Evaluacion Del Urotelio Con UroTAC

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Evaluating the Urothelium With

CT Urography: Are We There Yet?Anne M. Silas, MD, FRCPC

Computed tomography urography (CTU) is a compre-hensive cross-sectional CT examination of the upperand lower urinary tract, before and after the intravenousadministration of contrast material, including excretoryphase imaging.1 The development of multidetector row CT(MDCT) has enabled the rapid acquisition of high-resolutionisotropic image data and the generation of high quality 3D

image reformations, which are paving the way for multide-tector CTU (MDCTU) to become the singular imaging eval-uation of the kidneys, renal collecting systems, ureters, andbladder.2 The increased radiation dose that is generated bythis examination warrants judicious use of this technique incertain patient populations and clinical scenarios.

Evaluation of the Urinary Tract

Individual unenhanced and multiphasic contrast-enhancedCT examinations have become well established for the detec-tion of calculi and renal parenchymal abnormalities.3,4 Beforethe advent of MDCT, however, CT was not considered areliable modality for the detection and staging of urothelialneoplasms.5,6 Even with the development of 4- and 8-sliceCT scanners, the lack of isotropic data resulted in missedurothelial lesions.7

Faster data acquisition, improved z-axis resolution, andshorter rotation gantry intervals inherent to 16- and 64-MDCT have resulted in improved spatial resolution and thecreation of excellent multiplanar reconstruction (MPR) and3D images, which resemble the traditional IV pyelogram.2

With this advanced technology, several studies have nowestablished the diagnostic usefulness of MDCTU for the eval-uation of the urinary tract8-10 (Fig. 1).

Indications

Hematuria is the most common indication for CTU. 11,12 A2005 survey of members of the Society of Urological Radiol-

ogy revealed that 94% believe CTU is indicated in the evalu-ation of painless hematuria (Fig. 2). Additional indicationsinclude microscopic painless hematuria, suspected transi-tional cell cancer, transitional cell cancer follow-up, and sus-pected congenital anomalies.11

The increased radiation dose that is inherent to CTU war-rants limiting the application of this study in patients aged

40 years. However, appropriateness of CTU is highly ratedby the American College of Radiology for the evaluation ofhematuria, excluding those with generalized renal parenchy-mal disease or young women with hemorrhagic cystitis.13

Additional indications for CTU include unexplained hy-dronephrosis, smoking, macroscopic compared to micro-scopic hematuria, exposure to aniline dyes, urinary tracttrauma (both iatrogenic and noniatrogenic), and 3D plan-ning for difficult cases of percutaneous nephrolithotomy andsurgical reconstruction14,15 (Figs. 3 and 4).

Technique

MDCTU encompasses the use of imaging through the abdo-men and pelvis without intravenous contrast, and multiple

Department of Radiology, Interventional Radiology and Abdominal Imag-

ing, Dartmouth-Hitchcock Medical Center, Lebanon, NH.

Address reprint requests to Anne M. Silas, MD, FRCPC, Department of

Radiology, Dartmouth-Hitchcock Medical Center, One Medical Center

Dr, Lebanon, NH 03756. E-mail: [email protected]

Figure 1 Single thick slab excretory phase maximum intensity pro-

jection (MIP) image from a normal MDCTU.

244 0037-198X/09/$-see front matter 2009 Elsevier Inc. All rights reserved.doi:10.1053/j.ro.2009.06.001
mailto:[email protected]:[email protected]


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phases of imaging through the abdomen and pelvis after theadministration of intravenous contrast. These multiple se-quences are timed to optimize visualization of renal paren-

chymal and urinary tract structures.Noncontrast imaging through the abdomen and pelvis is

used for the detection of urinary tract calculi and calcifica-tions. Arterial phase imaging, typically 20-25 seconds aftercontrast injection, was used to evaluate vascular anomaliesand renal arterial anatomy in earlier CTU protocols, althoughits use in recent protocols has waned as renal masses are bestdemonstrated in the nephrographic phase.2 The nephro-graphic phase is imaged approximately 100 seconds aftercontrast administration. Finally, the urothelium is best im-aged in the excretory phase, typically a delay of several min-utes after IV contrast administration, which is subject to peri-

stalsis. Image and diagnostic quality of excretory phaseevaluation is, therefore, dependent on both distention and

opacification of the collecting system, ureters, and bladder1

(Fig. 5). Although originally, these 4 imaging phases wereused as part of the CTU examination, typically only 2-3

phases are used in current examination protocols to limitpatient radiation exposure.

To reduce the number of scans of the abdomen and pelvisand, therefore, reduce the overall radiation dose of the study,as well as the number of images generated, the nephro-graphic and excretory phases may be combined. This splitbolus technique is characterized by an initial administrationof the contrast and after delay, the administration of the re-mainder of the bolus before imaging the abdomen and pelvis.Imaging then takes advantage of excretion of the initial con-trast bolus as well as nephrographic enhancement of the renalparenchyma.16 It remains somewhat controversial whether

the split bolus technique yields similar sensitivity and speci-ficity to separated nephrographic and excretory phases.1,17

Figure 2 Transitional cell carcinoma (TCC) presenting as Gross hematuria and obstruction in an 81-year-old man. Axial

unenhanced (A), coronal nephrographic (B), and axial excretory phase (C) images show hyperdense nonenhancing throm-bus(white arrows), distending and obstructing theright renalcollecting system.Note theincidental nonobstructing calculus.

Excretory axial (D) and coronal (E) phase images from a repeat study performed one month following placement of aninternal ureteral stent show persistent delay of contrast excretion from the obstructed right collecting system as compared

withthe left.Heterogeneity within the partially opacified right collecting system and medial central and lower poleurothelialsoft tissue thickening (black arrows) is now shown. This was confirmed at biopsy to be TCC.

Evaluating the urothelium with CT urography 245


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Distention of the renal collecting systems and ureters remainsthe greatest limitation of this examination, and multiple tech-niques have been described to try optimizing this.

The application of abdominal compression during CTUhas not been shown to make any significant difference inopacification of the renal calices and pelves, nor of the upper

Figure 3 Bilateral collecting system rupture in a 56-year-old man

presenting with 2 days of hematuria following blunt trauma. Axialunenhanced (A) and nephrographic (B) phase images show bilateral

perinephricfluid, delayed left nephrogram and unenhancing hyper-dense thrombus distending and obstructing the left collecting sys-

tem (white arrows). Axial excretory phase images (C, D) show ret-

roperitoneal extravasation of opacified urine from bilateralcollecting system rupture (black arrows).

Figure 4 A 67-year-old woman with hematuriain the setting of dual largecalculi-containingbladderdiverticula and chronic bladderinfection. Foley

catheterin bladder andpigtailcatheter withinsupravesicalcollection. CTUordered for planning of surgical reconstruction and identification of fistu-

lae. Axial excretory (A) image in wide window setting shows thedistal leftureter (whitearrowhead)passing intoa calculus-containing bladderdiver-

ticulum(whitestar) andfistula fromdiverticulumtobladder(whitearrow).Note multiple filling defects consistent with calculi and debris within the

thickenedbladder. 3DMPR(B,C)demonstrate thepositionof thedistalleftureter (white arrowhead) and diverticular fistula to the bladder (white

arrow). (Colorversion of figure is available online.)

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and mid ureters when comparing CTU and IV urography(IVU).18 The distention of the distal ureters remains problem-atic. Although McNicholas et al18 found that scanning thepatient in the prone position may improve visualization ofthe distal ureters, this may not be feasible in practice when

attempting to image proximal portions of the upper tracts atthe same sitting. McTavish et al,19 however, showed im-proved opacification of distal ureters after IV saline infusion,with the patient in the supine position.

Caoili et al20 compared the use of abdominal compression,the administration of IV saline bolus, and extended excretoryphase delay periods. These investigators found that disten-tion of the intrarenal collecting systems and proximal andmid ureters was greater when compression was applied,when a saline bolus was given, and when the excretory delaywas increased from 300 seconds to 450 seconds after contrastinjection. Furthermore, Curic et al21 demonstrated that im-

aging in the excretory phase 1 hour after the ingestion of1000 mL of water, as opposed to imaging at 20 minutes,

resulted in improved distention of the urinary tract. Theypostulated that prolonged hydration-to-imaging intervalpromotes diuresis compounded with the obstructing effect ofthe distended urinary bladder, resulting in improved visual-ization of the urinary tract, including the distal ureters.

Additional maneuvers, such as log rolling, have not shownany difference in ureteral opacification.22

Finally, the intravenous administration of furosemide hasbeen described as an effective method of collecting systemdistention. The administration of 10 mg IV furosemide 3-5minutes before contrast injection has been shown to improvepelvicaliceal detail and ureteric opacification at CTU, result-ing in less heterogeneity in the collecting system than theadministration of IV saline alone.23-25

Axial images acquired with thin beam collimation haveresulted in improved three-dimensional (3D) datasets thathave enabled high quality postprocessing 3D reformations.

This volumetric information may ultimately replace conven-tional urography as long as viewing and evaluation is per-

Figure 5 Multiple imaging phases of CTU. Unenhanced (A), arterial (B), nephrographic (C), and excretory (D) phase axialimages from a normal CT urogram. Note that renal contrast enhancement is cortical in the arterial phase (B) although

distributes into the medulla at nephrographic phase (C). Excretory phase (D) shows contrast opacifying the collectingsystems.



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Figure 6 Multifocal TCC within proximal collecting system and ureter in a 79-year-old man presenting with macro-

scopichematuria; utility of wide windowsettingsand MPRimages. Axial soft tissueexcretoryphase imagesat twolevels(A, B) through the right kidney show multiple filling defects in the central collecting system and proximal ureter (white

arrows). Axial images at the same level as image B in thin section (C) and wide window settings (D) illustrate enhanced

detail of disease burden and mucosal abnormalities. Wide window coronal (E, F) and MIP (G) excretory phase imagesdemonstrate these multifocal lesions (white arrows).

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formed with thin-section images using wide windows (Fig.6). Reviewing thin axial section images with MPR scan mayalso aid in the detection of bladder tumors26 (Fig. 7). Addi-tional techniques, such as virtual CT endoscopy, have beendescribed for urothelial evaluation.27

DetectionCT has become well established as a diagnostic modality forthe detection of renal calculi and renal parenchymal abnor-malities.28,29 Combining these noncontrast and multiphasiccontrast-enhanced examinations with excretory phase imag-

Figure 7 Multifocal TCC in a 72-year-old woman presenting withgross hematuria. Excretory axial (A) and coronal (B) phase images

show subtle infiltrative left interpolar renal mass (open star) withcalyceal invasion (white arrow) and blunting as well as urothelial

thickening (white arrows) in the central renal pelvis. Note rigidstraightened appearance of the left ureterovesical junction (UVJ)

(white arrows). Note incidental upper pole renal cyst (open trian-gle). Coronal MIP image in wide window settings (C) show calyceal

invasion (white arrow) and additional focus of disease within theproximal left ureter (thick white arrow).

Figure 8 Recurrent TCC presenting as solid renal mass with collect-

ing system invasion in an 80-year-old man status post cystectomyand creation of ileal conduit. Axial (A, B) and coronal (C) excretory

phase images show a hypodense infiltrative interpolar right renalmass (white star) with collecting system invasion characterized by

central collecting system filling defects and calyceal distortion(white arrows).



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ing using MDCT has recently been shown to be an effectiveimaging modality for the diagnosis of urothelial lesions.

As compared to IVU, CTU has better sensitivity (100% vs60.5%), specificity (97.4% vs 90.9%), and accuracy (98.3%vs 80.9%) in the evaluation of asymptomatic microhematu-ria.30 Supporting these findings, in a prospective study, Langetal9 found that CTU was 91% sensitive and 94% specific forthe detection of lesions causing microscopic hematuria.

Mueller-Lisse et al31 have reported 94% MDCTU sensitiv-ity for the evaluation of urothelial lesions in patients having ahistory of previous urothelial malignancy or painless macro-scopic hematuria. MDCT can detect wall thickening that may

not result in alteration of ureteral caliber and, therefore, mayremain undetectable at IVU. MDCTU sensitivity and speci-

Figure 9 Multifocal TCC presenting as macroscopic hematuria in an

82-year-old man. Coronal unenhanced images show multiple fillingdefects within the dilated right renal collecting system (thin black

arrows) and proximal ureter (solid black arrow) (A) and severecircumferential bladder wall thickening (thick black arrow) (B).

Figure 10 Bilateralrenal cellcarcinomapresenting as gross hematuria in

a 72-year-old woman. Unenhanced axial image shows bilateral solidrenal masses (white star) (A). Note dystrophic calcification within the

larger left renal mass. Nephrographic axial image (B) shows complexpartially necrotic bilateral renal masses with complete replacement of

the left renal parenchyma. Note the right retroperitoneal lymphade-nopathy (white diamonds). Axial (C) excretory phase wide window

image shows bilateral calyceal and right ureteric invasion (white ar-

rows). Coronal excretory phase image (D) shows frank tumoral inva-sion into the central left renal collecting system.

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ficity will likely increase as these examinations are performedon CT scanners with greater number of detectors, such as 16-and 64-MDCT scanners. As compared to conventional radi-ography, filling defects as small as 0.25 mm were identified inphantom models at 64-MDCT, whereas only 3 of these le-sions were missed when scanned in the 16-MDCT system.32

Estimated Radiation Dose

The greater the number of imaging phases used in MDCTU,the greater the overall radiation dose will be. Although over-

all radiation dose may play a lesser role in a patient popula-tion with a high suspicion of malignant disease, dose remainsa significant issue, particularly for populations of youngerpatients or those with benign disease.17

Dose reduction, in the form of lower mAs or kV settings onthe basis of patient weight, as well as the use of fewer scansmay yield sufficient diagnostic information, particularlywhen the scan is tailored to the patient age and clinical sce-nario.14,32,33 Kemper et al34 showed that adequate image soft-

tissue detail in pigs could be maintained with significantlylow mAs settings. Furthermore, lower kV settings can also

Figure 11 Multiple examples of polypoid intravesical masses in patients presenting with hematuria. Coronal and axialnephrographic images (A, B) through the pelvisin a 66-year-old woman show left bladder mass in the regionof the UVJ

(white arrow). Axial images (C, D) through the bladder of a 75-year-old man show multiple polypoid bladder lesions(white arrows). Axial and coronal (E, F) excretory phase images in a 61-year-old man show right UVJ lesion (white

arrow).



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reduce overall radiation dose without affecting contrast-to-noise ratio.35

Newer automated tube current modulation software auto-matically varies CT radiation dose on the basis of patientbody habitus. Constant image noise is preserved while main-taining image quality during the examination. Mean effectiveCTU dose has decreased since CTU was first used and has

now been reported to be as low as 9-15 mSv. 36,37 However,discretion toward the application of this relatively high doseexamination is warranted.

Imaging UrothelialLesions of the Upperand Lower Urinary Tract

Collecting System and UretersAt CTU, urothelial carcinoma may present as hypodense sol-itary or multiple soft-tissue masses that may enhance. These

masses may be infiltrative. Thickening of the wall of the col-lecting system or ureter has been described.38 Nonneoplas-tic- and inflammatory disorders may mimic neoplastic le-sions.39 Reviewing thin section axial images as well as curved-

Figure 12 TCC presenting as macroscopic hematuria in a 74-year-

old man. Axial (A, B) excretory images through the bladder showexophytic hypodense left UVJ mass (black arrows) encasing albeit

not obstructing the left distal ureter and UVJ. 3D MPR (C) confirmsposition of this mass (identified in blue) with respect to the ureter.

(Color version of figure is available online.)

Figure 13 Radiation cystitis in a 75-year-old man status post treat-ment for prostate cancer who presented with hematuria. Axial soft

tissue (A) and wide window (B) images through the bladder showthis to be severely irregular and thick walled (arrows).

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planar and MPR images in a wide window setting is requiredto maximize detection. Dillman et al40 found that reviewingmultiple types of images versus reviewing only a single serieswhen interpreting CTU yielded detection sensitivity forurothelial neoplasm to a maximum of 94% on 16-sliceMDCT scanners (Figs. 8-10).

BladderMDCTU for the detection of bladder malignancy remainscontroversial. Cystoscopy has long been considered the goldstandard for the detection and diagnosis of bladder lesions.12

These lesions can present as flat tumors that have gone un-detected at CTU performed with earlier generation scanners.Sadow et al10 found that the overall sensitivity of CTU for thedetection of bladder cancer was less than that of cystoscopy(95.3% vs 78.5%). They also showed that the negative pre-dictive value of CTU was less than that of cystoscopy (95.3%vs 98.9%), although the sensitivity of CTU was greater in thesetting of gross hematuria. Turney et al,41 however, com-pared MDCTU with flexible cystoscopy for the detection ofbladder lesions in patients aged 40 years presenting withmacroscopic hematuria on an 8-slice scanner, and found thatCT sensitivity and specificity were 93% and 99%, respec-tively, whereas positive and negative predictive values were98% and 97%, respectively (Figs. 11-13).

Conclusion

MDCTU has become a highly sensitive and specific compre-hensive imaging modality for the urothelial system and may

be a suitable first-line screening examination for patientsaged 40 years with macroscopic hematuria. Distention ofthe collecting systems and ureters is a persistent limitation ofthe study, and multiple maneuvers may be used to maximizeopacification of these organs. Given the increased radiationdose that accompanies this examination as compared withconventional imaging modalities, judicious use of multiplephases and tailoring of the study to the clinical conditionbeing evaluated is recommended.

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