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Genitourinary Imaging |
1 From the Depts of Radiology (J.H.S., I.R.F., J.F.P., R.H.C., J.M., M.K.) and Urology (S.J.K., J.E.M.), University of Michigan Hospital, UH B2B311D/0030, 1500 E Medical Center Dr, Ann Arbor, MI 48109-0030. From the 1999 RSNA scientific assembly. Received March 7, 2000; revision requested April 11; revision received May 30; accepted June 28. Address correspondence to J.H.S. (e-mail: songjul@umich.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Twenty-six patients suspected or known to have bladder neoplasms underwent CT virtual and conventional cystoscopy. The bladder was insufflated with carbon dioxide through a Foley catheter. Helical CT of the bladder was then performed. The data were downloaded to a workstation for interactive intraluminal navigation. Two radiologists blinded to the results of conventional cystoscopy independently reviewed the transverse and virtual images, with consensus readings for cases with discrepant results.
RESULTS: Thirty-six (90%) of 40 bladder lesions proved at conventional cystoscopy were detected with a combination of transverse and virtual images. Four (10%) of 40 bladder lesions, all smaller than 5 mm, were undetected. Transverse and virtual images were complementary, since six polypoid lesions smaller than 5 mm depicted on the virtual images were not seen on the transverse images. In contrast, areas of wall thickening were more readily appreciated on transverse images. CT with patients in both supine and prone positions was necessary, since seven (19%) and five (14%) of 36 lesions were seen only on supine and prone images, respectively.
CONCLUSION: CT virtual cystoscopy is a promising technique for use in bladder tumor detection of lesions larger than 5 mm. Optimal evaluation requires adequate bladder distention with the patient in both supine and prone positions and interpretation of both transverse and virtual images.
Index terms: Bladder neoplasms, 83.30 • Bladder neoplasms, CT, 83.12111, 83.12115 • Computed tomography (CT), helical, 83.12115 • Computers, diagnostic aid
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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While excretory urography is generally performed to examine the upper urinary tract for synchronous tumors, which occur in 2.3% of patients with transitional cell carcinoma of the urinary bladder (2), it can also be used to detect other abnormalities, such as stones or masses, that could account for the patient’s hematuria. Computed tomography (CT) and magnetic resonance (MR) imaging are used mainly to demonstrate extravesical extension of the tumor and distant metastasis. Routine surveillance consists of periodic excretory urography, cystoscopy, and bladder washing with cytologic analysis. CT and MR imaging are follow-up studies reserved for patients with invasive disease. Cross-sectional imaging has had little or no role, to date, in the initial evaluation of patients in whom a bladder lesion is suspected.
Recently, three-dimensional computer-rendering techniques with rapid image acquisition have led to the development of virtual-reality imaging. With commercially available software, virtual-reality imaging allows interactive intraluminal navigation through any hollow viscus, simulating conventional endoscopy. This technique of virtual endoscopy has been applied to many organs, including the colon, bronchus, stomach, and bladder (3–13).
In this study, we investigated the utility of virtual cystoscopy in the detection of bladder lesions.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Twenty-eight CT virtual cystoscopic examinations were performed between February and December 1998. Two patients underwent examination twice. The examinations were performed in 26 native bladders and two orthotopic neobladders. With the exception of the patients with a neobladder, all patients underwent conventional cystoscopy with either a flexible or rigid cystoscope. The time between conventional and CT cystoscopy ranged from 0 to 143 days; 23 (88%) of 26 patients underwent both examinations within 2 weeks. The two patients with a neobladder were followed up clinically up to 14 and 18 months.
The technique for cystoscopy began with the placement of a 12-F Foley catheter into the bladder to drain residual urine. The bladder was then insufflated with 300–500 mL of carbon dioxide through the Foley catheter, according to patient tolerance.
After a scout view was obtained with the patient in the supine position to locate the bladder and confirm its adequate distention, single–breath-hold helical CT was performed with one of two scanners (HiSpeed Advantage or HiSpeed CTi; GE Medical Systems, Milwaukee, Wis), with 3-mm collimation, pitch of 1:1, 120 kVp, and 220 mA.
Images were reconstructed at 1-mm intervals by using the minimal field of view measured from the inner aspect of the middle of the pelvis. The patient was then turned to the prone position, and helical CT of the bladder was repeated with use of the same parameters after a repeat scout view was obtained. Additional bladder distention with approximately 100 mL of CO2 was necessary in about half of the patients, since repositioning led to leakage of some of the insufflated gas from the bladder. Virtual cystoscopy time, including catheter placement, was approximately 30 minutes.
The data were downloaded to an independent workstation (Advantage Windows 3.1; GE Medical Systems) equipped with software (Navigator; GE Medical Systems) for interactive intraluminal navigation with a surface-rendering algorithm. The threshold was optimized at -500 HU. Although an initial learning curve was observed with navigation and interpretation of virtual cystoscopic findings, the mean interpretation time for each examination was approximately 15 minutes.
Two radiologists (J.H.S., J.F.P.) blinded to the findings of conventional cystoscopy independently interpreted the images prospectively, and any discrepant readings were resolved by consensus.
The 
statistic was used to determine the interreader reliability, and the following guideline was used to interpret the estimated value for strength of agreement: A value of less than 0.20 was poor; 0.21–0.40, fair; 0.41–0.60, moderate; 0.61–0.80, good; and 0.81–1.00, very good (14).
The number, size, location, and morphologic features of the lesions were evaluated on transverse and virtual images obtained with the patients in both the supine and prone positions. Each lesion was characterized as a focal polypoid lesion, a sessile mass, or wall thickening. A discrete lesion was considered polypoid if it was taller than it was wide, while a sessile mass was defined as a lesion that was wider at the base. A lesion was characterized as wall thickening when there was elevation of the bladder wall without a discrete mass.
The quality of each image was also evaluated in terms of the residual urine, which may obscure the bladder mucosa, and the degree of distention. Complications due to CT cystoscopy were recorded.
The results of CT virtual cystoscopy were compared with the findings of conventional cystoscopy, which is considered the standard. The lesions that were not prospectively identified at CT cystoscopy were retrospectively evaluated for visibility on transverse and virtual images. The pathology report in each patient was also reviewed for further correlation.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Conventional cystoscopy depicted 40 lesions in 22 of 26 examinations. At pathologic evaluation, the lesions in 12 examinations were carcinomas, and the lesions in the remaining 10 examinations were a chronic inflammation, granulomatous reaction, scar, or dysplasia. The histologic diagnosis was not available for every lesion because some of the small lesions were fulgurated at conventional cystoscopy.
At CT cystoscopy, the readers independently detected 35 (88%) and 32 (80%) of 40 proved lesions. The two readers initially agreed on all but five lesions on four virtual cystoscopic images. All five lesions were confirmed to be present by consensus.
The statistic for the data was 0.73, which represented good interreader agreement. By consensus, at CT virtual cystoscopy, 36 (90%) of these 40 lesions were identified as 15 focal polypoid lesions, five sessile masses, and 16 instances of wall thickening.
These masses ranged from 0.3 to 7.0 cm in diameter (mean, 1.5 cm). Of the 15 polypoid lesions, nine were larger than 5 mm, and six were 5 mm or smaller. Two of the polypoid lesions were calcified; one measured 8 mm and the other, 20 mm. A mass (pathologically proved transitional cell carcinoma) growing into a bladder diverticulum was detected at virtual cystoscopy (Fig 1).
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There were six patients with true-negative findings in our study, four with native bladders and two with neobladders. At CT cystoscopy, the neobladders appeared different from the native bladders, with the neobladders having visible ileal folds.
There were no false-positive findings in our series. The presence of every lesion seen at virtual cystoscopy was confirmed at conventional cystoscopy.
Transverse and virtual images were complementary in lesion detection and characterization. All six polypoid lesions of less than 5 mm were identified only on the virtual images, even in retrospect (Fig 2). Two of these small lesions accounted for some of the discrepant results between the two readers.
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There was one complication at virtual cystoscopy related to catheter removal. An 80-year-old man developed an inability to void due to hemorrhage and intravesical clot formation following virtual cystoscopy and required bladder irrigation for clot retention. The patient was hemodynamically stable and did not require a blood transfusion or hospital admission.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The recent introduction of virtual endoscopy adds to the imaging armamentarium for use in bladder evaluation. The volumetric data obtained with helical CT or MR imaging are computer-rendered to generate three-dimensional images, and with commercially available software, intraluminal navigation through any hollow viscus is possible. Of the different three-dimensional rendering techniques available, perspective volume rendering provides the most information because the entire data set is incorporated (16,17); however, it requires a more powerful computer than do other three-dimensional techniques, such as shaded-surface display or maximum intensity projection. Virtual endoscopy has been most widely applied to imaging of the colon (virtual colonoscopy), and many investigators (4–6) report its feasibility in the depiction of colorectal polyps. Since the original article by Vining et al (9), there have been several studies (10–13) of the utility of virtual endoscopy of the bladder.
In this study, we demonstrated that virtual cystoscopy is a feasible technique for use in the detection of bladder lesions larger than 5 mm. For lesions 5 mm and smaller, our detection rate was 60% (six of 10). In a study of 27 patients, Narumi et al (10) detected 77% of lesions smaller than 10 mm. Separately, Fenlon et al (11) identified all lesions smaller than 10 mm in their study of 13 patients. The 100% detection rate reported by Fenlon et al may in part be attributable to their use of the perspective volume-rendering technique, a technique that is more sensitive for lesion detection than the surface-rendering algorithm used in our study. Since neither of these groups of investigators reported how many of their lesions were smaller than 5 mm, it is impossible to directly compare our results with those of the two studies.
Our study findings contribute to the growing literature about virtual cystoscopy in that we also assessed two factors that could optimize lesion detection. First, regarding the type of view, we showed that transverse and virtual views are complementary in lesion detection and characterization; therefore, sets of both of these images should be used for accurate lesion detection. Second, comparing patient position, we found that 33% (12 of 36) of the lesions were seen on only supine or prone views. Imaging in both positions is necessary for visualization of the entire mucosal surface without obscuration caused by residual urine. Similar results concerning the value of imaging the patient in both positions at virtual colonoscopy have been reported (6).
As a minimally invasive procedure, virtual cystoscopy provides many advantages. It allows accurate localization of a lesion due to its wide field of view and depiction of extravesical anatomic landmarks. The size of a tumor is measured objectively, and virtual cystoscopy can be used to monitor treatment response in a patient with a nonresectable tumor. Patients with a severe ureteral stricture or marked prostatic hypertrophy, who may be poor candidates for conventional cystoscopy, can safely undergo CT cystoscopy, since a small ureteral catheter can be used to instill air into the bladder (13). Use of the transverse images during CT cystoscopy also allows for comprehensive pelvic imaging to assess extravesical metastases.
There are several important limitations of virtual cystoscopy. A major limitation is that it is unable to depict flat lesions (carcinoma in situ), which appear as subtle mucosal color changes at conventional cystoscopy. The current resolution of helical CT does not allow reliable and consistent visualization of small (<5 mm) lesions. In addition, mucosal thickening secondary to fibrosis cannot be distinguished from a neoplasm. Of course, with conventional cystoscopy, one faces a similar problem because biopsy is often required to determine whether a bladder lesion is inflammatory, fibrotic, or neoplastic. Another disadvantage of virtual cystoscopy is that it lacks the ability to provide tissue for histologic evaluation, an ability that is possible with conventional cystoscopy and biopsy.
One potential limitation of our study is that many patients could not undergo both conventional and virtual cystoscopy on the same day due to scheduling considerations. However, 23 of 26 patients underwent both examinations within 2 weeks of each other, and any detectable change of a lesion during that short period was expected to be negligible.
Our study is also potentially limited by a skewed patient population, since many of the patients were referred for evaluation in a tertiary center. All patients had either a previous or recent diagnosis of bladder neoplasm. Many patients had scarring from previous tumor resection, which made interpretation more difficult. However, the readers were blinded to patient history and cystoscopic findings at the time of the image interpretation.
In conclusion, CT virtual cystoscopy is a promising technique for use in the detection of bladder lesions larger than 5 mm. Adequate bladder distention and analysis of both transverse and virtual images obtained with the patient in both supine and prone positions are required for optimal evaluation.
Although the clinical utility of CT virtual cystoscopy has not yet been established, it may have several potential roles. CT cystoscopy can serve as a complementary examination performed between conventional cystoscopic examinations in a patient with bladder cancer who is undergoing treatment. It can be used as a diagnostic examination in a patient suspected or known to have bladder cancer who is not a candidate for conventional cystoscopy. In the future, it may be possible or even advantageous to incorporate it into the imaging algorithm for evaluation of hematuria. To determine the clinical value of CT virtual cystoscopy, however, a larger prospective study in the general patient population is necessary.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Author contributions: Guarantors of integrity of entire study, J.H.S., I.R.F., J.F.P.; study concepts, I.R.F., J.F.P.; study design, J.H.S., I.R.F., J.F.P., R.H.C., J.M., M.K., J.E.M.; definition of intellectual content, J.H.S., I.R.F., J.F.P.; literature research, J.H.S., I.R.F.; clinical studies, J.H.S., I.R.F., J.F.P., J.M.; data acquisition, I.R.F., J.M., R.H.C., S.J.K.; data analysis, J.H.S., J.F.P., I.R.F.; statistical analysis, J.H.S., J.F.P.; manuscript preparation, J.H.S.; manuscript editing, J.H.S., I.R.F., J.F.P., R.H.C., S.J.K., M.K.; manuscript review and final version approval, all authors.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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