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Computed Tomographic Urography Update: An Evolving Urinary Tract Imaging Modality
Computed Tomographic Urography Update: An Evolving Urinary Tract Imaging Modality Zachary W. Washburn, MD, Jonathan R. Dillman, MD, Richard H. Cohan, MD, Elaine M. Caoili, MD, MS, and James H. Ellis, MD Multi-detector computed tomography urography (CTU) is now well established as the imaging modality of choice for comprehensive evaluation of the kidneys and urinary tract, having largely replaced excretory urography. Over the past decade, CTU techniques have continued to evolve with the goal of improving urothelial surface visualization. Numerous benign and malignant conditions of the kidneys, ureters, and urinary bladder can be accurately depicted by CTU. This article provides a contemporary review of CTU imaging protocols, image postprocessing techniques, appearances of various urinary tract pathologic conditions, and pitfalls in image interpretation. Semin Ultrasound CT MRI 30:233-245 © 2009 Elsevier Inc. All rights reserved.
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ver the past decade, multidetector computed tomography urography (CTU) has become the imaging modality of choice for comprehensive evaluation of the kidneys and urinary tract. To distinguish CTU from other CT techniques (for example, protocols tailored to evaluate for urolithiasis or renal masses), a recently proposed definition stated that CTU should be optimized for evaluation of the urinary tract and must include excretory phase imaging.1 A combination of unenhanced CT imaging to evaluate for urolithiasis and to provide a baseline image to characterize masses, nephrographic phase imaging to evaluate for benign and malignant renal parenchymal processes, and excretory phase imaging to evaluate for abnormalities of the urothelium, CTU has largely replaced excretory urography (EU). Much recent effort has been aimed at optimizing excretory phase urinary tract distension and opacification with the hope that greater separation of the urothelial surfaces and outlining the entire urothelium with excreted contrast would provide a more detailed evaluation of urothelium, enhancing the sensitivity for lesion detection. In addition, recent effort has gone into reducing patient radiation exposure related to CTU, as this imaging technique has been associated with relatively high radiation doses when compared with EU.1-7 Several authors have advocated the use of tailored CTU protocols rather than a “onesize-fits-all” approach.1,2 For example, radiation exposure University of Michigan Health System, Department of Radiology, C.S. Mott Children’s Hospital, Ann Arbor, MI. Address reprint requests to Jonathan R. Dillman, MD, University of Michigan Health System, Department of Radiology, C.S. Mott Children’s Hospital, F3503, 1500 E. Medical Center Dr., Ann Arbor, MI 48109-5252. E-mail: [email protected]
0887-2171/09/$-see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1053/j.sult.2009.03.005
can be reduced by eliminating certain imaging phases based on the specific clinical question and patient risk factors. CTU is most commonly performed for the evaluation of hematuria, especially in patients at increased risk of urothelial malignancy. Other indications include evaluation of urinary tract obstruction (including hydronephrosis and hydroureter of uncertain etiology), assessment of urinary diversion integrity after cystectomy, assessment of urinary tract trauma (including iatrogenic), evaluation of complicated infections (including fungal infections and tuberculosis), and determination of anatomy before difficult percutaneous nephrolithotomy cases. It is clear from this list of indications that CTU is effective at detecting many benign and malignant renal and urinary tract conditions.
Techniques Contrast Material Administration Single-Bolus Technique The original CTU technique, still in use today, calls for 3 imaging phases and uses a single intravenous bolus injection of contrast material.3 An unenhanced phase is initially performed to evaluate patients for urinary calculi, to establish a baseline for assessment of any subsequently detected lesion enhancement, and to assist in the characterization of certain masses, such fat-containing angiomyolipomas, where noncontrast images may more clearly depict tissue attenuation characteristics. Following contrast material administration, 2 additional phases are obtained. Nephrographic phase imaging is performed approximately 100-120 seconds after the initiation of contrast material injection to evaluate the en233
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234 hancement characteristics of renal parenchymal lesions, while excretory phase imaging is performed after a much greater time delay (to allow for ample urinary tract opacification) to assess the urothelium. Advantages of this technique include its ease of contrast material administration and the complete evaluation of the kidneys and urinary tract it affords. Its primary disadvantage is the relatively high patient radiation exposure due to 3 separate imaging phases. Double-Bolus Technique As its name implies, the double-bolus CTU technique relies on 2 separate administrations of intravenous contrast material separated by a specific amount of time.8,9 This technique allows for the acquisition of a combined nephrographic-excretory imaging phase following unenhanced imaging. The double-bolus approach has several advantages over the single-bolus technique, including decreased patient radiation dose (because only 1 series of enhanced images is obtained), fewer images to archive, and fewer images to review. A theoretic disadvantage of this technique is that it may produce less urinary tract distension when compared with the singlebolus technique (because only the first of the 2 administered boluses opacifies the urinary tract and contributes to contrast-induced diuresis at the time of image acquisition). Dillman et al10 showed that the only significant differences in distension between the 2 techniques occurred at the level of the renal collecting systems (and not the ureters). Another concern regarding this technique is the theoretic risk that renal collecting system urothelial lesions might be obscured on combined nephrographic-excretory phase images due to adjacent renal enhancement.2 Despite these concerns, Chow et al11 reported high sensitivity and specificity (100% and 99%, respectively) for detection of urothelial tumors in the renal collecting systems and renal pelvises using this method. Triple-Bolus Technique Kekelidze et al12 described a novel CTU technique that combines arterial, nephrogenic, and excretory phase information into a single imaging acquisition. This technique requires the intravenous administration of 3 separate boluses of contrast material, each separated by a specific amount of time, before a single acquired contrast-enhanced series of images. Triplebolus CTU allows for the anatomic evaluation of renal arterial vasculature, including the number and course of the renal arteries, without the additional patient radiation dose of a separate arterial imaging phase acquisition. The advantages and disadvantages of this technique are generally similar to those of the double-bolus technique; however, for any given contrast dose, the total volume of contrast material opacifying the renal parenchyma and excreted into the renal collecting systems will be even smaller (because the total dose must now be split into 3 boluses), with the theoretic risk of compromising assessment of renal masses and urothelial lesions. This technique has not gained widespread acceptance, likely due to a combination of protocol complexity and the fact that in most patients referred for CTU (with hematuria and/or suspected urothelial lesions, for example), there is little interest in assessing them for renal artery pathology. This tech-
nique may be useful, however, in the evaluation of potential living renal donors.
Ancillary Maneuvers Patient Positioning The use of prone positioning during excretory phase imaging has shown mixed results when evaluated for its effects on urinary tract opacification. Most investigators perform CTU with the patient in the supine position. Prone positioning for CTU was initially thought to favorably affect urinary tract opacification,3 but it has since been shown to be of little benefit, especially when compared with other ancillary techniques.13,14 However, prone positioning may occasionally be useful in some patients. For example, it can be employed to distinguish dependent bladder calculi from impacted ureterovesical junction calculi at unenhanced imaging.2 Several maneuvers have been recommended to facilitate the mixing of excreted contrast and urine in the bladder or any dilated portions of the renal collecting systems and ureters to obtain more homogeneous urinary tract opacification and avoid fluid-fluid (contrast-urine) levels. Such homogeneous opacification may improve sensitivity in the detection of urothelial lesions, especially in the bladder. Uniform opacification has been obtained in a variety of ways, including asking patients to void before the beginning of the examination (without moving or turning the patient), turning (or “log rolling”) the patient on the CT scanner, and even having the patient get off the CT scanner table and walk around the CT room before excretory phase image acquisition.15 While “log-rolling” maneuvers may have no effect on opacification of normal ureters;15 this technique has been used to improve opacification of dilated collecting systems.16 Oral Hydration Positive enteric contrast material is not used with CTU, because it can interfere with the identification of the contrast opacified mid and distal ureters as well as compromise the quality of subsequently created 3-dimensional (3D) reconstructed images. Oral administration of up to 1000 mL of water 20-60 minutes before excretory phase imaging may be useful, as it acts both as a negative contrast agent within bowel and as a means of patient hydration, thereby potentially improving distension of ureteral segments due to resulting increased diuresis.17 Urinary tract opacification may also be improved after oral hydration. Such opacification has been found to be greatest if water is ingested 60 minutes rather than 15-20 minutes before excretory phase imaging.17,18 When furosemide is also used, oral hydration with water can lessen any risk of dehydration. Abdominal Compression External abdominal compression, which has been used for years during EU, has also been used during CTU. It has been presumed that abdominal compression would improve renal collecting system and proximal ureteral distension and opacification when it is applied, and that distension and opacification of the mid and distal ureters would be improved upon compression release. Initial studies using this
Computed tomographic urography update technique reported improved opacification of the ureters.3,8 However, Caoili et al19 found no significant improvement in urinary tract distension when using abdominal compression; furthermore, urinary tract opacification was improved more using intravenous hydration and delayed acquisition timing than by abdominal compression. From a practical standpoint, compression bands are cumbersome to apply, somewhat uncomfortable for the patient, and demanding of technologists’ time. Abdominal compression is also contraindicated in certain patients, including those with recent abdominal or pelvic surgery, abdominal aortic aneurysm, and acute urinary tract obstruction. For these reasons, the use of external abdominal compression bands during CTU has largely been abandoned in favor of other ancillary maneuvers. Intravenous Hydration Intravenous hydration before CTU image acquisition using normal (0.9%) saline has been used to improve image quality with mixed results. Expansion of the intravascular volume with this technique was expected to enhance diuresis and augment urinary tract opacification and distension. Using a 250 mL intravenous bolus, Caoili et al19 reported a small, but significant, improvement of urinary tract opacification and distension. McTavish et al,13 using a similar technique, also reported improved urinary tract opacification. Conversely, Sudakoff et al20 found no additional benefit in urinary tract opacification with an intravenous saline bolus, while Silverman et al21 found that there was no additional benefit to a saline infusion when intravenous furosemide was administered. Most researchers have found that an intravenous saline bolus is well-tolerated by nearly all patients, although particular care should be taken when hydrating volume-sensitive patients (for example, individuals with congestive heart failure). At the present time, despite its only mild efficacy, this technique is still used widely. Furosemide Low-dose intravenous furosemide (usually at doses of between 5 and 20 mg) has been used to augment urinary tract distension and opacification. Using a 10 mg dose, Sanyal et al14 found that the distal ureters could be opacified in 93% of cases, which represented improved opacification when compared with imaging performed without a diuretic. Other authors have reported similar findings using 20 mg furosemide.22,23 Multiple authors have reported that superior urinary tract opacification could be obtained with furosemide compared to saline infusion alone.14,21,24 Another potential advantage of a diuretic is the diminished concentration of the excreted contrast material in the renal collecting systems and ureters that it produces. Such diminished concentration may allow for detection of high-attenuation calculi in the urinary tract even on excretory phase images and also might reduce possible streak artifacts that could obscure visualization of small urothelial lesions.24 While low-dose diuretics are generally safe and well-tolerated by most patients, some precautions are needed if furosemide is to be used. This medication is contraindicated in patients with sulfa drug allergies. In addition, it should be
235 used with caution in patients with hypokalemia, hypotension, dehydration, acute renal failure, acute ureteral obstruction, anuria, as well as in those receiving certain medications, such as ototoxic agents.
Excretory Phase Imaging Delay Time Traditionally, CTU has been performed using a fixed excretory phase delay time. The ideal delay time should allow for complete opacification of the renal collecting systems, ureters, and bladder. Reliable opacification of the mid and distal ureteral segments has proven to be one of the greatest challenges in CTU. While McNicholas et al3 used a fixed excretory delay time of 10 minutes (600 s), a wide range of delay times (ranging from 3 to 15 min) have been proposed. This variation may be, at least in part, due to other differences in CTU protocols and ancillary maneuvers employed. For example, the optimal excretory delay time is shortened when using furosemide compared with imaging performed without furosemide.25 In a protocol using intravenous saline hydration, Caoili et al19 found that an imaging delay of 450 seconds improved distension of the upper urinary tract compared with a delay of 300 seconds. Meindl et al,26 also using a protocol with intravenous saline hydration, reported that a more prolonged delay of 10-16 minutes (median, 11 min) improved opacification of the distal ureter without having an adverse impact on opacification of the proximal ureter and renal collecting system. Using a similar protocol, the same investigators analyzed the value of performing both early (median 11 min) and late (median, 16 min) excretory phase imaging and found no significant difference in opacification between these 2 delay times.27 In a protocol using low-dose furosemide, Kemper et al25 individualized excretory phase delay time using periodic “low-dose test scans” through the distal ureters. They found that the median time delay required for maximal urinary tract opacification was 420 seconds (with a standard deviation of 121 s) in patients with normal renal function. Only 7.8% of distal ureters were not opacified using this method. In the same study, the difficult challenge of timing excretory phase imaging in the setting of urinary tract obstruction was also addressed. In patients with unilateral ureteral obstruction, the range of time to opacification of the affected ureter was 10-33 minutes.25
Image Postprocessing and Viewing Current generation multidetector helical CT scanners allow for the acquisition of volumetric data. Such data can be used to generate both submillimeter axial images and thicker reconstructed axial sections with increased signal-to-noise ratio. At our institution, using a 64-channel multidetector CT scanner, excretory-phase images are acquired using 32 ⫻ 1.25 mm collimation. The 1.25-mm source axial images are then used to reconstruct a separate imaging series with 2.5-mm images with 1.25 mm of section overlap. The thicker images are typically reviewed, with the source data used only to create the 2-dimensional reformatted and 3D recon-
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Z.W. Washburn et al Curved-planar reformatted (CPR) images depict a large portion of the urinary tract on a single image (as opposed to MPR images that display smaller portions of the urinary tract on a single image due to structures moving into or out of the plane of reformation).8,21 Potential drawbacks to this form of image reformation include the increased time needed to create the images on a 3D workstation and the potential for
Figure 1 Urothelial polyp. Eighty-nine-year-old man with a history of bladder cancer undergoing routine follow-up double-bolus CTU examination. Axial CTU image (A) viewed with a wide window/level setting demonstrates a small filling defect (arrow) in the right renal collecting system that proved to be a urothelial polyp after endoscopic biopsy. The same level (B) viewed with a narrow window/ level setting shows how a small filling defect can be missed (arrow) if the urothelium is not evaluated using appropriate window/level settings.
structed images. The urothelium should be evaluated using wide window/level settings (often similar to those used to view the skeleton) to avoid missing subtle urothelial abnormalities that may be obscured by adjacent hyperattenuating contrast material (Fig. 1). Volumetric source data allow for the creation of isotropic 2-dimensional reformatted images in any plane as well as a variety of forms of 3D image reconstruction. Coronal and sagittal multi-planar reformatted (MPR) images (including oblique reformations) are particularly useful for characterizing urinary tract pathology. This is due to the craniocaudal orientation of the urinary tract and the superior ability of multiplanar reformations to depict structures that traverse the z-axis.
Figure 2 Horseshoe kidney. Forty-one-year-old man undergoing double-bolus CTU examination for evaluation of microscopic hematuria. Volume-rendered image viewed anteriorly (A) displays midline lower pole renal fusion. An enhancing parenchymal isthmus (arrow) was located below the inferior mesenteric artery (with the latter seen on the axial images). Axial CTU image (B) reveals normal caliber ureters coursing anterior to lower moiety renal parenchyma (arrows).
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Figure 3 Duplicated urinary tract with ureterocele. Fifty-nine-yearold woman with chronic right flank pain undergoing double-bolus CTU for evaluation of right-sided pelvicaliectasis demonstrated at ultrasound. Volume-rendered image viewed anteriorly (A) demonstrates a duplicated right renal collecting system and ureter. There is mild dilatation of both the upper and the lower moiety renal collecting systems and ureters. The upper moiety ureter inserted just inferior to the insertion of the lower moiety ureter (not shown). Coronal reformatted (B) and axial (C) images demonstrate the right upper moiety ureter terminating in a ureterocele (white arrows). Orthotopic insertion of the unduplicated left ureter is also visible (black arrow).
distortion of anatomy and pathology due to the reformatting process itself. Dillman et al28 recently demonstrated similar sensitivities for axial, coronal reformatted, and CPR images in the retrospective detection of upper tract urothelial neoplasms, although the sensitivity for detecting these neoplasms increased significantly when axial, MPR, and CPR images were used in combination. Use of maximum-intensity projection and average-intensity projection images was first described for use with CTU by McNicholas et al.3 These 3D reconstruction techniques are used to display the entire volumetric data set on a single image or multiple images (depending on slab thickness). Such images are most commonly displayed in the coronal plane and appear somewhat similar to traditional EU images. While maximum-intensity projection and average-intensity projection images may lack sufficient detail to diagnose certain urothelial abnormalities, such as small filling defects and areas of subtle wall thickening, they do provide a useful format to display and evaluate urinary tract anatomy.
The volumetric data set can also be used to generate 3D volume-rendered (VR) images of the kidneys and urinary tract.4 VR images provide a 3D representation of the kidneys and opacified portions of the upper urinary tract and urinary bladder (or postsurgical urinary reservoir) and can be rotated and viewed in any plane. The diagnostic accuracy in detecting small urothelial lesions is very limited for this type of image reconstruction as only the luminal surface is displayed. For example, in 1 review of CTU examinations performed in patients with known urothelial neoplasms, only 25% could be detected using VR images.6 Furthermore, renal parenchymal lesions can only be detected reliably on VR images when they are large enough to distort the renal contour or when they protrude from the renal surface. When using double-bolus CTU technique, it may be difficult to discriminate the opacified urinary tract from briskly enhancing adjacent renal parenchyma.2 The VR reconstruction technique can be convenient for displaying complicated renal and urinary tract anatomy in a single image (Figs. 2 and 3); however, the diagnostic utility of these VR reconstructions is often limited.
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Imaging of Developmental Anatomic Variants Renal and urinary tract developmental anatomic variants, as well as their potential complications, can be evaluated with CTU. Renal ectopia (including crossed renal ectopia), horseshoe kidney, and renal agenesis are all straightforwardly diagnosed by CTU (Fig. 2).4,8 Urinary tract duplication also is usually easily detected by CTU and should be a diagnostic consideration in the setting of isolated superior pole renal collecting system dilatation.4,8 When duplication is present, CTU can define the exact site of the typically ectopic upper moiety ureter insertion as well as evaluate for the presence of a ureterocele. On CTU, ureteroceles may appear as a round or oval filling defect within the urinary bladder at or near the site of ureter insertion. The ureterocele may contain either central low or high attenuation depending on whether it contains excreted contrast material at the time that it is imaged (Fig. 3). Ectopic ureteral insertions and ureteroceles are rarely detected in the setting of a nonduplicated upper urinary tract. CTU (particularly when using the triple-bolus technique) can be useful in the evaluation of ureteropelvic junction obstruction and assessment of potential living renal donors. CTU can determine which ureteropelvic junction obstructions are due to an extrinsic cause, such as an aberrant renal artery or crossing vein.29 Similarly, CTU may play an important role in the preoperative evaluation of potential living renal donors. In addition to assessing patients for unknown renal and urinary tract pathology, CTU may influence surgical decision-making by providing important anatomic knowledge about the renal vasculature (including the number and course of the renal arteries and veins) and the urinary tract. The anatomic information provided on CTU can be used to determine which kidney will be chosen for donor nephrectomy.30
Imaging of the Postsurgical Urinary Tract CTU can be a useful problem-solving tool in the evaluation of numerous postoperative complications following urinary tract surgery, especially in of the setting of urinary tract diversion with complicated neobladder reconstruction. Postoperative complications that may be diagnosed and characterized by CTU include urinary tract obstruction, ureteral kinks or strictures, anastomotic leaks, and postoperative fluid collections.31
Figure 4 Renal tubular ectasia (medullary sponge kidney). Seventyseven-year-old man with history of bladder cancer undergoing routine follow-up double-bolus CTU examination. Axial (A) and coronal subvolume maximum intensity projection (MIP) (B) images demonstrate numerous abnormal collections of contrast material within the renal medullae that have a “brush-like” appearance (arrows).
Imaging of Benign Acquired Renal and Urinary Tract Conditions Examples of acquired benign renal and urinary tract conditions that can be evaluated with CTU include renal tubular ectasia (medullary sponge kidney), renal papillary necrosis, and pyeloureteritis/cystitis cystica. Renal tubular ectasia is due to abnormal medullary collecting tubule dilatation. The appearance of renal tubular ectasia on CTU and EU are similar (Fig. 4),8 with the abnormal linear collections of contrast material identified within the renal medulla classically described as having a “brush-like” appearance. CTU findings that suggest renal papillary necrosis include renal papillary hypoenhancement (suggesting impaired perfu-
sion) and abnormal contrast-filled cavities in the renal medulla located just peripheral to the calyces. Occasionally, a sloughed renal papilla may present as a urinary tract filling defect (Fig. 5A) and be difficult to differentiate from other abnormalities, including urothelial neoplasm. Additional findings that may be observed in the setting of longstanding renal papillary necrosis include club-shaped minor calyces, rim-like medullary calcifications, and cortical atrophy (Fig. 5B).32,33 In pyeloureteritis cystica and cystitis cystica, numerous tiny suburothelial cystic structures are formed in response to chronic inflammation (most commonly secondary to recurrent urolithi-
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Imaging of Urinary Tract Malignancy Urothelial neoplasms, predominantly of the transitional cell type, are the most common malignancies to affect the upper urinary tract and urinary bladder. Like most carcinomas, these neoplasms are initially noninvasive with prognosis significantly worsening following invasion of tumor into the underlying muscularis propria.35 Therefore, diagnosis of these neoplasms at an early stage is of the utmost importance. Urothelial neoplasms are most commonly solitary, but a large number of individuals develop either synchronous or metachronous lesions (Fig. 7). As a result, complete urinary tract evaluation is necessary at the time of diagnosis as well as when follow-up imaging is performed. Because patients with
Figure 5 Renal papillary necrosis. Thirty-one-year-old man undergoing double-bolus CTU for new-onset gross hematuria and history of heavy nonsteroidal anti-inflammatory drug use. Coronal reformatted image (A) demonstrates a filling defect (arrows) within the left upper pole renal collecting system, which proved to be a sloughed renal papilla at endoscopy. Coronal reformatted image (B) from a 54-year-old woman with a history of bladder cancer demonstrates a collection of contrast material extending from renal collecting system into adjacent medulla (black arrow) and a blunted calyx (white arrow) with thinning of the overlying cortex, changes consistent with papillary necrosis.
asis or infection). These entities can be detected on CTU and usually present as multiple, tiny mural-based filling defects. Benign urinary tract masses can also be detected with CTU. Ureteral fibroepithelial polyps are rare benign urothelial proliferative lesions that usually produce long slender urinary tract filling defects. The point of attachment of these structures to the ureteral wall can often be visualized.34 These lesions often have a strongly suggestive imaging appearance. Urothelial polyps (Fig. 1) and papillomas (Fig. 6) can also be detected and produce urinary tract filling defects, which cannot be differentiated from urothelial malignancy by their CTU appearance.
Figure 6 Urothelial papilloma vs. low-grade urothelial neoplasm. Fifty-nine-year-old woman undergoing double-bolus CTU for right flank pain. Axial image (A) demonstrates a filling defect (arrows) in the right upper pole renal collecting system, pathologically proven to be a urothelial papilloma. Axial image (B) from a 69-year-old man undergoing double-bolus CTU for the evaluation of gross hematuria demonstrates a similar-appearing right upper pole renal collecting system filling defect (arrows), pathologically proven to be a malignant low-grade noninvasive urothelial neoplasm.
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Figure 7 Upper urinary tract urothelial neoplasm. Curved-planar reformatted CTU image (A) demonstrates multiple polypoid filling defects (arrows) within the left renal pelvis and ureter in an 89year-old woman with known multifocal urothelial neoplasm and hematuria. A simple cyst (labeled C) is present within the upper pole of the left kidney. Coronal reformatted image (B) from a 63year-old woman with hematuria demonstrates a small polypoid filling defect (arrowhead) within the distal right ureter that proved to be a malignant low-grade noninvasive urothelial neoplasm. Axial image (C) from a 47-year-old man with hematuria demonstrates circumferential thickening (arrows) of the right ureter that proved to be high-grade noninvasive urothelial neoplasm with flat architecture.
urothelial malignancies are felt to have “at-risk” urothelium, they will usually have extensive follow-up after diagnosis, even in cases where noninvasive tumors are removed in their entirety by transurethral resection. Reliable detection of urothelial neoplasms by CTU has been demonstrated in multiple small series.6,11,28,36,37 At CTU, many upper urinary tract neoplasms present as single or multiple irregular filling defects (Figs. 6 and 7), similar to their classically described appearance at EU.28 Large urothelial neoplasms may also present as a focal mass. However, other appearances have been described. In a study by Caoili et al, just over 50% of upper tract neoplasms produced focal
circumferential wall thickening (Fig. 7).6 In some of these cases, the thickening did not produce urinary tract narrowing or irregularity, indicating that these neoplasms likely could not be detected with EU. At CTU, urinary bladder urothelial neoplasms present similarly to upper tract malignancies, appearing as focal wall thickening (Fig. 8A), intraluminal filling defects (Fig. 8B), or large masses (Fig. 8C). CTU has recently played an increasing role in the detection of bladder urothelial neoplasms, a role traditionally held by cystoscopy. Turney et al38 found CTU to have high sensitivity (93%) and specificity (99%) in detecting bladder cancer when compared to cystoscopy in evaluating
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Figure 8 Bladder urothelial neoplasm. Axial CTU image (A) from a 59-year-old man with hematuria reveals focal left posterior urinary bladder wall urothelial thickening (arrows), proven to be highgrade invasive urothelial neoplasm. Axial image (B) from a 63-yearold man with hematuria shows 2 polypoid filling defects (arrows) within the urinary bladder, proven to be high-grade invasive urothelial neoplasms. Sagittal reformatted image (C) from a 75year-old man with hematuria reveals a large, lobulated, partially calcified mass (arrows) extending through the anterior urinary bladder (arrowheads), proven to be high-grade invasive urothelial neoplasm.
patients greater than 40 years of age with hematuria. Similarly, Knox et al39 found CTU to be highly sensitive (90%) and specific (97%) in a study using cystoscopy with pathologic confirmation as the gold standard. Another study by Shadow et al40 determined that CTU has a high negativepredictive value (95%) in the evaluation of bladder cancers and suggested that further evaluation with cystoscopy may not be needed in certain low-risk patients with negative imaging. We believe that CTU cannot be considered a sufficient substitute for cystoscopy because small and flat tumors remain extremely difficult or even impossible to detect by imaging; however, CTU may be the first study to identify a bladder neoplasm. Furthermore, in a few instances, CTU has detected bladder neoplasms that were missed during cystoscopy.38 Both CTU and cystoscopy have difficulty in the evaluation of bladders in patients who have previously been treated for noninvasive bladder cancers. This is because the bladder wall may become inflamed and scarred following transurethral resection, intravesical immunotherapy, or chemotherapy. In these instances, the 2 studies may play a complementary role in evaluating the bladder.
Incidental Findings Owing to the ability to evaluate other intra-abdominal organs, CTU frequently detects findings outside of the urinary tract. Lui et al41 found incidental extraurinary tract findings to be present in 75.3% of CTU cases performed for the evaluation of hematuria, although only 12.5% were considered highly clinically significant (ie, requiring additional imaging workup or clinical intervention). The most common findings in this category were indeterminate lung nodules and enlarged abdominal lymph nodes. Despite this high prevalence of incidental findings, the extra costs created by additional imaging evaluation of these unexpected unrelated findings was less than $50 per CTU examination performed.
Pitfalls in CTU Interpretation Nonneoplastic and Apparent Filling Defects A variety of benign conditions can cause single or multiple urinary tract intraluminal filling defects that may mimic neoplasm. Blood clots, sloughed renal papillae (Fig. 5), mycetomata (fungus balls), and the exceedingly rare low-attenuation urinary calculus may present as solitary or multiple filling defects within the renal collecting systems, ureters, or
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Z.W. Washburn et al etiology. Benign diffuse urothelial thickening of the urinary bladder is most commonly due to cystitis, usually infectious, drug-induced, or radiation-related (Fig. 12); however, it can also result from chronic outlet obstruction in which case it may be associated with increased bladder wall trabeculation. When focal, CTU cannot reliably differentiate benign from malignant urothelial thickening necessitating cystoscopic and/or ureteroscopic evaluation with possible biopsy for definitive diagnosis. CTU and Radiation Exposure A primary concern regarding the widespread use of CTU has been its associated relatively high radiation dose (at least in comparison to EU). Estimates of the effective dose for CTU vary widely, with doses greater than 20-30 mSv not uncommon depending on the imaging protocol used.1 As with any imaging test that uses ionizing radiation, the risks of patient radiation exposure must be weighed against the potential
Figure 9 Prominent papilla simulating a filling defect. Seventy-fouryear-old man with a history of bladder cancer undergoing routine surveillance double-bolus CTU examination. Axial (A) and coronal (B) images demonstrate a filling defect (arrows) within a right upper pole calyx. This finding was stable over 3 years and represents a prominent renal papilla.
urinary bladder. Prominent renal papillae that indent and project into the calyces may also, on occasion, be mistaken for urothelial neoplasms (Fig. 9). Rarely, a ureteral kink (Fig. 10) or crossing vessel (Fig. 11) may mimic urothelial neoplasm, appearing as a filling defect on axial imaging due to oblique sectioning through the folded portion of the urinary tract wall. Fortunately, both of these anatomic variants are usually easily diagnosed with the aid of reformatted imaging. Crossing vessels can often be traced to the nearby abdominal aorta or inferior vena cava. Benign Urothelial Thickening Benign thickening of upper tract and urinary bladder urothelium can mimic “flat” neoplasms. Benign urothelial thickening may be either focal or diffuse. Benign focal urothelial thickening may be due to urolithiasis, inflammation/infection, or recent instrumentation. Benign diffuse urothelial thickening is thought to be most commonly inflammatory in
Figure 10 Ureteral kink. Sixty-one-year-old woman undergoing double-bolus CTU examination for asymptomatic hematuria. Axial image (A) demonstrates a linear filling defect (arrows) near the right ureteropelvic junction that on a coronal reformatted image (B) is easily diagnosed as a ureteral kink (arrows).
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Figure 11 Crossing vessels presenting as apparent filling defects. (A) Sixty-one-year-old woman with hematuria referred for CTU due to multiple apparent filling defects (arrows) within the left ureter seen at EU. Coronal-oblique maximum intensity projection (MIP) image (B) demonstrates similar findings to the EU image (arrows). Axial image (C) confirms that the left ureter (black arrowheads) apparent filling defects are due to extrinsic impression from an adjacent crossing vessel (white arrowheads).
benefits. CTU should be used only in appropriate clinical settings. We believe that comprehensive CTU examinations (particularly those involving 3 separate imaging phases) should be avoided in pediatric, young adult, and pregnant patients, if at all possible. As a result, the authors have attempted to restrict CTU use at their institution to patients who are believed to be at increased risk of having a urothelial neoplasm (such as elderly patients with a smoking history, patients with suspicious or positive urine cytology, and patients who have previously been treated for a urothelial neoplasm). In a review of CTU examinations performed at our institution over a 5-year period (2000-2005), there was no significant change in referral pattern or in rate of urothelial neoplasm detection despite a 150% increase in usage.42 This finding suggests that, at our institution, most patients referred for CTU are at similarly increased risk for urothelial neoplasm as patients referred for CTU when the study first became available. Whether this finding holds true for other patient populations and other institutions, however, is not known. When CTU is performed, there are multiple strategies that can and should be employed to minimize radiation dose. First, tube current (mA), which is directly proportional to
patient radiation dose, can be reduced or an automated exposure control system (automated tube current modulation) can be used. Second, fewer imaging phases can be obtained, either by eliminating a phase in its entirety if it is not required to answer the clinical question or by adopting a double- or triple-bolus technique, which combines imaging phases. At our institution, switching from a single-bolus 3-phase imaging protocol to a double-bolus 2-phase imaging protocol resulted in an estimated effective dose reduction of approximately 30%.10 In addition, many institutions, including ours, have adopted a variety of different CTU protocols for different indications. For example, we obtain unenhanced CTU images only for the first CTU examination in patients who will require multiple follow-up studies. If no renal calculi are detected and any present renal masses are characterized sufficiently, unenhanced scans will be omitted on subsequent CTU examinations. At some institutions where furosemide is administered, the unenhanced scans have been omitted from all examinations, because most calculi can be detected on excretory phase images. Newer imaging techniques and advances in technology, such as dual-energy digital iodine subtraction, may provide additional options for dose reduction in the future, including possible elimination of the noncontrast imaging phase.43,44
Computed Tomographic Urography Update: An Evolving Urinary Tract Imaging Modality Zachary W. Washburn, MD, Jonathan R. Dillman, MD, Richard H. Cohan, MD, Elaine M. Caoili, MD, MS, and James H. Ellis, MD Multi-detector computed tomography urography (CTU) is now well established as the imaging modality of choice for comprehensive evaluation of the kidneys and urinary tract, having largely replaced excretory urography. Over the past decade, CTU techniques have continued to evolve with the goal of improving urothelial surface visualization. Numerous benign and malignant conditions of the kidneys, ureters, and urinary bladder can be accurately depicted by CTU. This article provides a contemporary review of CTU imaging protocols, image postprocessing techniques, appearances of various urinary tract pathologic conditions, and pitfalls in image interpretation. Semin Ultrasound CT MRI 30:233-245 © 2009 Elsevier Inc. All rights reserved.
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ver the past decade, multidetector computed tomography urography (CTU) has become the imaging modality of choice for comprehensive evaluation of the kidneys and urinary tract. To distinguish CTU from other CT techniques (for example, protocols tailored to evaluate for urolithiasis or renal masses), a recently proposed definition stated that CTU should be optimized for evaluation of the urinary tract and must include excretory phase imaging.1 A combination of unenhanced CT imaging to evaluate for urolithiasis and to provide a baseline image to characterize masses, nephrographic phase imaging to evaluate for benign and malignant renal parenchymal processes, and excretory phase imaging to evaluate for abnormalities of the urothelium, CTU has largely replaced excretory urography (EU). Much recent effort has been aimed at optimizing excretory phase urinary tract distension and opacification with the hope that greater separation of the urothelial surfaces and outlining the entire urothelium with excreted contrast would provide a more detailed evaluation of urothelium, enhancing the sensitivity for lesion detection. In addition, recent effort has gone into reducing patient radiation exposure related to CTU, as this imaging technique has been associated with relatively high radiation doses when compared with EU.1-7 Several authors have advocated the use of tailored CTU protocols rather than a “onesize-fits-all” approach.1,2 For example, radiation exposure University of Michigan Health System, Department of Radiology, C.S. Mott Children’s Hospital, Ann Arbor, MI. Address reprint requests to Jonathan R. Dillman, MD, University of Michigan Health System, Department of Radiology, C.S. Mott Children’s Hospital, F3503, 1500 E. Medical Center Dr., Ann Arbor, MI 48109-5252. E-mail: [email protected]
0887-2171/09/$-see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1053/j.sult.2009.03.005
can be reduced by eliminating certain imaging phases based on the specific clinical question and patient risk factors. CTU is most commonly performed for the evaluation of hematuria, especially in patients at increased risk of urothelial malignancy. Other indications include evaluation of urinary tract obstruction (including hydronephrosis and hydroureter of uncertain etiology), assessment of urinary diversion integrity after cystectomy, assessment of urinary tract trauma (including iatrogenic), evaluation of complicated infections (including fungal infections and tuberculosis), and determination of anatomy before difficult percutaneous nephrolithotomy cases. It is clear from this list of indications that CTU is effective at detecting many benign and malignant renal and urinary tract conditions.
Techniques Contrast Material Administration Single-Bolus Technique The original CTU technique, still in use today, calls for 3 imaging phases and uses a single intravenous bolus injection of contrast material.3 An unenhanced phase is initially performed to evaluate patients for urinary calculi, to establish a baseline for assessment of any subsequently detected lesion enhancement, and to assist in the characterization of certain masses, such fat-containing angiomyolipomas, where noncontrast images may more clearly depict tissue attenuation characteristics. Following contrast material administration, 2 additional phases are obtained. Nephrographic phase imaging is performed approximately 100-120 seconds after the initiation of contrast material injection to evaluate the en233
Computed tomographic urography update 22. Claebots C, Puech P, Delomez J, et al: MDCT urography with and without use of diuretics. J Radiol 88:1697-1702, 2007 23. Roy C, Jeantroux J, Irani FG, et al: Accuracy of intermediate dose of furosemide injection to improve multidetector row CT urography. Eur J Radiol 66:253-261, 2008 24. Nolte-Ernsting CC, Wildberger JE, Borchers H, et al: Multi-slice CT urography after diuretic injection: Initial results. Rofo 173:176-180, 2001 25. Kemper J, Regier M, Stork A, et al: Improved visualization of the urinary tract in multidetector CT urography (MDCTU): Analysis of individual acquisition delay and opacification using furosemide and low-dose test images. J Comput Assist Tomogr 30:751-757, 2006 26. Meindl T, Coppenrath E, Kahlil R, et al: MDCT urography: Retrospective determination of optimal delay time after intravenous contrast administration. Eur Radiol 16:1667-1674, 2006 27. Meindl T, Coppenrath E, Degenhart C, et al: MDCT urography: Experience with a bi-phasic excretory phase examination protocol. Eur Radiol 17:2512-2518, 2007 28. Dillman JR, Caoili EM, Cohan RH, et al: Detection of upper tract urothelial neoplasms: Sensitivity of axial, coronal reformatted, and curved-planar reformatted image-types utilizing 16-row multi-detector CT urography. Abdom Imaging 33:707-716, 2008 29. Mitsumori A, Yasui K, Akaki S, et al: Evaluation of crossing vessels in patients with ureteropelvic junction obstruction by means of helical CT. RadioGraphics 20:1383-1393, 2000 30. Raman SS, Pojchamarnwiputh S, Muangsomboon K, et al: Surgically relevant normal and variant renal parenchymal and vascular anatomy in preoperative 16-MDCT evaluation of potential laparoscopic renal donors. AJR Am J Roentgenol 188:105-114, 2007 31. Sudakoff GS, Guralnick M, Langenstroer P, et al: CT urography of urinary diversions with enhanced CT digital radiography: Preliminary experience. AJR Am J Roentgenol 184:131-138, 2005 32. Lang EK, Macchia RJ, Thomas R, et al: Multiphasic helical CT diagnosis of early medullary and papillary necrosis. J Endourol 18:49-56, 2004
245 33. Jung DC, Kim SH, Jung SI, et al: Renal papillary necrosis: Review and comparison of findings at multi-detector row CT and intravenous urography. Radiographics 26:1827-1836, 2006 34. Harvin HJ: Ureteral fibroepithelial polyp on MDCT urography. AJR Am J Roentgenol 187:434-435, 2006 35. Hall MC, Womack S, Sagalowsky AI, et al: Prognostic factors, recurrence, and survival in transitional cell carcinoma of the upper urinary tract: A 30-year experience in 252 patients. Urology 52:594-601, 1998 36. Tsili AC, Efremidis SC, Kalef-Ezra J, et al: Multi-detector row CT urography on a 16-row CT scanner in the evaluation of urothelial tumors. Eur Radiol 17:1046-1054, 2007 37. Fritz GA, Schoellnast H, Deutschmann HA, et al: Multiphasic multidetector-row CT (MDCT) in detection and staging of transitional cell carcinomas of the upper urinary tract. Eur Radiol 16:1244-1252, 2006 38. Turney BW, Willatt JM, Nixon D, et al: Computed tomography urography for diagnosing bladder cancer. BJU Int 98:345-348, 2006 39. Knox MK, Cowan NC, Rivers-Bowerman MD, et al: Evaluation of multidetector computed tomography urography and ultrasonography for diagnosing bladder cancer. Clin Radiol 63:1317-1325, 2008 40. Shadow CA, Silverman SG, O’Leary MP, et al: Bladder cancer detection with CT urography in an Academic Medical Center. Radiology 249: 195-202, 2008 41. Lui W, Mortelé KJ, Silverman SG: Incidental extraurinary findings at MDCT urography in patients with hematuria: Prevalence and impact on imaging costs. AJR Am J Roentgenol 185:1051-1056, 2005 42. Kielar AZ, Ellis JH, Cohan RH, et al: Computed tomography urography: Trends in positivity rates over time. J Comput Assist Tomogr 32:46-53, 2008 43. Takahashi N, Hartman RP, Vrtiska TJ, et al: Dual-energy CT iodinesubtraction virtual unenhanced technique to detect urinary stones in an iodine-filled collecting system: A phantom study. AJR Am J Roentgenol 190:1169-1173, 2008 44. Brown CL, Hartman RP, Dzyubak OP, et al: Dual-energy CT iodine overlay technique for characterization of renal masses as cyst or solid: A phantom feasibility study. Eur Radiol 2009 (in press)
O
ver the past decade, multidetector computed tomography urography (CTU) has become the imaging modality of choice for comprehensive evaluation of the kidneys and urinary tract. To distinguish CTU from other CT techniques (for example, protocols tailored to evaluate for urolithiasis or renal masses), a recently proposed definition stated that CTU should be optimized for evaluation of the urinary tract and must include excretory phase imaging.1 A combination of unenhanced CT imaging to evaluate for urolithiasis and to provide a baseline image to characterize masses, nephrographic phase imaging to evaluate for benign and malignant renal parenchymal processes, and excretory phase imaging to evaluate for abnormalities of the urothelium, CTU has largely replaced excretory urography (EU). Much recent effort has been aimed at optimizing excretory phase urinary tract distension and opacification with the hope that greater separation of the urothelial surfaces and outlining the entire urothelium with excreted contrast would provide a more detailed evaluation of urothelium, enhancing the sensitivity for lesion detection. In addition, recent effort has gone into reducing patient radiation exposure related to CTU, as this imaging technique has been associated with relatively high radiation doses when compared with EU.1-7 Several authors have advocated the use of tailored CTU protocols rather than a “onesize-fits-all” approach.1,2 For example, radiation exposure University of Michigan Health System, Department of Radiology, C.S. Mott Children’s Hospital, Ann Arbor, MI. Address reprint requests to Jonathan R. Dillman, MD, University of Michigan Health System, Department of Radiology, C.S. Mott Children’s Hospital, F3503, 1500 E. Medical Center Dr., Ann Arbor, MI 48109-5252. E-mail: [email protected]
0887-2171/09/$-see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1053/j.sult.2009.03.005
can be reduced by eliminating certain imaging phases based on the specific clinical question and patient risk factors. CTU is most commonly performed for the evaluation of hematuria, especially in patients at increased risk of urothelial malignancy. Other indications include evaluation of urinary tract obstruction (including hydronephrosis and hydroureter of uncertain etiology), assessment of urinary diversion integrity after cystectomy, assessment of urinary tract trauma (including iatrogenic), evaluation of complicated infections (including fungal infections and tuberculosis), and determination of anatomy before difficult percutaneous nephrolithotomy cases. It is clear from this list of indications that CTU is effective at detecting many benign and malignant renal and urinary tract conditions.
Techniques Contrast Material Administration Single-Bolus Technique The original CTU technique, still in use today, calls for 3 imaging phases and uses a single intravenous bolus injection of contrast material.3 An unenhanced phase is initially performed to evaluate patients for urinary calculi, to establish a baseline for assessment of any subsequently detected lesion enhancement, and to assist in the characterization of certain masses, such fat-containing angiomyolipomas, where noncontrast images may more clearly depict tissue attenuation characteristics. Following contrast material administration, 2 additional phases are obtained. Nephrographic phase imaging is performed approximately 100-120 seconds after the initiation of contrast material injection to evaluate the en233
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234 hancement characteristics of renal parenchymal lesions, while excretory phase imaging is performed after a much greater time delay (to allow for ample urinary tract opacification) to assess the urothelium. Advantages of this technique include its ease of contrast material administration and the complete evaluation of the kidneys and urinary tract it affords. Its primary disadvantage is the relatively high patient radiation exposure due to 3 separate imaging phases. Double-Bolus Technique As its name implies, the double-bolus CTU technique relies on 2 separate administrations of intravenous contrast material separated by a specific amount of time.8,9 This technique allows for the acquisition of a combined nephrographic-excretory imaging phase following unenhanced imaging. The double-bolus approach has several advantages over the single-bolus technique, including decreased patient radiation dose (because only 1 series of enhanced images is obtained), fewer images to archive, and fewer images to review. A theoretic disadvantage of this technique is that it may produce less urinary tract distension when compared with the singlebolus technique (because only the first of the 2 administered boluses opacifies the urinary tract and contributes to contrast-induced diuresis at the time of image acquisition). Dillman et al10 showed that the only significant differences in distension between the 2 techniques occurred at the level of the renal collecting systems (and not the ureters). Another concern regarding this technique is the theoretic risk that renal collecting system urothelial lesions might be obscured on combined nephrographic-excretory phase images due to adjacent renal enhancement.2 Despite these concerns, Chow et al11 reported high sensitivity and specificity (100% and 99%, respectively) for detection of urothelial tumors in the renal collecting systems and renal pelvises using this method. Triple-Bolus Technique Kekelidze et al12 described a novel CTU technique that combines arterial, nephrogenic, and excretory phase information into a single imaging acquisition. This technique requires the intravenous administration of 3 separate boluses of contrast material, each separated by a specific amount of time, before a single acquired contrast-enhanced series of images. Triplebolus CTU allows for the anatomic evaluation of renal arterial vasculature, including the number and course of the renal arteries, without the additional patient radiation dose of a separate arterial imaging phase acquisition. The advantages and disadvantages of this technique are generally similar to those of the double-bolus technique; however, for any given contrast dose, the total volume of contrast material opacifying the renal parenchyma and excreted into the renal collecting systems will be even smaller (because the total dose must now be split into 3 boluses), with the theoretic risk of compromising assessment of renal masses and urothelial lesions. This technique has not gained widespread acceptance, likely due to a combination of protocol complexity and the fact that in most patients referred for CTU (with hematuria and/or suspected urothelial lesions, for example), there is little interest in assessing them for renal artery pathology. This tech-
nique may be useful, however, in the evaluation of potential living renal donors.
Ancillary Maneuvers Patient Positioning The use of prone positioning during excretory phase imaging has shown mixed results when evaluated for its effects on urinary tract opacification. Most investigators perform CTU with the patient in the supine position. Prone positioning for CTU was initially thought to favorably affect urinary tract opacification,3 but it has since been shown to be of little benefit, especially when compared with other ancillary techniques.13,14 However, prone positioning may occasionally be useful in some patients. For example, it can be employed to distinguish dependent bladder calculi from impacted ureterovesical junction calculi at unenhanced imaging.2 Several maneuvers have been recommended to facilitate the mixing of excreted contrast and urine in the bladder or any dilated portions of the renal collecting systems and ureters to obtain more homogeneous urinary tract opacification and avoid fluid-fluid (contrast-urine) levels. Such homogeneous opacification may improve sensitivity in the detection of urothelial lesions, especially in the bladder. Uniform opacification has been obtained in a variety of ways, including asking patients to void before the beginning of the examination (without moving or turning the patient), turning (or “log rolling”) the patient on the CT scanner, and even having the patient get off the CT scanner table and walk around the CT room before excretory phase image acquisition.15 While “log-rolling” maneuvers may have no effect on opacification of normal ureters;15 this technique has been used to improve opacification of dilated collecting systems.16 Oral Hydration Positive enteric contrast material is not used with CTU, because it can interfere with the identification of the contrast opacified mid and distal ureters as well as compromise the quality of subsequently created 3-dimensional (3D) reconstructed images. Oral administration of up to 1000 mL of water 20-60 minutes before excretory phase imaging may be useful, as it acts both as a negative contrast agent within bowel and as a means of patient hydration, thereby potentially improving distension of ureteral segments due to resulting increased diuresis.17 Urinary tract opacification may also be improved after oral hydration. Such opacification has been found to be greatest if water is ingested 60 minutes rather than 15-20 minutes before excretory phase imaging.17,18 When furosemide is also used, oral hydration with water can lessen any risk of dehydration. Abdominal Compression External abdominal compression, which has been used for years during EU, has also been used during CTU. It has been presumed that abdominal compression would improve renal collecting system and proximal ureteral distension and opacification when it is applied, and that distension and opacification of the mid and distal ureters would be improved upon compression release. Initial studies using this
Computed tomographic urography update technique reported improved opacification of the ureters.3,8 However, Caoili et al19 found no significant improvement in urinary tract distension when using abdominal compression; furthermore, urinary tract opacification was improved more using intravenous hydration and delayed acquisition timing than by abdominal compression. From a practical standpoint, compression bands are cumbersome to apply, somewhat uncomfortable for the patient, and demanding of technologists’ time. Abdominal compression is also contraindicated in certain patients, including those with recent abdominal or pelvic surgery, abdominal aortic aneurysm, and acute urinary tract obstruction. For these reasons, the use of external abdominal compression bands during CTU has largely been abandoned in favor of other ancillary maneuvers. Intravenous Hydration Intravenous hydration before CTU image acquisition using normal (0.9%) saline has been used to improve image quality with mixed results. Expansion of the intravascular volume with this technique was expected to enhance diuresis and augment urinary tract opacification and distension. Using a 250 mL intravenous bolus, Caoili et al19 reported a small, but significant, improvement of urinary tract opacification and distension. McTavish et al,13 using a similar technique, also reported improved urinary tract opacification. Conversely, Sudakoff et al20 found no additional benefit in urinary tract opacification with an intravenous saline bolus, while Silverman et al21 found that there was no additional benefit to a saline infusion when intravenous furosemide was administered. Most researchers have found that an intravenous saline bolus is well-tolerated by nearly all patients, although particular care should be taken when hydrating volume-sensitive patients (for example, individuals with congestive heart failure). At the present time, despite its only mild efficacy, this technique is still used widely. Furosemide Low-dose intravenous furosemide (usually at doses of between 5 and 20 mg) has been used to augment urinary tract distension and opacification. Using a 10 mg dose, Sanyal et al14 found that the distal ureters could be opacified in 93% of cases, which represented improved opacification when compared with imaging performed without a diuretic. Other authors have reported similar findings using 20 mg furosemide.22,23 Multiple authors have reported that superior urinary tract opacification could be obtained with furosemide compared to saline infusion alone.14,21,24 Another potential advantage of a diuretic is the diminished concentration of the excreted contrast material in the renal collecting systems and ureters that it produces. Such diminished concentration may allow for detection of high-attenuation calculi in the urinary tract even on excretory phase images and also might reduce possible streak artifacts that could obscure visualization of small urothelial lesions.24 While low-dose diuretics are generally safe and well-tolerated by most patients, some precautions are needed if furosemide is to be used. This medication is contraindicated in patients with sulfa drug allergies. In addition, it should be
235 used with caution in patients with hypokalemia, hypotension, dehydration, acute renal failure, acute ureteral obstruction, anuria, as well as in those receiving certain medications, such as ototoxic agents.
Excretory Phase Imaging Delay Time Traditionally, CTU has been performed using a fixed excretory phase delay time. The ideal delay time should allow for complete opacification of the renal collecting systems, ureters, and bladder. Reliable opacification of the mid and distal ureteral segments has proven to be one of the greatest challenges in CTU. While McNicholas et al3 used a fixed excretory delay time of 10 minutes (600 s), a wide range of delay times (ranging from 3 to 15 min) have been proposed. This variation may be, at least in part, due to other differences in CTU protocols and ancillary maneuvers employed. For example, the optimal excretory delay time is shortened when using furosemide compared with imaging performed without furosemide.25 In a protocol using intravenous saline hydration, Caoili et al19 found that an imaging delay of 450 seconds improved distension of the upper urinary tract compared with a delay of 300 seconds. Meindl et al,26 also using a protocol with intravenous saline hydration, reported that a more prolonged delay of 10-16 minutes (median, 11 min) improved opacification of the distal ureter without having an adverse impact on opacification of the proximal ureter and renal collecting system. Using a similar protocol, the same investigators analyzed the value of performing both early (median 11 min) and late (median, 16 min) excretory phase imaging and found no significant difference in opacification between these 2 delay times.27 In a protocol using low-dose furosemide, Kemper et al25 individualized excretory phase delay time using periodic “low-dose test scans” through the distal ureters. They found that the median time delay required for maximal urinary tract opacification was 420 seconds (with a standard deviation of 121 s) in patients with normal renal function. Only 7.8% of distal ureters were not opacified using this method. In the same study, the difficult challenge of timing excretory phase imaging in the setting of urinary tract obstruction was also addressed. In patients with unilateral ureteral obstruction, the range of time to opacification of the affected ureter was 10-33 minutes.25
Image Postprocessing and Viewing Current generation multidetector helical CT scanners allow for the acquisition of volumetric data. Such data can be used to generate both submillimeter axial images and thicker reconstructed axial sections with increased signal-to-noise ratio. At our institution, using a 64-channel multidetector CT scanner, excretory-phase images are acquired using 32 ⫻ 1.25 mm collimation. The 1.25-mm source axial images are then used to reconstruct a separate imaging series with 2.5-mm images with 1.25 mm of section overlap. The thicker images are typically reviewed, with the source data used only to create the 2-dimensional reformatted and 3D recon-
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Z.W. Washburn et al Curved-planar reformatted (CPR) images depict a large portion of the urinary tract on a single image (as opposed to MPR images that display smaller portions of the urinary tract on a single image due to structures moving into or out of the plane of reformation).8,21 Potential drawbacks to this form of image reformation include the increased time needed to create the images on a 3D workstation and the potential for
Figure 1 Urothelial polyp. Eighty-nine-year-old man with a history of bladder cancer undergoing routine follow-up double-bolus CTU examination. Axial CTU image (A) viewed with a wide window/level setting demonstrates a small filling defect (arrow) in the right renal collecting system that proved to be a urothelial polyp after endoscopic biopsy. The same level (B) viewed with a narrow window/ level setting shows how a small filling defect can be missed (arrow) if the urothelium is not evaluated using appropriate window/level settings.
structed images. The urothelium should be evaluated using wide window/level settings (often similar to those used to view the skeleton) to avoid missing subtle urothelial abnormalities that may be obscured by adjacent hyperattenuating contrast material (Fig. 1). Volumetric source data allow for the creation of isotropic 2-dimensional reformatted images in any plane as well as a variety of forms of 3D image reconstruction. Coronal and sagittal multi-planar reformatted (MPR) images (including oblique reformations) are particularly useful for characterizing urinary tract pathology. This is due to the craniocaudal orientation of the urinary tract and the superior ability of multiplanar reformations to depict structures that traverse the z-axis.
Figure 2 Horseshoe kidney. Forty-one-year-old man undergoing double-bolus CTU examination for evaluation of microscopic hematuria. Volume-rendered image viewed anteriorly (A) displays midline lower pole renal fusion. An enhancing parenchymal isthmus (arrow) was located below the inferior mesenteric artery (with the latter seen on the axial images). Axial CTU image (B) reveals normal caliber ureters coursing anterior to lower moiety renal parenchyma (arrows).
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Figure 3 Duplicated urinary tract with ureterocele. Fifty-nine-yearold woman with chronic right flank pain undergoing double-bolus CTU for evaluation of right-sided pelvicaliectasis demonstrated at ultrasound. Volume-rendered image viewed anteriorly (A) demonstrates a duplicated right renal collecting system and ureter. There is mild dilatation of both the upper and the lower moiety renal collecting systems and ureters. The upper moiety ureter inserted just inferior to the insertion of the lower moiety ureter (not shown). Coronal reformatted (B) and axial (C) images demonstrate the right upper moiety ureter terminating in a ureterocele (white arrows). Orthotopic insertion of the unduplicated left ureter is also visible (black arrow).
distortion of anatomy and pathology due to the reformatting process itself. Dillman et al28 recently demonstrated similar sensitivities for axial, coronal reformatted, and CPR images in the retrospective detection of upper tract urothelial neoplasms, although the sensitivity for detecting these neoplasms increased significantly when axial, MPR, and CPR images were used in combination. Use of maximum-intensity projection and average-intensity projection images was first described for use with CTU by McNicholas et al.3 These 3D reconstruction techniques are used to display the entire volumetric data set on a single image or multiple images (depending on slab thickness). Such images are most commonly displayed in the coronal plane and appear somewhat similar to traditional EU images. While maximum-intensity projection and average-intensity projection images may lack sufficient detail to diagnose certain urothelial abnormalities, such as small filling defects and areas of subtle wall thickening, they do provide a useful format to display and evaluate urinary tract anatomy.
The volumetric data set can also be used to generate 3D volume-rendered (VR) images of the kidneys and urinary tract.4 VR images provide a 3D representation of the kidneys and opacified portions of the upper urinary tract and urinary bladder (or postsurgical urinary reservoir) and can be rotated and viewed in any plane. The diagnostic accuracy in detecting small urothelial lesions is very limited for this type of image reconstruction as only the luminal surface is displayed. For example, in 1 review of CTU examinations performed in patients with known urothelial neoplasms, only 25% could be detected using VR images.6 Furthermore, renal parenchymal lesions can only be detected reliably on VR images when they are large enough to distort the renal contour or when they protrude from the renal surface. When using double-bolus CTU technique, it may be difficult to discriminate the opacified urinary tract from briskly enhancing adjacent renal parenchyma.2 The VR reconstruction technique can be convenient for displaying complicated renal and urinary tract anatomy in a single image (Figs. 2 and 3); however, the diagnostic utility of these VR reconstructions is often limited.
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Imaging of Developmental Anatomic Variants Renal and urinary tract developmental anatomic variants, as well as their potential complications, can be evaluated with CTU. Renal ectopia (including crossed renal ectopia), horseshoe kidney, and renal agenesis are all straightforwardly diagnosed by CTU (Fig. 2).4,8 Urinary tract duplication also is usually easily detected by CTU and should be a diagnostic consideration in the setting of isolated superior pole renal collecting system dilatation.4,8 When duplication is present, CTU can define the exact site of the typically ectopic upper moiety ureter insertion as well as evaluate for the presence of a ureterocele. On CTU, ureteroceles may appear as a round or oval filling defect within the urinary bladder at or near the site of ureter insertion. The ureterocele may contain either central low or high attenuation depending on whether it contains excreted contrast material at the time that it is imaged (Fig. 3). Ectopic ureteral insertions and ureteroceles are rarely detected in the setting of a nonduplicated upper urinary tract. CTU (particularly when using the triple-bolus technique) can be useful in the evaluation of ureteropelvic junction obstruction and assessment of potential living renal donors. CTU can determine which ureteropelvic junction obstructions are due to an extrinsic cause, such as an aberrant renal artery or crossing vein.29 Similarly, CTU may play an important role in the preoperative evaluation of potential living renal donors. In addition to assessing patients for unknown renal and urinary tract pathology, CTU may influence surgical decision-making by providing important anatomic knowledge about the renal vasculature (including the number and course of the renal arteries and veins) and the urinary tract. The anatomic information provided on CTU can be used to determine which kidney will be chosen for donor nephrectomy.30
Imaging of the Postsurgical Urinary Tract CTU can be a useful problem-solving tool in the evaluation of numerous postoperative complications following urinary tract surgery, especially in of the setting of urinary tract diversion with complicated neobladder reconstruction. Postoperative complications that may be diagnosed and characterized by CTU include urinary tract obstruction, ureteral kinks or strictures, anastomotic leaks, and postoperative fluid collections.31
Figure 4 Renal tubular ectasia (medullary sponge kidney). Seventyseven-year-old man with history of bladder cancer undergoing routine follow-up double-bolus CTU examination. Axial (A) and coronal subvolume maximum intensity projection (MIP) (B) images demonstrate numerous abnormal collections of contrast material within the renal medullae that have a “brush-like” appearance (arrows).
Imaging of Benign Acquired Renal and Urinary Tract Conditions Examples of acquired benign renal and urinary tract conditions that can be evaluated with CTU include renal tubular ectasia (medullary sponge kidney), renal papillary necrosis, and pyeloureteritis/cystitis cystica. Renal tubular ectasia is due to abnormal medullary collecting tubule dilatation. The appearance of renal tubular ectasia on CTU and EU are similar (Fig. 4),8 with the abnormal linear collections of contrast material identified within the renal medulla classically described as having a “brush-like” appearance. CTU findings that suggest renal papillary necrosis include renal papillary hypoenhancement (suggesting impaired perfu-
sion) and abnormal contrast-filled cavities in the renal medulla located just peripheral to the calyces. Occasionally, a sloughed renal papilla may present as a urinary tract filling defect (Fig. 5A) and be difficult to differentiate from other abnormalities, including urothelial neoplasm. Additional findings that may be observed in the setting of longstanding renal papillary necrosis include club-shaped minor calyces, rim-like medullary calcifications, and cortical atrophy (Fig. 5B).32,33 In pyeloureteritis cystica and cystitis cystica, numerous tiny suburothelial cystic structures are formed in response to chronic inflammation (most commonly secondary to recurrent urolithi-
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Imaging of Urinary Tract Malignancy Urothelial neoplasms, predominantly of the transitional cell type, are the most common malignancies to affect the upper urinary tract and urinary bladder. Like most carcinomas, these neoplasms are initially noninvasive with prognosis significantly worsening following invasion of tumor into the underlying muscularis propria.35 Therefore, diagnosis of these neoplasms at an early stage is of the utmost importance. Urothelial neoplasms are most commonly solitary, but a large number of individuals develop either synchronous or metachronous lesions (Fig. 7). As a result, complete urinary tract evaluation is necessary at the time of diagnosis as well as when follow-up imaging is performed. Because patients with
Figure 5 Renal papillary necrosis. Thirty-one-year-old man undergoing double-bolus CTU for new-onset gross hematuria and history of heavy nonsteroidal anti-inflammatory drug use. Coronal reformatted image (A) demonstrates a filling defect (arrows) within the left upper pole renal collecting system, which proved to be a sloughed renal papilla at endoscopy. Coronal reformatted image (B) from a 54-year-old woman with a history of bladder cancer demonstrates a collection of contrast material extending from renal collecting system into adjacent medulla (black arrow) and a blunted calyx (white arrow) with thinning of the overlying cortex, changes consistent with papillary necrosis.
asis or infection). These entities can be detected on CTU and usually present as multiple, tiny mural-based filling defects. Benign urinary tract masses can also be detected with CTU. Ureteral fibroepithelial polyps are rare benign urothelial proliferative lesions that usually produce long slender urinary tract filling defects. The point of attachment of these structures to the ureteral wall can often be visualized.34 These lesions often have a strongly suggestive imaging appearance. Urothelial polyps (Fig. 1) and papillomas (Fig. 6) can also be detected and produce urinary tract filling defects, which cannot be differentiated from urothelial malignancy by their CTU appearance.
Figure 6 Urothelial papilloma vs. low-grade urothelial neoplasm. Fifty-nine-year-old woman undergoing double-bolus CTU for right flank pain. Axial image (A) demonstrates a filling defect (arrows) in the right upper pole renal collecting system, pathologically proven to be a urothelial papilloma. Axial image (B) from a 69-year-old man undergoing double-bolus CTU for the evaluation of gross hematuria demonstrates a similar-appearing right upper pole renal collecting system filling defect (arrows), pathologically proven to be a malignant low-grade noninvasive urothelial neoplasm.
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Figure 7 Upper urinary tract urothelial neoplasm. Curved-planar reformatted CTU image (A) demonstrates multiple polypoid filling defects (arrows) within the left renal pelvis and ureter in an 89year-old woman with known multifocal urothelial neoplasm and hematuria. A simple cyst (labeled C) is present within the upper pole of the left kidney. Coronal reformatted image (B) from a 63year-old woman with hematuria demonstrates a small polypoid filling defect (arrowhead) within the distal right ureter that proved to be a malignant low-grade noninvasive urothelial neoplasm. Axial image (C) from a 47-year-old man with hematuria demonstrates circumferential thickening (arrows) of the right ureter that proved to be high-grade noninvasive urothelial neoplasm with flat architecture.
urothelial malignancies are felt to have “at-risk” urothelium, they will usually have extensive follow-up after diagnosis, even in cases where noninvasive tumors are removed in their entirety by transurethral resection. Reliable detection of urothelial neoplasms by CTU has been demonstrated in multiple small series.6,11,28,36,37 At CTU, many upper urinary tract neoplasms present as single or multiple irregular filling defects (Figs. 6 and 7), similar to their classically described appearance at EU.28 Large urothelial neoplasms may also present as a focal mass. However, other appearances have been described. In a study by Caoili et al, just over 50% of upper tract neoplasms produced focal
circumferential wall thickening (Fig. 7).6 In some of these cases, the thickening did not produce urinary tract narrowing or irregularity, indicating that these neoplasms likely could not be detected with EU. At CTU, urinary bladder urothelial neoplasms present similarly to upper tract malignancies, appearing as focal wall thickening (Fig. 8A), intraluminal filling defects (Fig. 8B), or large masses (Fig. 8C). CTU has recently played an increasing role in the detection of bladder urothelial neoplasms, a role traditionally held by cystoscopy. Turney et al38 found CTU to have high sensitivity (93%) and specificity (99%) in detecting bladder cancer when compared to cystoscopy in evaluating
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Figure 8 Bladder urothelial neoplasm. Axial CTU image (A) from a 59-year-old man with hematuria reveals focal left posterior urinary bladder wall urothelial thickening (arrows), proven to be highgrade invasive urothelial neoplasm. Axial image (B) from a 63-yearold man with hematuria shows 2 polypoid filling defects (arrows) within the urinary bladder, proven to be high-grade invasive urothelial neoplasms. Sagittal reformatted image (C) from a 75year-old man with hematuria reveals a large, lobulated, partially calcified mass (arrows) extending through the anterior urinary bladder (arrowheads), proven to be high-grade invasive urothelial neoplasm.
patients greater than 40 years of age with hematuria. Similarly, Knox et al39 found CTU to be highly sensitive (90%) and specific (97%) in a study using cystoscopy with pathologic confirmation as the gold standard. Another study by Shadow et al40 determined that CTU has a high negativepredictive value (95%) in the evaluation of bladder cancers and suggested that further evaluation with cystoscopy may not be needed in certain low-risk patients with negative imaging. We believe that CTU cannot be considered a sufficient substitute for cystoscopy because small and flat tumors remain extremely difficult or even impossible to detect by imaging; however, CTU may be the first study to identify a bladder neoplasm. Furthermore, in a few instances, CTU has detected bladder neoplasms that were missed during cystoscopy.38 Both CTU and cystoscopy have difficulty in the evaluation of bladders in patients who have previously been treated for noninvasive bladder cancers. This is because the bladder wall may become inflamed and scarred following transurethral resection, intravesical immunotherapy, or chemotherapy. In these instances, the 2 studies may play a complementary role in evaluating the bladder.
Incidental Findings Owing to the ability to evaluate other intra-abdominal organs, CTU frequently detects findings outside of the urinary tract. Lui et al41 found incidental extraurinary tract findings to be present in 75.3% of CTU cases performed for the evaluation of hematuria, although only 12.5% were considered highly clinically significant (ie, requiring additional imaging workup or clinical intervention). The most common findings in this category were indeterminate lung nodules and enlarged abdominal lymph nodes. Despite this high prevalence of incidental findings, the extra costs created by additional imaging evaluation of these unexpected unrelated findings was less than $50 per CTU examination performed.
Pitfalls in CTU Interpretation Nonneoplastic and Apparent Filling Defects A variety of benign conditions can cause single or multiple urinary tract intraluminal filling defects that may mimic neoplasm. Blood clots, sloughed renal papillae (Fig. 5), mycetomata (fungus balls), and the exceedingly rare low-attenuation urinary calculus may present as solitary or multiple filling defects within the renal collecting systems, ureters, or
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Z.W. Washburn et al etiology. Benign diffuse urothelial thickening of the urinary bladder is most commonly due to cystitis, usually infectious, drug-induced, or radiation-related (Fig. 12); however, it can also result from chronic outlet obstruction in which case it may be associated with increased bladder wall trabeculation. When focal, CTU cannot reliably differentiate benign from malignant urothelial thickening necessitating cystoscopic and/or ureteroscopic evaluation with possible biopsy for definitive diagnosis. CTU and Radiation Exposure A primary concern regarding the widespread use of CTU has been its associated relatively high radiation dose (at least in comparison to EU). Estimates of the effective dose for CTU vary widely, with doses greater than 20-30 mSv not uncommon depending on the imaging protocol used.1 As with any imaging test that uses ionizing radiation, the risks of patient radiation exposure must be weighed against the potential
Figure 9 Prominent papilla simulating a filling defect. Seventy-fouryear-old man with a history of bladder cancer undergoing routine surveillance double-bolus CTU examination. Axial (A) and coronal (B) images demonstrate a filling defect (arrows) within a right upper pole calyx. This finding was stable over 3 years and represents a prominent renal papilla.
urinary bladder. Prominent renal papillae that indent and project into the calyces may also, on occasion, be mistaken for urothelial neoplasms (Fig. 9). Rarely, a ureteral kink (Fig. 10) or crossing vessel (Fig. 11) may mimic urothelial neoplasm, appearing as a filling defect on axial imaging due to oblique sectioning through the folded portion of the urinary tract wall. Fortunately, both of these anatomic variants are usually easily diagnosed with the aid of reformatted imaging. Crossing vessels can often be traced to the nearby abdominal aorta or inferior vena cava. Benign Urothelial Thickening Benign thickening of upper tract and urinary bladder urothelium can mimic “flat” neoplasms. Benign urothelial thickening may be either focal or diffuse. Benign focal urothelial thickening may be due to urolithiasis, inflammation/infection, or recent instrumentation. Benign diffuse urothelial thickening is thought to be most commonly inflammatory in
Figure 10 Ureteral kink. Sixty-one-year-old woman undergoing double-bolus CTU examination for asymptomatic hematuria. Axial image (A) demonstrates a linear filling defect (arrows) near the right ureteropelvic junction that on a coronal reformatted image (B) is easily diagnosed as a ureteral kink (arrows).
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Figure 11 Crossing vessels presenting as apparent filling defects. (A) Sixty-one-year-old woman with hematuria referred for CTU due to multiple apparent filling defects (arrows) within the left ureter seen at EU. Coronal-oblique maximum intensity projection (MIP) image (B) demonstrates similar findings to the EU image (arrows). Axial image (C) confirms that the left ureter (black arrowheads) apparent filling defects are due to extrinsic impression from an adjacent crossing vessel (white arrowheads).
benefits. CTU should be used only in appropriate clinical settings. We believe that comprehensive CTU examinations (particularly those involving 3 separate imaging phases) should be avoided in pediatric, young adult, and pregnant patients, if at all possible. As a result, the authors have attempted to restrict CTU use at their institution to patients who are believed to be at increased risk of having a urothelial neoplasm (such as elderly patients with a smoking history, patients with suspicious or positive urine cytology, and patients who have previously been treated for a urothelial neoplasm). In a review of CTU examinations performed at our institution over a 5-year period (2000-2005), there was no significant change in referral pattern or in rate of urothelial neoplasm detection despite a 150% increase in usage.42 This finding suggests that, at our institution, most patients referred for CTU are at similarly increased risk for urothelial neoplasm as patients referred for CTU when the study first became available. Whether this finding holds true for other patient populations and other institutions, however, is not known. When CTU is performed, there are multiple strategies that can and should be employed to minimize radiation dose. First, tube current (mA), which is directly proportional to
patient radiation dose, can be reduced or an automated exposure control system (automated tube current modulation) can be used. Second, fewer imaging phases can be obtained, either by eliminating a phase in its entirety if it is not required to answer the clinical question or by adopting a double- or triple-bolus technique, which combines imaging phases. At our institution, switching from a single-bolus 3-phase imaging protocol to a double-bolus 2-phase imaging protocol resulted in an estimated effective dose reduction of approximately 30%.10 In addition, many institutions, including ours, have adopted a variety of different CTU protocols for different indications. For example, we obtain unenhanced CTU images only for the first CTU examination in patients who will require multiple follow-up studies. If no renal calculi are detected and any present renal masses are characterized sufficiently, unenhanced scans will be omitted on subsequent CTU examinations. At some institutions where furosemide is administered, the unenhanced scans have been omitted from all examinations, because most calculi can be detected on excretory phase images. Newer imaging techniques and advances in technology, such as dual-energy digital iodine subtraction, may provide additional options for dose reduction in the future, including possible elimination of the noncontrast imaging phase.43,44
Computed Tomographic Urography Update: An Evolving Urinary Tract Imaging Modality Zachary W. Washburn, MD, Jonathan R. Dillman, MD, Richard H. Cohan, MD, Elaine M. Caoili, MD, MS, and James H. Ellis, MD Multi-detector computed tomography urography (CTU) is now well established as the imaging modality of choice for comprehensive evaluation of the kidneys and urinary tract, having largely replaced excretory urography. Over the past decade, CTU techniques have continued to evolve with the goal of improving urothelial surface visualization. Numerous benign and malignant conditions of the kidneys, ureters, and urinary bladder can be accurately depicted by CTU. This article provides a contemporary review of CTU imaging protocols, image postprocessing techniques, appearances of various urinary tract pathologic conditions, and pitfalls in image interpretation. Semin Ultrasound CT MRI 30:233-245 © 2009 Elsevier Inc. All rights reserved.
O
ver the past decade, multidetector computed tomography urography (CTU) has become the imaging modality of choice for comprehensive evaluation of the kidneys and urinary tract. To distinguish CTU from other CT techniques (for example, protocols tailored to evaluate for urolithiasis or renal masses), a recently proposed definition stated that CTU should be optimized for evaluation of the urinary tract and must include excretory phase imaging.1 A combination of unenhanced CT imaging to evaluate for urolithiasis and to provide a baseline image to characterize masses, nephrographic phase imaging to evaluate for benign and malignant renal parenchymal processes, and excretory phase imaging to evaluate for abnormalities of the urothelium, CTU has largely replaced excretory urography (EU). Much recent effort has been aimed at optimizing excretory phase urinary tract distension and opacification with the hope that greater separation of the urothelial surfaces and outlining the entire urothelium with excreted contrast would provide a more detailed evaluation of urothelium, enhancing the sensitivity for lesion detection. In addition, recent effort has gone into reducing patient radiation exposure related to CTU, as this imaging technique has been associated with relatively high radiation doses when compared with EU.1-7 Several authors have advocated the use of tailored CTU protocols rather than a “onesize-fits-all” approach.1,2 For example, radiation exposure University of Michigan Health System, Department of Radiology, C.S. Mott Children’s Hospital, Ann Arbor, MI. Address reprint requests to Jonathan R. Dillman, MD, University of Michigan Health System, Department of Radiology, C.S. Mott Children’s Hospital, F3503, 1500 E. Medical Center Dr., Ann Arbor, MI 48109-5252. E-mail: [email protected]
0887-2171/09/$-see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1053/j.sult.2009.03.005
can be reduced by eliminating certain imaging phases based on the specific clinical question and patient risk factors. CTU is most commonly performed for the evaluation of hematuria, especially in patients at increased risk of urothelial malignancy. Other indications include evaluation of urinary tract obstruction (including hydronephrosis and hydroureter of uncertain etiology), assessment of urinary diversion integrity after cystectomy, assessment of urinary tract trauma (including iatrogenic), evaluation of complicated infections (including fungal infections and tuberculosis), and determination of anatomy before difficult percutaneous nephrolithotomy cases. It is clear from this list of indications that CTU is effective at detecting many benign and malignant renal and urinary tract conditions.
Techniques Contrast Material Administration Single-Bolus Technique The original CTU technique, still in use today, calls for 3 imaging phases and uses a single intravenous bolus injection of contrast material.3 An unenhanced phase is initially performed to evaluate patients for urinary calculi, to establish a baseline for assessment of any subsequently detected lesion enhancement, and to assist in the characterization of certain masses, such fat-containing angiomyolipomas, where noncontrast images may more clearly depict tissue attenuation characteristics. Following contrast material administration, 2 additional phases are obtained. Nephrographic phase imaging is performed approximately 100-120 seconds after the initiation of contrast material injection to evaluate the en233
Computed tomographic urography update 22. Claebots C, Puech P, Delomez J, et al: MDCT urography with and without use of diuretics. J Radiol 88:1697-1702, 2007 23. Roy C, Jeantroux J, Irani FG, et al: Accuracy of intermediate dose of furosemide injection to improve multidetector row CT urography. Eur J Radiol 66:253-261, 2008 24. Nolte-Ernsting CC, Wildberger JE, Borchers H, et al: Multi-slice CT urography after diuretic injection: Initial results. Rofo 173:176-180, 2001 25. Kemper J, Regier M, Stork A, et al: Improved visualization of the urinary tract in multidetector CT urography (MDCTU): Analysis of individual acquisition delay and opacification using furosemide and low-dose test images. J Comput Assist Tomogr 30:751-757, 2006 26. Meindl T, Coppenrath E, Kahlil R, et al: MDCT urography: Retrospective determination of optimal delay time after intravenous contrast administration. Eur Radiol 16:1667-1674, 2006 27. Meindl T, Coppenrath E, Degenhart C, et al: MDCT urography: Experience with a bi-phasic excretory phase examination protocol. Eur Radiol 17:2512-2518, 2007 28. Dillman JR, Caoili EM, Cohan RH, et al: Detection of upper tract urothelial neoplasms: Sensitivity of axial, coronal reformatted, and curved-planar reformatted image-types utilizing 16-row multi-detector CT urography. Abdom Imaging 33:707-716, 2008 29. Mitsumori A, Yasui K, Akaki S, et al: Evaluation of crossing vessels in patients with ureteropelvic junction obstruction by means of helical CT. RadioGraphics 20:1383-1393, 2000 30. Raman SS, Pojchamarnwiputh S, Muangsomboon K, et al: Surgically relevant normal and variant renal parenchymal and vascular anatomy in preoperative 16-MDCT evaluation of potential laparoscopic renal donors. AJR Am J Roentgenol 188:105-114, 2007 31. Sudakoff GS, Guralnick M, Langenstroer P, et al: CT urography of urinary diversions with enhanced CT digital radiography: Preliminary experience. AJR Am J Roentgenol 184:131-138, 2005 32. Lang EK, Macchia RJ, Thomas R, et al: Multiphasic helical CT diagnosis of early medullary and papillary necrosis. J Endourol 18:49-56, 2004
245 33. Jung DC, Kim SH, Jung SI, et al: Renal papillary necrosis: Review and comparison of findings at multi-detector row CT and intravenous urography. Radiographics 26:1827-1836, 2006 34. Harvin HJ: Ureteral fibroepithelial polyp on MDCT urography. AJR Am J Roentgenol 187:434-435, 2006 35. Hall MC, Womack S, Sagalowsky AI, et al: Prognostic factors, recurrence, and survival in transitional cell carcinoma of the upper urinary tract: A 30-year experience in 252 patients. Urology 52:594-601, 1998 36. Tsili AC, Efremidis SC, Kalef-Ezra J, et al: Multi-detector row CT urography on a 16-row CT scanner in the evaluation of urothelial tumors. Eur Radiol 17:1046-1054, 2007 37. Fritz GA, Schoellnast H, Deutschmann HA, et al: Multiphasic multidetector-row CT (MDCT) in detection and staging of transitional cell carcinomas of the upper urinary tract. Eur Radiol 16:1244-1252, 2006 38. Turney BW, Willatt JM, Nixon D, et al: Computed tomography urography for diagnosing bladder cancer. BJU Int 98:345-348, 2006 39. Knox MK, Cowan NC, Rivers-Bowerman MD, et al: Evaluation of multidetector computed tomography urography and ultrasonography for diagnosing bladder cancer. Clin Radiol 63:1317-1325, 2008 40. Shadow CA, Silverman SG, O’Leary MP, et al: Bladder cancer detection with CT urography in an Academic Medical Center. Radiology 249: 195-202, 2008 41. Lui W, Mortelé KJ, Silverman SG: Incidental extraurinary findings at MDCT urography in patients with hematuria: Prevalence and impact on imaging costs. AJR Am J Roentgenol 185:1051-1056, 2005 42. Kielar AZ, Ellis JH, Cohan RH, et al: Computed tomography urography: Trends in positivity rates over time. J Comput Assist Tomogr 32:46-53, 2008 43. Takahashi N, Hartman RP, Vrtiska TJ, et al: Dual-energy CT iodinesubtraction virtual unenhanced technique to detect urinary stones in an iodine-filled collecting system: A phantom study. AJR Am J Roentgenol 190:1169-1173, 2008 44. Brown CL, Hartman RP, Dzyubak OP, et al: Dual-energy CT iodine overlay technique for characterization of renal masses as cyst or solid: A phantom feasibility study. Eur Radiol 2009 (in press)