- Email: [email protected]
Genitourinary Imaging With Noncontrast Computerized Tomography—Are We Missing Duplex Ureters?
Voiding Dysfunction Genitourinary Imaging With Noncontrast Computerized Tomography—Are We Missing Duplex Ureters? Brian H. Eisner,* Mehrine Shaikh, Raul N. Uppot, Dushyant V. Sahani and Stephen P. Dretler From the Kidney Stone Center, Department of Urology and Department of Radiology (BS, RNU, DVS), Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
Purpose: Noncontrast computerized tomography has replaced excretory urography as the first line diagnostic tool for evaluating nephrolithiasis at many centers. We evaluated the ability of noncontrast computerized tomography to detect ureteral duplication to determine how frequently these anomalies are under diagnosed. Materials and Methods: Computerized tomography images of 14 patients with known ureteral duplication who had previously undergone noncontrast and contrast enhanced computerized tomography and 5 control patients with normal ureteral anatomy were interpreted by 2 blinded radiologists who specialize in genitourinary imaging. Results: The sensitivity of axial computerized tomography with contrast material, axial computerized tomography without contrast material and coronal computerized tomography without contrast material was 96%, 59% and 65%, respectively. The negative predictive value of axial computerized tomography with contrast material, axial computerized tomography without contrast material and coronal computerized tomography without contrast material was 95%, 65% and 67%, respectively. The accuracy of axial computerized tomography with contrast medium was significantly higher than that of noncontrast axial or noncontrast coronal computerized tomography (each p ⬍0.01). Conclusions: Duplicated ureters, which represent a challenge to the endourologist, are under diagnosed on noncontrast computerized tomography. Urologists and radiologists should be aware of this limitation and contrast studies should be done when anatomical anomalies are suspected. Key Words: ureter; abnormalities; tomography, emission-computed; diagnosis
enal duplication is a common congenital anomaly with a reported prevalence of 0.3 to 6%.1,2 Up to 20% of patients remain asymptomatic into adulthood.2 The patient with a duplex ureter and ureterolithiasis represents a challenge to the endoscopist who does not recognize the presence of this anatomical variant. Historically asymptomatic duplex ureters in patients with nephrolithiasis were discovered by excretory urogram.3 However, since the introduction in 1995 of noncontrast helical CT to evaluate ureteral colic,4,5 groups at many centers no longer routinely perform excretory urography to evaluate adults with suspected nephrolithiasis. We hypothesize that, since excretory urography has largely been replaced by noncontrast CT for evaluating renal colic, the preoperative identification of adults with ureteral duplication has become less frequent, which may result in confusion and mismanagement during ureteroscopy. Therefore, we determined the accuracy of diagnosing ureteral duplication using unenhanced CT.
R
MATERIALS AND METHODS A radiological and urological surgery database was searched to identify patients with duplex ureters who had undergone noncontrast and contrast enhanced helical CT of the abdoSubmitted for publication August 6, 2007. * Correspondence: Department of Urology, Massachusetts General Hospital, 55 Fruit St., Boston, Massachusetts 02114 (telephone: 617-726-2797; FAX: 617-726-6131; e-mail: [email protected]).
0022-5347/08/1794-1445/0 THE JOURNAL OF UROLOGY® Copyright © 2008 by AMERICAN UROLOGICAL ASSOCIATION
men between 1998 and 2005. A total of 14 patients met these inclusion criteria and their records were subsequently analyzed. Axial and coronal CT images were reviewed independently by 2 radiologists who specialize in genitourinary imaging. Each ureter was rated as single or duplex. Statistical analysis was used to determine sensitivity and predictive value, and compare overall accuracy for detecting duplex ureters. Noncontrast CT was compared with the gold standard, contrast enhanced CT. Analysis was performed of individual radiologist analyses as well as combined analyses. Helical CT CT was acquired on 4, 8 and 16 slice multidetector CT images. It was performed as a stone protocol CT, in which no oral or intravenous contrast medium was administered, or as hematuria protocol CT, in which intravenous contrast medium was administered using 120 cc contrast material with a 100-second delay and a second 9-minute delayed image. All images were acquired using 2.5 mm sections from the level of the diaphragm to the pubic symphysis. Images were also reformatted to the coronal plane. RESULTS Table 1 lists patient demographic data. Two of the 14 patients had bilateral ureteral duplication and, therefore, the total number of kidneys with duplex ureters studied was 16 and the number with a single ureter was 12. Five duplex
1445
Vol. 179, 1445-1448, April 2008 Printed in U.S.A. DOI:10.1016/j.juro.2007.11.074
1446
GENITOURINARY IMAGING WITH NONCONTRAST COMPUTERIZED TOMOGRAPHY TABLE 1. Patient demographic data
No. pts Mean age (range) No. men/women No. lt/rt duplex ureter No. with bilat duplex ureter No. complete/partial ureteral duplication No. 4/8/16 scanner type multidetector CT slice
14 48.8 (33.9–67.4) 6/8 10/6 2 5/11 8/3/3
ureters were complete duplications and 11 were partially duplicated, Y-shaped ureters. Overall sensitivity for detecting duplex ureters in this study of contrast enhanced axial CT, noncontrast axial CT and noncontrast coronal CT was 96%, 59% and 63%, respectively. NPV for contrast enhanced axial CT, noncontrast axial CT and noncontrast coronal CT was 95%, 65% and 66%, respectively (table 2). When combining noncontrast axial and noncontrast coronal imaging data on each of the 10 patients (20 renal units), sensitivity was 70% and NPV was 70%. The accuracy of contrast enhanced axial CT for detecting duplex ureters was significantly higher than that of noncontrast axial or noncontrast coronal CT (each chi square test p ⬍0.01). Figures 1 to 4 show examples of CT images. Renal length was measured on coronal imaging. There was no difference between single system and duplex kidneys (mean cephalocaudal length 10.4 cm, range 8.2 to 11.9 and 9.9, range 8.0 to 12.5, respectively). In patients with 1 duplex kidney and 1 contralateral single system kidney cephalocaudal length of the duplex kidney was greater in 31% of patients.
FIG. 1. Noncontrast axial image of patient with duplex ureter. Arrow indicates ureter, which was easily visualized.
DISCUSSION Since its description in 1995, noncontrast CT has become the first line examination in many patients with renal colic.4 The speed, accuracy of stone identification and lack of use of intravenous contrast medium are the main advantages of this modality.5 Although groups at some centers still use excretory urography,3 CT has become the gold standard for evaluating patients with flank pain, providing superior diagnostic accuracy in the acute setting as well as greater usefulness in treatment planning compared with excretory urography.5–7 Whereas noncontrast CT is efficacious for diagnosing ureterolithiasis, contrast enhanced imaging is the gold standard for evaluating ureteral anatomical anomalies.8 Patients with previously asymptomatic duplex ureters and acute ureteral colic represent a challenge to the unsuspecting urologist. Knowledge of a second ipsilateral orifice in cases of complete ureteral duplication or the location of a
TABLE 2. Sensitivity and NPV for detecting duplex ureter
Contrast enhanced axial CT: Sensitivity NPV Noncontrast axial CT: Sensitivity NPV Noncontrast CT: Sensitivity NPV
% Radiologist 1
% Radiologist 2
Overall %
100 100
92 91
96 95
50 60
68 71
59 65
67 67
63 67
65 67
FIG. 2. Contrast enhanced axial image of patient with duplex ureter. Second ureter is visualized that was not seen on noncontrast images.
GENITOURINARY IMAGING WITH NONCONTRAST COMPUTERIZED TOMOGRAPHY
1447
the radiologists in our study did without the aid of intravenous contrast material. A limitation of this study was that, although the participating radiologists (DVS and RNU) were blinded to which ureters were duplex, they were not blinded to the purpose of the study. This limitation is applicable to noncontrast CT as well as to the gold standard in this study, that is contrast enhanced CT. As described, all CT images were analyzed by these 2 radiologists. However, before the initiation of our study it was noted that the radiologists who previously interpreted the scans often failed to comment on duplex ureters because they were thought to be an incidental finding even in cases when contrast material was administered and their presence was obvious. Therefore, for reviewing CT images in this study the participating radiologists were made aware of the purpose of the study so that they would comment on the presence or absence of duplex ureters. This study analyzed a relatively small number of patients, that is 14 during a 7-year span. Although the reported incidence of duplex ureters is 0.3% to 6%,1,2 most adults with this asymptomatic anatomical variant are likely not affected by nephrolithiasis and, therefore, they
FIG. 3. Noncontrast coronal image of patient with duplex ureter. Arrow indicates ureter, which was easily visualized.
branch point of a partially duplicated Y-shaped ureter is essential to the ureteroscopist for endoscopic treatment of ureteral calculi. Those who do not consider these anatomical variants may waste time unsuccessfully searching for a calculus in the wrong location or incorrectly conclude that the stone has passed or is outside the urinary tract. Historically, in addition to contrast visualization of 2 separate ureters, renal length has been used to identify patients with duplex systems. However, although duplex kidneys may be longer than nonduplex kidneys, the presence of 2 ureters is more sensitive for diagnosing duplex kidneys than length measurements. In a study of CT in 26 adult patients with duplex kidneys 4 (15%) had an atrophic renal moiety and, therefore, a duplex kidney of normal length.9 In the current study renal length was not helpful for distinguishing single from duplex kidneys with no difference in mean renal length. Furthermore, duplex kidneys were the larger kidney in 31% of our cases. The findings of the current study should encourage the urologist to be vigilant when interpreting noncontrast CT in the setting of ureteral colic. Axial or coronal noncontrast CT was at best 70% sensitive for detecting duplex ureters compared with 95% sensitivity for contrast enhanced CT. The superior accuracy of contrast enhanced CT was statistically significant (p ⬍0.01). Furthermore, this study probably overestimates the accuracy of diagnosis using noncontrast CT. The radiologists who participated specialize in genitourinary imaging and focus exclusively on abdominal imaging. We believe that in the real world most radiologists do not focus on the presence or absence of a duplex ureter and they might not recognize asymptomatic patients as frequently as
FIG. 4. Contrast enhanced coronal image of patient with duplex ureter. Second ureter was visualized that was not seen on noncontrast images.
1448
GENITOURINARY IMAGING WITH NONCONTRAST COMPUTERIZED TOMOGRAPHY
do not come to the attention of a urologist. However, given the lifetime prevalence of symptomatic nephrolithiasis (10% of men and 4% of women),10 it is reasonable to assume that urologists who treat a large number of patients with nephrolithiasis will encounter this anatomical variant 1 or more times in their careers. Being mindful of this is helpful in the diagnosis and treatment of these patients.
4.
5.
6.
Abbreviations and Acronyms CT ⫽ computerized tomography NPV ⫽ negative predictive value
7.
8.
REFERENCES 1.
Hartman GW and Hodson CJ: The duplex kidney and related abnormalities. Clin Radiol 1969; 20: 387. 2. Privett JT, Jeans WD and Roylance J: The incidence and importance of renal duplication. Clin Radiol 1976; 27: 521. 3. Mutazindwa T and Husseini T: Imaging in acute renal colic: the intravenous urogram remains the gold standard. Eur J Radiol 1996; 23: 238.
9.
10.
Smith RC, Rosenfield AT, Choe KA, Essenmacher KR, Verga M, Glickman MG et al: Acute flank pain: comparison of non-contrast-enhanced CT and intravenous urography. Radiology 1995; 194: 789. Ripolles T, Agramunt M, Errando J, Martinez MJ, Coronel B and Morales M: Suspected ureteral colic: plain film and sonography vs unenhanced helical CT. A prospective study in 66 patients. Eur Radiol 2004; 14: 129. Chen MY and Zagoria RJ: Can noncontrast helical computed tomography replace intravenous urography for evaluation of patients with acute urinary tract colic? J Emerg Med 1999; 17: 299. Katz DS, Lane MJ and Sommer FG: Unenhanced helical CT of ureteral stones: incidence of associated urinary tract findings. AJR Am J Roentgenol 1996; 166: 1319. Caoili EM, Cohan RH, Korobkin M, Platt JF, Francis IR, Faerber GJ et al: Urinary tract abnormalities: initial experience with multi-detector row CT urography. Radiology 2002; 222: 353. Zissin R, Apter S, Yaffe D, Knots E, Gayer G, Nissenkorn I et al: Renal duplication with associated complications in adults: CT findings in 26 cases. Clin Radiol 2001; 56: 58. Soucie JM, Thun MJ, Coates RJ, McClellan W and Austin H: Demographic and geographic variability of kidney stones in the united states. Kidney Int 1994; 46: 893.
Purpose: Noncontrast computerized tomography has replaced excretory urography as the first line diagnostic tool for evaluating nephrolithiasis at many centers. We evaluated the ability of noncontrast computerized tomography to detect ureteral duplication to determine how frequently these anomalies are under diagnosed. Materials and Methods: Computerized tomography images of 14 patients with known ureteral duplication who had previously undergone noncontrast and contrast enhanced computerized tomography and 5 control patients with normal ureteral anatomy were interpreted by 2 blinded radiologists who specialize in genitourinary imaging. Results: The sensitivity of axial computerized tomography with contrast material, axial computerized tomography without contrast material and coronal computerized tomography without contrast material was 96%, 59% and 65%, respectively. The negative predictive value of axial computerized tomography with contrast material, axial computerized tomography without contrast material and coronal computerized tomography without contrast material was 95%, 65% and 67%, respectively. The accuracy of axial computerized tomography with contrast medium was significantly higher than that of noncontrast axial or noncontrast coronal computerized tomography (each p ⬍0.01). Conclusions: Duplicated ureters, which represent a challenge to the endourologist, are under diagnosed on noncontrast computerized tomography. Urologists and radiologists should be aware of this limitation and contrast studies should be done when anatomical anomalies are suspected. Key Words: ureter; abnormalities; tomography, emission-computed; diagnosis
enal duplication is a common congenital anomaly with a reported prevalence of 0.3 to 6%.1,2 Up to 20% of patients remain asymptomatic into adulthood.2 The patient with a duplex ureter and ureterolithiasis represents a challenge to the endoscopist who does not recognize the presence of this anatomical variant. Historically asymptomatic duplex ureters in patients with nephrolithiasis were discovered by excretory urogram.3 However, since the introduction in 1995 of noncontrast helical CT to evaluate ureteral colic,4,5 groups at many centers no longer routinely perform excretory urography to evaluate adults with suspected nephrolithiasis. We hypothesize that, since excretory urography has largely been replaced by noncontrast CT for evaluating renal colic, the preoperative identification of adults with ureteral duplication has become less frequent, which may result in confusion and mismanagement during ureteroscopy. Therefore, we determined the accuracy of diagnosing ureteral duplication using unenhanced CT.
R
MATERIALS AND METHODS A radiological and urological surgery database was searched to identify patients with duplex ureters who had undergone noncontrast and contrast enhanced helical CT of the abdoSubmitted for publication August 6, 2007. * Correspondence: Department of Urology, Massachusetts General Hospital, 55 Fruit St., Boston, Massachusetts 02114 (telephone: 617-726-2797; FAX: 617-726-6131; e-mail: [email protected]).
0022-5347/08/1794-1445/0 THE JOURNAL OF UROLOGY® Copyright © 2008 by AMERICAN UROLOGICAL ASSOCIATION
men between 1998 and 2005. A total of 14 patients met these inclusion criteria and their records were subsequently analyzed. Axial and coronal CT images were reviewed independently by 2 radiologists who specialize in genitourinary imaging. Each ureter was rated as single or duplex. Statistical analysis was used to determine sensitivity and predictive value, and compare overall accuracy for detecting duplex ureters. Noncontrast CT was compared with the gold standard, contrast enhanced CT. Analysis was performed of individual radiologist analyses as well as combined analyses. Helical CT CT was acquired on 4, 8 and 16 slice multidetector CT images. It was performed as a stone protocol CT, in which no oral or intravenous contrast medium was administered, or as hematuria protocol CT, in which intravenous contrast medium was administered using 120 cc contrast material with a 100-second delay and a second 9-minute delayed image. All images were acquired using 2.5 mm sections from the level of the diaphragm to the pubic symphysis. Images were also reformatted to the coronal plane. RESULTS Table 1 lists patient demographic data. Two of the 14 patients had bilateral ureteral duplication and, therefore, the total number of kidneys with duplex ureters studied was 16 and the number with a single ureter was 12. Five duplex
1445
Vol. 179, 1445-1448, April 2008 Printed in U.S.A. DOI:10.1016/j.juro.2007.11.074
1446
GENITOURINARY IMAGING WITH NONCONTRAST COMPUTERIZED TOMOGRAPHY TABLE 1. Patient demographic data
No. pts Mean age (range) No. men/women No. lt/rt duplex ureter No. with bilat duplex ureter No. complete/partial ureteral duplication No. 4/8/16 scanner type multidetector CT slice
14 48.8 (33.9–67.4) 6/8 10/6 2 5/11 8/3/3
ureters were complete duplications and 11 were partially duplicated, Y-shaped ureters. Overall sensitivity for detecting duplex ureters in this study of contrast enhanced axial CT, noncontrast axial CT and noncontrast coronal CT was 96%, 59% and 63%, respectively. NPV for contrast enhanced axial CT, noncontrast axial CT and noncontrast coronal CT was 95%, 65% and 66%, respectively (table 2). When combining noncontrast axial and noncontrast coronal imaging data on each of the 10 patients (20 renal units), sensitivity was 70% and NPV was 70%. The accuracy of contrast enhanced axial CT for detecting duplex ureters was significantly higher than that of noncontrast axial or noncontrast coronal CT (each chi square test p ⬍0.01). Figures 1 to 4 show examples of CT images. Renal length was measured on coronal imaging. There was no difference between single system and duplex kidneys (mean cephalocaudal length 10.4 cm, range 8.2 to 11.9 and 9.9, range 8.0 to 12.5, respectively). In patients with 1 duplex kidney and 1 contralateral single system kidney cephalocaudal length of the duplex kidney was greater in 31% of patients.
FIG. 1. Noncontrast axial image of patient with duplex ureter. Arrow indicates ureter, which was easily visualized.
DISCUSSION Since its description in 1995, noncontrast CT has become the first line examination in many patients with renal colic.4 The speed, accuracy of stone identification and lack of use of intravenous contrast medium are the main advantages of this modality.5 Although groups at some centers still use excretory urography,3 CT has become the gold standard for evaluating patients with flank pain, providing superior diagnostic accuracy in the acute setting as well as greater usefulness in treatment planning compared with excretory urography.5–7 Whereas noncontrast CT is efficacious for diagnosing ureterolithiasis, contrast enhanced imaging is the gold standard for evaluating ureteral anatomical anomalies.8 Patients with previously asymptomatic duplex ureters and acute ureteral colic represent a challenge to the unsuspecting urologist. Knowledge of a second ipsilateral orifice in cases of complete ureteral duplication or the location of a
TABLE 2. Sensitivity and NPV for detecting duplex ureter
Contrast enhanced axial CT: Sensitivity NPV Noncontrast axial CT: Sensitivity NPV Noncontrast CT: Sensitivity NPV
% Radiologist 1
% Radiologist 2
Overall %
100 100
92 91
96 95
50 60
68 71
59 65
67 67
63 67
65 67
FIG. 2. Contrast enhanced axial image of patient with duplex ureter. Second ureter is visualized that was not seen on noncontrast images.
GENITOURINARY IMAGING WITH NONCONTRAST COMPUTERIZED TOMOGRAPHY
1447
the radiologists in our study did without the aid of intravenous contrast material. A limitation of this study was that, although the participating radiologists (DVS and RNU) were blinded to which ureters were duplex, they were not blinded to the purpose of the study. This limitation is applicable to noncontrast CT as well as to the gold standard in this study, that is contrast enhanced CT. As described, all CT images were analyzed by these 2 radiologists. However, before the initiation of our study it was noted that the radiologists who previously interpreted the scans often failed to comment on duplex ureters because they were thought to be an incidental finding even in cases when contrast material was administered and their presence was obvious. Therefore, for reviewing CT images in this study the participating radiologists were made aware of the purpose of the study so that they would comment on the presence or absence of duplex ureters. This study analyzed a relatively small number of patients, that is 14 during a 7-year span. Although the reported incidence of duplex ureters is 0.3% to 6%,1,2 most adults with this asymptomatic anatomical variant are likely not affected by nephrolithiasis and, therefore, they
FIG. 3. Noncontrast coronal image of patient with duplex ureter. Arrow indicates ureter, which was easily visualized.
branch point of a partially duplicated Y-shaped ureter is essential to the ureteroscopist for endoscopic treatment of ureteral calculi. Those who do not consider these anatomical variants may waste time unsuccessfully searching for a calculus in the wrong location or incorrectly conclude that the stone has passed or is outside the urinary tract. Historically, in addition to contrast visualization of 2 separate ureters, renal length has been used to identify patients with duplex systems. However, although duplex kidneys may be longer than nonduplex kidneys, the presence of 2 ureters is more sensitive for diagnosing duplex kidneys than length measurements. In a study of CT in 26 adult patients with duplex kidneys 4 (15%) had an atrophic renal moiety and, therefore, a duplex kidney of normal length.9 In the current study renal length was not helpful for distinguishing single from duplex kidneys with no difference in mean renal length. Furthermore, duplex kidneys were the larger kidney in 31% of our cases. The findings of the current study should encourage the urologist to be vigilant when interpreting noncontrast CT in the setting of ureteral colic. Axial or coronal noncontrast CT was at best 70% sensitive for detecting duplex ureters compared with 95% sensitivity for contrast enhanced CT. The superior accuracy of contrast enhanced CT was statistically significant (p ⬍0.01). Furthermore, this study probably overestimates the accuracy of diagnosis using noncontrast CT. The radiologists who participated specialize in genitourinary imaging and focus exclusively on abdominal imaging. We believe that in the real world most radiologists do not focus on the presence or absence of a duplex ureter and they might not recognize asymptomatic patients as frequently as
FIG. 4. Contrast enhanced coronal image of patient with duplex ureter. Second ureter was visualized that was not seen on noncontrast images.
1448
GENITOURINARY IMAGING WITH NONCONTRAST COMPUTERIZED TOMOGRAPHY
do not come to the attention of a urologist. However, given the lifetime prevalence of symptomatic nephrolithiasis (10% of men and 4% of women),10 it is reasonable to assume that urologists who treat a large number of patients with nephrolithiasis will encounter this anatomical variant 1 or more times in their careers. Being mindful of this is helpful in the diagnosis and treatment of these patients.
4.
5.
6.
Abbreviations and Acronyms CT ⫽ computerized tomography NPV ⫽ negative predictive value
7.
8.
REFERENCES 1.
Hartman GW and Hodson CJ: The duplex kidney and related abnormalities. Clin Radiol 1969; 20: 387. 2. Privett JT, Jeans WD and Roylance J: The incidence and importance of renal duplication. Clin Radiol 1976; 27: 521. 3. Mutazindwa T and Husseini T: Imaging in acute renal colic: the intravenous urogram remains the gold standard. Eur J Radiol 1996; 23: 238.
9.
10.
Smith RC, Rosenfield AT, Choe KA, Essenmacher KR, Verga M, Glickman MG et al: Acute flank pain: comparison of non-contrast-enhanced CT and intravenous urography. Radiology 1995; 194: 789. Ripolles T, Agramunt M, Errando J, Martinez MJ, Coronel B and Morales M: Suspected ureteral colic: plain film and sonography vs unenhanced helical CT. A prospective study in 66 patients. Eur Radiol 2004; 14: 129. Chen MY and Zagoria RJ: Can noncontrast helical computed tomography replace intravenous urography for evaluation of patients with acute urinary tract colic? J Emerg Med 1999; 17: 299. Katz DS, Lane MJ and Sommer FG: Unenhanced helical CT of ureteral stones: incidence of associated urinary tract findings. AJR Am J Roentgenol 1996; 166: 1319. Caoili EM, Cohan RH, Korobkin M, Platt JF, Francis IR, Faerber GJ et al: Urinary tract abnormalities: initial experience with multi-detector row CT urography. Radiology 2002; 222: 353. Zissin R, Apter S, Yaffe D, Knots E, Gayer G, Nissenkorn I et al: Renal duplication with associated complications in adults: CT findings in 26 cases. Clin Radiol 2001; 56: 58. Soucie JM, Thun MJ, Coates RJ, McClellan W and Austin H: Demographic and geographic variability of kidney stones in the united states. Kidney Int 1994; 46: 893.