. Differences were assessed using the chi-square and student t tests, as appropriate. †Aloka, Tokyo, Japan.
RESULTS
Of the 125 patients who agreed to participate in the study 10 were lost to followup and 6 had equivocal or suboptimal IVP results. The study group included 109 patients with 218 kidneys. There were 77 males and 32 females with a total mean age of 39 years (range 19 to 61). Flank pain affected the right side in 69 and the left side in 40 patients. No ureteral obstruction was found in 57 patients. IVP showed that the left and right kidneys were normal and the cause of loin pain was confirmed not to be urological, including radiculitis in 10 patients, myositis in 14, appendicitis in 7, colitis in 9 and biliary colic in 17. Obstruction was diagnosed in 52 patients, and IVP showed nonequivocal evidence of unilateral ureteral obstruction with a normal contralateral kidney. Moreover, ureteral obstruction was confirmed by patient followup, including 40 who noticed spontaneous passage of stones during medical treatment and the remaining 12 underwent ureteroscopy with stone extraction. Of the 57 patients without ureterolithiasis CT was negative in all but 2 in whom pelvic phleboliths were interpreted as ureteral stones. In 7 patients there were calcifications that were not ureteral calculi, including pelvic phleboliths in 2, nonobstructing renal calculi in 2, calcified ovarian mass in 1, calcified uterine mass in 1 and calcified mesenteric lymph nodes in 1. Of the 52 patients with ureteral calculi CT documented stones with 1 or more of the secondary signs of obstruction in 50. In the remaining 2 patients with ureteral stones CT showed no evidence of calculus or obstruction. The agreement between CT results and those of the reference standard is given in the table. CT showed a sensitivity of 96%, a specificity of 96% and an overall accuracy of 96%. Mean resistive index plus or minus standard deviation was 0.685 ⫾ 0.03 in the 52 obstructed kidneys, significantly higher than that of 0.616 ⫾ 0.04 in the 166 normal kidneys (p ⬍0.001). Mean change in resistive index of patients with acute unilateral ureteral obstruction was significantly higher than that of those in whom the left and right kidneys were normal, at 0.059 ⫾ 0.01 and 0.005 ⫾ 0.003, respectively (p ⬍0.0001). The agreement between change in resistive index and the reference standard results for the diagnosis of acute unilateral ureteral obstruction is given in the table. Change in resistive index was sensitive in 90%, specific in
Agreement between nonenhanced helical CT and change in resistive index versus the reference standard for the diagnosis of acute unilateral ureteral obstruction in 109 patients Predicted Results
FIG. 2. Doppler ultrasonography of patient with left (L) renal colic. Resistive index (RI) is 0.72 for obstructed left kidney (A) and 0.63 for normal right (R) kidney (B). Change in resistive index between left and right kidneys is 0.09.
CT: Pos. Neg. Change in resistive index: Pos. Neg.
Reference Standard No. Pos.
No. Neg.
50 2
2 55
47 5
0 57
1084
COMPUTERIZED TOMOGRAPHY VERSUS ULTRASONOGRAPHY FOR RENAL COLIC
100% and accurate in 95% of patients. Comparison between these results and those of CT showed no significant difference. DISCUSSION
To our knowledge Smith et al were the first to advocate the use of noncontrast CT for the diagnosis of acute renal colic.3 Our present series has confirmed several recent studies that noncontrast CT is an accurate radiographic modality for evaluation of renal colic.4 – 8 The potential benefit of noncontrast CT is the use of it in patients with contrast allergies, those with preexisting renal failure and those with an unclear clinical diagnosis mimicking renal colic. In addition, CT can visualize all stones regardless of composition. The procedure takes only 5 minutes and at some health systems it has been estimated to cost no more than IVP. Besides stone visualization, several secondary CT signs of ureteral obstruction are often present and useful when a stone is not readily identified. In our series nonenhanced helical CT was sensitive in 96% and specific in 96% of patients diagnosed with renal colic. Moreover, CT identified other urinary and nonurinary abnormalities in 7 patients and directed further imaging and treatment. There are a number of potential pitfalls in the interpretation of CT. Phleboliths in the pelvis can often be seen along the normal anatomical course of the ureter and can mimic ureteral stones. The ring sign is helpful for distinguishing stones from phleboliths. A gonadal vein can sometimes be confused with a dilated ureter and can be distinguished by following the superior course of the structure in question. The main disadvantage of noncontrast CT compared to IVP is the absence of renal function evaluation. Moreover, radiation exposure of CT is generally higher, limiting use during pregnancy. In addition, CT services are not universally available, particularly for a 24-hour period, and a radiologist is required for the accurate interpretation of the films. Results of our present series have confirmed the recent observation that Doppler ultrasonography is a sensitive and specific method for the diagnosis of renal colic.2, 9 –11 The noninvasive nature of Doppler ultrasonography gives it a considerable appeal in potential application, particularly in situations in which IVP is not recommended, such as renal impairment and pregnancy. We have shown that change in resistive index is more useful for the diagnosis of acute renal colic than a solid value of resistive index, and that a change in resistive index 0.04 or greater gives the highest sensitivity and specificity.2 Nevertheless, in patients with solitary kidneys or those with bilateral renal obstruction, albeit clinically uncommon, change in resistive index is of no value. The diagnostic accuracy of this index may be decreased if the patients were given nonsteroidal anti-inflammatory drugs.12 Therefore, to achieve the highest diagnostic accuracy we recommend that Doppler ultrasonography, which is operator dependent and requires special experience, be performed before giving nonsteroidal anti-inflammatory drugs and during an attack of pain. The diagnostic approach of acute flank pain is controversial and can vary from center to center, city to city or country to country depending on what is considered acceptable. Important factors include the local prevalence of stone disease, medical resources available, relative costs in a particular system, and the merits and limitations of each diagnostic modality. However, there is an increasing trend towards noninvasive or minimally invasive procedures. Many cases
could be diagnosed with initial screening by clinical examination, plain film of kidneys, ureters and bladder, and conventional ultrasonography. Noninvasive Doppler ultrasonography, with a change in resistive index of 0.04 as the dividing line between obstruction and no obstruction, is helpful for equivocal cases. Noncontrast CT is a sensitive and specific test. However, because of some limitations it is our opinion that it be reserved for patients in whom plain film of kidneys, ureters and bladder, and ultrasonography with Doppler assistance could not complete the diagnosis. IVP is used for diagnosis in a few patients in whom other noninvasive procedures are indeterminate. Nevertheless, IVP is indispensable if interventional treatment is planned. A noteworthy observation is that approximately 5% of patients were excluded from the study because of equivocal or suboptimal IVP results. Since IVP was part of the reference standard, a bias could have been introduced into the study. Another potential source of bias is that the interpreters of the study were not blinded to the results of the competing modalities. CONCLUSIONS
Nonenhanced helical CT and change in resistive index are useful diagnostic tools that can replace IVP for the diagnosis of acute unilateral ureteral obstruction. Each technique has its own merits and limitations. Therefore, the choice between techniques depends on the medical resources, relative costs and radiological experience at a particular health system. REFERENCES
1. Labrecque, M., Dostaler, L. P., Rousselle, R. et al: Efficacy of nonsteroidal anti-inflammatory drugs in the treatment of acute renal colic. A meta-analysis. Arch Intern Med, 154: 1381, 1994 2. Shokeir, A. A., Mahran, M. R. and Abdulmaaboud, M.: Renal colic in pregnant women: role of renal resistive index. Urology, 55: 344, 2000 3. Smith, R. C., Rosenfield, A. T., Choe, K. A. et al: Acute flank pain: comparison of non-contrast-enhanced CT and intravenous urography. Radiology, 194: 789, 1995 4. Dalrymple, N. C., Verga, M., Anderson, K. R. et al: The value of unenhanced helical computerized tomography in the management of acute flank pain. J Urol, 159: 735, 1998 5. Miller, O. F., Rineer, S. K., Reichard, S. R. et al: Prospective comparison of unenhanced spiral computed tomography and intravenous urogram in the evaluation of acute flank pain. Urology, 52: 982, 1998 6. Fielding, J. R., Steele, G., Fox, L. A. et al: Spiral computerized tomography in the evaluation of acute flank pain: a replacement for excretory urography. J Urol, 157: 2071, 1997 7. Yilmaz, S., Sindel, T., Arshan, G. et al: Renal colic: comparison of spiral CT, US and IVU in the detection of ureteral calculi. Eur Radiol, 8: 212, 1998 8. Vieweg, J., Teh, C., Freed, K. et al: Unenhanced helical computerized tomography for the evaluation of patients with acute flank pain. J Urol, 160: 679, 1998 9. Shokeir, A. A. and Abdulmaaboud, M.: Resistive index in renal colic: a prospective study. BJU Int, 83: 378, 1999 10. de Toledo, L. S., Martinez-Berganza Asensio, T., Cozcolluela Cabrejas, R. et al: Doppler-duplex ultrasound in renal colic. Eur J Radiol, 23: 143, 1996 11. Opdenakker, L., Oyen, R., Vervloessem, I. et al: Acute obstruction of the renal collecting system: the intrarenal resistive index is a useful yet time-dependent parameter for diagnosis. Eur Radiol, 8: 1429, 1998 12. Shokeir, A. A., Abdulmaaboud, M., Farage, Y. et al: Resistive index in renal colic: the effect of nonsteroidal antiinflammatory drugs. BJU Int, 84: 249, 1999