Residents Section Structured Review Article

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1 Residents Section Structured Review rticle O Connor et al. CT Urography Residents Section Structured Review rticle Residents inradiology Owen J. O Connor 1 Michael M. Maher O Connor OJ, Maher MM Keywords: CT urography, hematuria DOI: /JR Received December 30, 2009; accepted after revision February 2, oth authors: Department of Radiology, University College Cork and Cork University Hospital, Wilton, Cork, Ireland. ddress correspondence to M. M. Maher (m.maher@ucc.ie). WE This is a Web exclusive article. JR 2010; 195:W320 W X/10/1955 W320 merican Roentgen Ray Society CT Urography Key Points 1. Standard CT urography consists of unenhanced, nephrographic, and pyelographic phases. 2. CT urography is an excellent technique for the evaluation of urinary tract calculi and renal masses, having high sensitivity and specificity for both conditions because it facilitates multiplanar imaging of the urinary system. 3. Compression, an IV saline bolus, and diuretics have been used to optimize ureteric distention with variable results. 4. Whether CT urography should replace excretory urography in the evaluation of hematuria remains controversial. Definitive resolution of this question is limited by a lack of randomized studies. The European Society of Urogenital Radiology defines CT urography as a diagnostic examination optimized for imaging the kidneys, ureters, and bladder with thin-slice MDCT, IV administration of contrast medium, and image acquisition in the excretory phase [1]. CT urography resembles excretory urography in that the examinations consist of unenhanced, nephrographic, and pyelographic phases [2]. CT urographic protocols are being refined, and efforts are being focused on optimization of radiation exposure and urothelial imaging. This review describes the current status of CT urography as a standalone imaging study in the evaluation of hematuria. Imaging Technique Radiologists have used the imaging techniques of excretory urography to develop CT urographic protocols. typical CT urographic protocol has three phases that allow complete evaluation for the most common urologic causes of hematuria, that is, calculi, renal masses, and urothelial tumors (Fig. 1). fter an initial unenhanced acquisition, nephrographic phase images are acquired seconds after administration of a nonionic contrast agent ( ml of 300 mg I/mL at 2 4 ml/s) [3]. Imaging (2.5- to 5-mm slice thickness) is typically confined to the kidneys during this phase. Nephrographic phase imaging has the highest sensitivity in the detection of renal masses, and correlation with unenhanced images is required to show unequivocal enhancement. Pyelographic phase images are acquired 5 15 minutes after contrast administration to evaluate the urothelium from the kidneys to the bladder (Fig. 2). Imaging Features Skeptics argue that unlike excretory urography, CT does not yield physiologic information based on the degree of delayed excretion, which is considered an index of the severity of obstruction on excretory urograms [2]. CT urography, however, does reliably show signs of obstruction, including hydronephrosis, hydroureter, ipsilateral renal enlargement, perinephric and periureteric fat stranding, perinephric fluid, and ureterovesical edema [3, 4] (Fig. 3). The combination of hydronephrosis, hydroureter, and perinephric stranding has a positive predictive value of 90% for obstruction in the presence of urinary tract calculi [3]. The soft-tissue rim sign is a circumferential rim of soft-tissue attenuation surrounding abdominal or pelvic calcification. This sign is a reliable indicator that the calcification lies in the ureter and thus aids in differentiation of distal ureteric calculus from pelvic phlebolith [5]. CT urographic findings also help predict the likelihood of stone passage in that larger stones are less likely to pass spontaneously. Spontaneous passage rates for ureteric calculi are 76% for calculi 2 4 mm in diameter, 60% for calculi measuring 5 7 mm, 48% for those measuring 7 9 mm, and less than 25% for stones larger than 9 mm [6]. W320 JR:195, November 2010

CT Urography Fig. 1 36-year-old man with right renal colic due to distal ureteric calculus.

, Unenhanced pelvic CT urogram shows calculus (arrow) in region of vesicoureteric junction on right.

4 68 year-old man with transitional cell carcinoma of bladder and congenital absence of left kidney. Heterogeneous lymph node mass is present on right side.

, Nephrographic phase CT urogram shows softtissue mass (arrow) to left of midline near dome of bladder and absence of left kidney. Fig. 2 52-year-old man with renal cysts.

Malignant urologic tumors, such as renal cell carcinoma and transitional cell carcinoma, are potentially detectable during unenhanced imaging examinations.

Possible malignant tumors are further characterized with contrast-enhanced CT urography.

2 CT Urography Fig year-old man with right renal colic due to distal ureteric calculus. Imaging of pelvis was performed with patient prone to ascertain whether stone was in distal ureter or in bladder. ecause of its size (< 3 mm), stone should pass spontaneously., Unenhanced pelvic CT urogram shows calculus (arrow) in region of vesicoureteric junction on right., Sagittal reconstruction of unenhanced CT urogram confirms that calculus (arrowhead) is not in dependent portion of bladder and is therefore in distal ureter, not in bladder. Fig year-old man with transitional cell carcinoma of bladder and congenital absence of left kidney. Heterogeneous lymph node mass is present on right side., CT scan through pelvis shows soft-tissue mass (arrowhead) in bladder that contrasts with lowattenuation urine in bladder., Nephrographic phase CT urogram shows softtissue mass (arrow) to left of midline near dome of bladder and absence of left kidney. Fig year-old man with renal cysts. Coronal reformation of pyelographic phase CT urogram shows multiple bilateral parapelvic renal cysts (arrows). Malignant urologic tumors, such as renal cell carcinoma and transitional cell carcinoma, are potentially detectable during unenhanced imaging examinations. Renal cell carcinoma and transitional cell carcinoma typically appear solid on unenhanced images and have higher attenuation (5 30 HU) than urine [7]. Possible malignant tumors are further characterized with contrast-enhanced CT urography. Malignant renal and urothelial tumors both exhibit early enhancement and washout after IV contrast administration, which assists in characterization [8]. ecause of this property, an enhancing urothelial lesion can be detected in the nephrographic phase, in which urine has low attenuation (Fig. 4). Greater than 10 HU lesion enhancement compared with the findings on unenhanced images indicates the lesion is solid. Greater than 20 HU enhancement strongly suggests the lesion is malignant [9] (Fig. 5). CT urography accurately depicts the location of lesions. Renal cell carcinoma originates in the renal cortex between the corticomedullary junction and the renal periphery (Fig. 6). Transitional cell carcinoma of the kidney is generally seen as a sessile filling defect on pyelographic phase images and may compress and displace the renal sinus fat [7]. lthough advanced transitional cell carcinoma infiltrates the renal parenchyma causing Fig year-old man with obstructing calculus in distal part of left ureter. Coronal reformation of unenhanced CT scan shows hydronephrosis and hydroureter on left. Calculus (arrowhead) is in distal ureter. Extensive streak artifact from left total hip replacement is evident. architectural distortion, the reniform shape is usually maintained, whereas it is not in renal cell carcinoma [7]. Infiltration can cause focal delay of enhancement, but this finding is nonspecific [7]. Foci of necrosis make it difficult to differentiate transitional cell carcinoma from lymphoma, metastatic lesions, and xanthogranulomatous pyelonephritis. Enhancement of ureteric transitional cell carcinoma at the site of ureteric obstruction is best seen in the nephrographic phase and facilitates differentiation from ureteric calculi. dditional features of transitional cell carcinoma of the ureter include wall thickening, stenosis, and infiltration of the fat, which manifests periureteric fat stranding (Fig. 7). JR:195, November 2010 W321

O Connor et al. Fig. 5 74-year-old woman with left-sided renal cell carcinoma., Unenhanced CT scan shows solid left renal lesion (arrow) and expansion of renal contour.

dvantages of CT Urography Three-dimensional reformations with coronal and sagittal maximum intensity projections of the kidneys and urinary collecting systems facilitate thorough examination for

Reports have shown sensitivity ranging from 98% to 100% and specificity of 92 100% for unenhanced CT in the detection of urinary tract calculi [4].

associated with excretory urography is therefore eliminated.

Study results [10] suggest that CT urography has excellent sensitivity (89 100%) and specificity in the detection of pelvicaliceal and ureteric transitional cell carcinoma.

3 O Connor et al. Fig year-old woman with left-sided renal cell carcinoma., Unenhanced CT scan shows solid left renal lesion (arrow) and expansion of renal contour., Nephrographic phase CT scan shows avid peripheral enhancement with central hypoattenuation (arrowhead) suggesting necrosis. dvantages of CT Urography Three-dimensional reformations with coronal and sagittal maximum intensity projections of the kidneys and urinary collecting systems facilitate thorough examination for renal and urothelial malignancy. The advantages of unenhanced CT over excretory urography in the detection of urinary tract calculi are well established. Reports have shown sensitivity ranging from 98% to 100% and specificity of % for unenhanced CT in the detection of urinary tract calculi [4]. Unlike excretory urography, CT for the evaluation of urinary tract calculi (stone protocol) does not require IV contrast administration in most circumstances, and the risk of nephrotoxicity associated with excretory urography is therefore eliminated. It is widely accepted that CT urography outperforms ultrasound, excretory urography, and radiography in the evaluation of renal parenchymal masses and urinary tract calculi. Study results [10] suggest that CT urography has excellent sensitivity (89 100%) and specificity in the detection of pelvicaliceal and ureteric transitional cell carcinoma. Data have prompted investigators in the field to conclude that CT urography is more sensitive and specific than excretory urography in the detection of urothelial tumors. It has been suggested [1] that CT urography be performed as a first-line technique in the evaluation of hematuria when the risk of disease outweighs the risk of radiation exposure, as in the care of patients at high risk of urologic cancer. The debate continues, however systematic review [11] of diagnostic tests and algorithms used for investigating hematuria concluded that the available evidence was insufficient to draw firm conclusions about the diagnostic accuracy of imaging studies in determining the cause of hematuria. Techniques Used to Overcome the Limitations of CT Urography Many variations of the standard CT urographic protocol have been investigated with the goal of reducing radiation exposure and optimizing imaging of the urothelium. Caoili et al. [12] reported radiation doses of msv for four-phase CT urography compared with a mean effective dose of 3.6 msv for excretory urography. Radiation doses can be reduced for the unenhanced component of CT urography because image noise, which increases with radiation dose reduction, is less likely to be a problem because of marked Fig year-old man with renal cell carcinoma. Coronal CT scan shows tumor (arrow) originating in corticomedullary region of kidney and distorting normal contour of kidney. Findings strongly suggest presence of renal cell carcinoma. differences in the attenuation of calculi and surrounding soft tissues. Radiation doses in CT urography can be reduced by limiting the number of imaging phases through the use of dual-energy CT or split-bolus technique [3, 13]. Dual-energy CT obviates an unenhanced phase of imaging because virtual unenhanced CT scans can be postprocessed from a contrast-enhanced study acquired with two tube potentials operating simultaneously [13]. This CT technique has shown great promise for differentiating solid renal masses from hyperdense renal cysts and for determining the composition of renal calculi, which may help guide treatment. Fig year-old man with transitional cell carcinoma of ureter., Coronal reformation of unenhanced CT urogram shows soft-tissue thickening (arrow) of left mid ureter, proximal hydroureter, and hydronephrosis of small atrophic kidney., xial pyelographic phase CT image shows increased soft-tissue thickening and expansion of left ureter with stranding of periureteric fat (arrowhead). Right ureter (arrow) is normal. W322 JR:195, November 2010

CT Urography Fig. 8 45-year-old man with normal findings.

before acquisition in nephrographic phase, which included second injection of IV contrast material.

administration of 30 50 ml of contrast material, and a second bolus of 80 100 ml of IV contrast material is given after an 8- to 10-minute

Thus in a single nephropyelographic phase acquisition, the renal parenchyma (nephrographic phase) and the collecting system, ureters, and

possible disadvantage of the split-bolus technique is that the presence of contrast material within the ureter at imaging can obscure the

Detection of urothelial tumors is widely believed to rely on optimal distention and opacification of the ureters and pelvicaliceal Fig.

, Ultrasound image shows asymmetric thickening (arrow) of wall of bladder.

4 CT Urography Fig year-old man with normal findings. CT urogram obtained with split-bolus technique shows collecting systems opacified by administration of small volume of IV contrast material before acquisition in nephrographic phase, which included second injection of IV contrast material. Radiation doses can be reduced with use of a split-bolus (two-phase) technique in which an unenhanced acquisition is followed by IV administration of ml of contrast material, and a second bolus of ml of IV contrast material is given after an 8- to 10-minute delay, during which the acquisition is performed [3] (Fig. 8). Thus in a single nephropyelographic phase acquisition, the renal parenchyma (nephrographic phase) and the collecting system, ureters, and bladder (pyelographic phase) are assessed in a reduced the number of phases at a reduced radiation dose. possible disadvantage of the split-bolus technique is that the presence of contrast material within the ureter at imaging can obscure the subtle isoattenuating tumors that are not seen in the low-dose unenhanced phase (Fig. 9). Detection of urothelial tumors is widely believed to rely on optimal distention and opacification of the ureters and pelvicaliceal Fig year-old man with hematuria due to transitional cell carcinoma of bladder with ureteric extension., Ultrasound image shows asymmetric thickening (arrow) of wall of bladder., Excretory urogram shows large filling defect (arrowhead) in bladder that may be explained by blood clot. C, Unenhanced CT scan shows focal thickening (arrow) of bladder wall. D, CT scan shows extension of soft tissue from bladder into distal ureter (arrowhead) at vesicoureteric junction. E, Pyelographic phase CT scan shows tumor (arrow) is not apparent owing to presence of contrast material in bladder. F, Three-dimensional reformation confirms presence of tumor (arrowhead) in distal ureter and shows ipsilateral hydronephrosis. C D E F JR:195, November 2010 W323

5 O Connor et al. system. Complete bilateral distention of the ureters can be difficult to achieve owing to peristaltic contractions [9]. Oral hydration with 1 L of water minutes before CT urography can improve delineation of the ureters by promoting diuresis [14]. Water has the additional benefit of serving as a negative contrast agent in the gastrointestinal tract. It has been suggested [15] that prone imaging improves ureteric distention and opacification, but the prone position can be uncomfortable, and the benefits of prone imaging are disputed. Imaging in the prone position is used, however, to discriminate free intravesical stones and those impacted at the ureterovesical junction. Compression, saline infusion, and diuretics also have been investigated for optimizing ureteric imaging. Compression can increase proximal ureteric distention and can be released for imaging of the distal ureters. Compression techniques, however, require additional imaging and increase radiation exposure. Even with compression, 25% of ureteric segments are not visualized, which is not significantly different from the results with CT urography without compression [16]. The benefits of saline infusion are debated because studies have yielded conflicting results [12, 15]. uthors have suggested that saline infusion occasionally stimulates peristalsis, which can have a deleterious effect on CT urography [15]. ecause of these limitations, the European Society of Urogenital Radiology [1] does not advocate routine use of saline infusion. In a review, Silverman et al. [9], however, conclude that despite the potential limitations, saline infusion is safe, inexpensive, and easy to incorporate into the CT urographic protocol. dministration of a low dose of diuretic (furosemide 0.1 mg/kg to a maximum of 10 mg) 1 minute before CT urography improves mid and distal ureteric opacification and distention compared with that achieved with saline infusion alone [9]. This technique decreases attenuation in the ureters and reduces the time delay for pyelographic imaging but is not suitable for all patients [1]. disadvantage of CT urography compared with excretory urography is encountered in imaging of patients with asymmetric excretion, particularly those with unilateral obstruction. In these patients, the lack of sequential imaging with CT urography can result in suboptimal opacification in the pyelographic phase on the obstructed side. Many experts agree that regardless of the CT urographic protocol used, there will always be ureteric segments that are suboptimally opacified and distended [5]. There are concerns that urothelial lesions in unopacified segments might be missed because of these deficiencies [2]. This view, however, is not universally held; some investigators have found that urothelial neoplasms almost always manifest filling defects or obstruction [10]. Tsili et al. [10] found that the finding of a nonopacified ureter had a negative predictive value of 100% for the presence of urothelial lesions. Conclusion MDCT is the most sensitive and specific test for the diagnosis of urinary tract calculi and for detecting and characterizing renal masses [2]. The universal acceptance of CT urography as a one-stop imaging examination in the investigation of hematuria is prevented by the scarcity of evidence (lack of randomized controlled studies and meta-analyses) to support a view that CT urography is as accurate as excretory urography in the evaluation of urothelium. In addition, results of economic analyses suggest that it may be costeffective to use ultrasound to evaluate persistent hematuria and to perform CT urography only if the ultrasound results are normal [11]. Many radiologists believe that the additional radiation exposure in CT urography has replaced concerns regarding sensitivity in the detection of urothelial tumors as the major obstacle to replacing excretory urography with CT urography. The merican College of Radiology [17] considers CT urography highly recommended for the investigation of hematuria. Split-bolus and low-dose imaging techniques are potentially effective methods of radiation dose reduction that may strengthen the argument for the use of CT urography in place of excretory urography. References 1. Van der Molen J, Cowan NC, Mueller-Lisse UG, Nolte-Emsting CC, Takahashi S, Cohan RH; CT Urography Working Group of the European Society of Urogenital Radiology (ESUR). CT urography: definition, indications and techniques a guideline for clinical practice. Eur Radiol 2008; 18: Nolte-Ernsting C, Cowan N. Understanding multislice CT urography techniques: many roads lead to Rome. Eur Radiol 2006; 16: O Connor OJ, McSweeney SE, Maher MM. Imaging of hematuria. Radiol Clin N m 2008; 46: Fielding JR, Silverman SG, Rubin GD. Helical CT of the urinary tract. JR 1999; 172: Kawashima, Sandler CM, oridy IC, Takahashi N, enson GS, Goldman SM. Unenhanced helical CT of ureterolithiasis: value of the tissue rim sign. JR 1997; 168: Coll DM, Varanelli MJ, Smith RC. Relationship of spontaneous passage of ureteral calculi to stone size and location as revealed by unenhanced helical CT. JR 2002; 178: rowne RF, Meehan CP, Colville J, Power R, Torreggiani WC. Transitional cell carcinoma of the upper urinary tract: spectrum of imaging findings. RadioGraphics 2005; 25: Lang EK, Macchia RJ, Thomas R, et al. Improved detection of renal pathologic features on multiphasic helical CT compared with IVU in patients presenting with microscopic hematuria. Urology 2003; 61: Silverman SG, Leyendecker JR, mis ES Jr. What is the current role of CT urography and MR urography in the evaluation of the urinary tract? Radiology 2009; 250: Tsili C, Efremidis SC, Kalef-Ezra J, et al. Multidetector row CT urography on a 16-row CT scanner in the evaluation of urothelial tumors. Eur Radiol 2007; 17: Rodgers M, Nixon J, Hempel S, et al. Diagnostic tests and algorithms used in the investigation of hematuria: systematic reviews and economic evaluation. Health Technol ssess 2006; 10:10, iii iv, xi Caoili EM, Inampudi P, Cohan RH, Ellis JH. Optimization of multi-detector row CT urography: effect of compression, saline administration, and prolongation of acquisition delay. Radiology 2005; 235: Graser, Johnson TR, Chandarana H, Macari M. Dual energy CT: preliminary observations and potential clinical applications in the abdomen. Eur Radiol 2009; 19: Kawamoto S, Horton KM, Fishman EK. Opacification of the collecting system and ureters on excretory-phase CT using oral water as contrast medium. JR 2006; 186: Sanyal R, Deshmukh, Sheorain V, Taori KC. Urography: a comparison of strategies of upper urinary tract opacification. Eur Radiol 2006; 17: Sudakoff GS, Dunn DP, Hellman RS, et al. Opacification of the genitourinary collecting system during MDCT urography with enhanced CT digital radiography: nonsaline versus saline bolus. JR 2006; 186: Choyke PL, luth EI, ush WH Jr, et al.; Expert Panel on Urologic Imaging. Hematuria. Reston, V: merican College of Radiology, 2005; www. guideline.gov/summary/summary.aspx?doc_ id= ccessed January 12, 2010 W324 JR:195, November 2010

UROGENITAL. Abstract Objective To assess the effect of oral hydration and contrastmedium

UROGENITAL. Abstract Objective To assess the effect of oral hydration and contrastmedium Eur Radiol DOI 10.1007/s00330-010-1785-8 UROGENITAL Dieter H. Szolar Manfred Tillich Klaus W. Preidler Multi-detector CT urography: effect of oral hydration and contrast medium volume on renal parenchymal