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Original Research |
1 Department of Clinical Radiology, University Hospital of Ioannina, Leoforos S.
Niarchou, 45500, Pl. Pargis, 2, 45332, Ioannina, Greece.
2 Department of Urology, University Hospital of Ioannina, Ioannina,
Greece.
3 Department of Hygiene and Public Health, University Hospital of Ioannina,
Ioannina, Greece.
Received October 5, 2006;
accepted after revision September 19, 2007.
Address correspondence to A. C. Tsili
(a_tsili{at}yahoo.gr).
Abstract
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SUBJECTS AND METHODS. Fifty patients who presented with hematuria and a recent diagnosis or a history of bladder carcinoma underwent CT cystoscopy. All patients were examined in the supine and prone positions after bladder distention with room air. A detector configuration of 16 x 0.75 mm and a pitch of 1.2 was used. Virtual images were obtained with volume-rendered algorithms. Transverse tomographic slices, multiplanar reformatted images, and virtual images were prospectively evaluated separately and in combination. Conventional cystoscopy was considered the standard of reference for assessing the efficacy of MDCT cystoscopy in the detection of urinary bladder tumors.
RESULTS. Fifty-five (96%) of 57 urinary bladder lesions recognized at conventional cystoscopy were detected with MDCT cystoscopy. The size of the lesions ranged from 0.3 to 9.7 cm in diameter, including 18 lesions with a diameter of 0.5 cm or less. Transverse, multiplanar reformatted, and virtual images proved complementary for lesion detection.
CONCLUSION. MDCT cystoscopy is an accurate technique for the detection of uri-nary bladder neoplasms in patients at high risk, yielding satisfactory results in the identification of lesions smaller than 0.5 cm.
Keywords: bladder neoplasms • cystoscopy • MDCT
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Conventional cystoscopy plays a key role in the diagnosis and follow-up of bladder cancer. Virtual endoscopy is a minimally invasive technique that has promising results in the evaluation of the entire urinary tract [6–16]. CT virtual cystoscopy has been proposed as an alternative imaging technique with potential advantages in the detection of urinary bladder neoplasms and has good patient acceptance [6–11, 17–19]. One of the limitations of this technique is difficulty depicting small lesions.
The introduction of MDCT scanners was a major technologic advance because, among other things, it substantially improved z-axis (longitudinal) resolution by reducing section collimation and facilitating detection of very small lesions [20, 21]. The near isotropic pixels achieved with a 16-MDCT scanner enable acquisition of multiplanar reformatted (MPR) images with resolution very close to that of axial images and 3D renderings of outstanding quality. Use of a 64-MDCT scanner can improve image quality by further improving spatial resolution [22, 23]. The purpose of this study was to determine the feasibility and efficacy of 16-MDCT cystoscopy in the detection of urinary bladder neoplasms in a selected population of patients at high risk.
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Conventional cystoscopy with a flexible cystoscope was performed on all patients, and the suspicious lesions were biopsied. In 35 cases, CT cystoscopy was performed before conventional cystoscopy, and in 15 cases, after the cystoscopic procedure. The time interval between CT cystoscopy and conventional cystoscopy was less than 7 days. All CT examinations were performed with a 16-MDCT scanner (Mx8000 IDT, Philips Medical Systems). Preparation included placement of a 14-French Foley catheter into the urinary bladder for drainage of residual urine. The bladder was then distended with 300–500 mL of room air through the Foley catheter according to patient tolerance. Bladder distention was assessed on an anteroposterior planning scan projection radiograph obtained before CT data acquisition.
The patients were examined in both the supine and the prone positions. The Foley catheter was left in place throughout the examination to reinflate the bladder as needed. Scanning of the urinary bladder was performed with a minimal field of view according to the following parameters: 120 kV; detector collimation, 16 x 0.75 mm; section thickness, 1 mm; rotation time, 0.5 second; pitch, 1.2. The mean tube current–time product per rotation for each scan was calculated at 156 mAs because the tube current was modulated across the patient's body. Images were reconstructed at 1-mm intervals. Scanning of the region of the urinary bladder lasted 4 seconds on average, and the time for the whole procedure was approximately 5 minutes.
The axial tomographic slices were transferred to a workstation (MxView, Philips Medical Systems). MPR images 2 mm thick at 2-mm intervals were obtained in the transverse, coronal, and sagittal planes (Extended Brilliance v.1.0.1.1. software, Philips Medical Systems). The time to generate these images was less than 1 minute. Virtual cystoscopic images were obtained with the volume-rendering technique and the same software as for the MPR images. The average time for the creation of these images and navigation of the urinary bladder was approximately 2 minutes.
The axial, MPR, and virtual images were prospectively interpreted, both separately and in combination, by two radiologists with 4 years and 1 year of experience in virtual CT cystoscopy. These readers worked in consensus and were blinded to the results of conventional cystoscopy. The number, size, location, and morphologic features of the lesions were studied. Tumor size was classified into lesions with a diameter of 0.5 cm or less and those larger than 0.5 cm. The lesions were characterized as polypoid, sessile, and areas of wall thickening. A lesion was characterized as an area of wall thickening when there was no associated discrete mass. A lesion was considered polypoid if it protruded into the bladder lumen and was attached to the bladder wall by a narrow stack. A lesion was described as sessile if it was connected to the bladder wall by a broad base. The total time spent on study interpretation was approximately 7 minutes. Urinary bladder distention, presence of residual urine, and complications occurring during the procedure were recorded.
Detailed forms regarding number, estimated size, and location of bladder tumors found at conventional cystoscopy were completed by the urologists. The findings at MDCT cystoscopy were compared with those of conventional cystoscopy, which was considered the standard of reference. Both sets of findings were correlated with histologic diagnoses. The McNemar test was used to compare the diagnostic results based on axial, MPR, and virtual images with the findings at conventional cystoscopy. The free-in-air CT dose index was measured along the axis of rotation with a pencil-shaped ion chamber (type 10 x 5 10.3 CT, Radcal). The effective dose was calculated (ImPACT CT Patient Dosimetry Calculator, version 0.99 x 20/01/2006).
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The histologic diagnosis of transitional cell carcinoma was made in 30 cases, of transitional cell carcinoma with squamous or glandular differentiation in four cases, and of small cell carcinoma of the urinary bladder in one case (Fig. 2A, 2B). In one patient, CT cystoscopy showed a large mass on the wall of the urinary bladder in association with irregularity of the perivesical fat (Fig. 3A, 3B). This finding was thought to represent perivesical extension, but the abnormalities proved inflammatory at pathologic examination. In one patient, microscopic infiltration of the prostatic urethra by transitional cell carcinoma was found histologically but had not been appreciated with conventional cystoscopy or CT cystoscopy.
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In the cases of 14 patients, CT cystoscopy revealed no abnormality of the urinary bladder, and this finding was confirmed at conventional cystoscopy. These cases were considered true-negative findings. In two cases, CT cystoscopy had false-negative results. Two bladder tumors of polypoid morphologic features and a diameter less than 0.5 cm, one involving the vesical neck and the other a urinary bladder diverticulum, arising from the right urinary bladder wall were not identified, even at retrospective evaluation. In the latter case, the presence of blood clots interfered with the correct diagnosis.
Transverse, MPR, and virtual images proved complementary for lesion detection and localization. The combination of MPR images and virtual images facilitated detection of 11 tumors with a diameter of 0.5 cm or less not seen on axial images. Five of these lesions were seen on both MPR and virtual images, five only on virtual images (Fig. 6A, 6B, 6C), and one only on MPR images. MPR imaging facilitated evaluation of the extravesical extension of disease in five cases and evaluation of the extent of disease to the distal ureter in two cases (Fig. 7). Diagnostic results differed significantly (p = 0.013, McNemar test) between conventional cystoscopic and axial images. The difference was slightly significant (p = 0.065) for MPR images and was nonsignificant (p = 0.99) for virtual images. These results showed the advantage of virtual imaging over MPR imaging and especially over transverse imaging for lesion detection.
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Because tube current was modulated across the patient's body (dose modulation function), the mean tube charge per rotation was found to be 156 mAs on the basis of data collected from a small sample of consecutively imaged patients. The effective dose for the entire CT examination (supine and prone scanning) was 8 mSv.
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CT virtual cystoscopy allows imaging of the urinary bladder in multiple planes and a 360° view, which is not possible with conventional cystoscopy. With CT virtual cystoscopy, the radiologist acquires information about the location, size, and morphologic features of the lesions and conveys it to the surgeon performing cystoscopy, indicating appropriate areas for evaluation and biopsy. Urinary bladder tumors can be accurately measured and precisely localized before transurethral resection. CT virtual cystoscopy can be performed in cases in which conventional cystoscopy is not feasible, such as in the presence of urethral strictures, marked prostatic hypertrophy, or active bleeding, and in cases in which cystoscopic findings are inconclusive. CT virtual cystoscopy can be used to evaluate areas of the urinary bladder difficult to assess with cystoscopy, such as the anterior bladder neck and narrow-mouthed diverticula. Frank et al. [29] proposed the use of CT endoscopy in examinations of patients with bladder substitution. Those authors reported satisfactory results in evaluation not only of the neobladder but also of the antireflux nipple and afferent ileal limb and ureters. Finally, virtual cystos-copy depicts both intraluminal and extraluminal pathologic changes, so intravesical disease and extravesical extension can be evaluated in the same study.
CT virtual cystoscopy does have limitations. It has low sensitivity in the detection of small tumors. Narumi et al. [7] reported a sensitivity of 77% in identification of lesions smaller than 10 mm. Song et al. [9] reported a detection rate of 60% for tumors with a diameter of 0.5 cm or less. Yazgan et al. [17] and Nambirajan et al. [18] detected three of seven lesions and one of three lesions with a diameter smaller than 0.5 cm, respectively. These groups of investigators used a single-detector CT scanner and a collimation of 3 mm. They also used the shaded surface display technique for creation of virtual images. Two other studies [8, 10] were performed with a single-detector CT scanner, but the volume-rendering technique for creation of virtual images had better results in the detection of small tumors. In a study with 13 patients, Fenlon et al. [8] identified all 31 bladder lesions seen with conventional cystoscopy, including 19 lesions with a diameter smaller than 10 mm. Tsili et al. [10] detected all 30 bladder lesions in 24 patients. However, only four lesions less than 0.5 cm in diameter were included in this study.
The introduction of MDCT scanners has allowed use of thinner collimation, giving better results in the detection of small lesions. Merkle et al. [30], using a double-detector scanner and a slice thickness of 3.2 mm, identified all bladder tumors in a study that included 12 patients. This study, however, did not include tumors smaller than 0.5 cm. Arslan et al. [27], using 4-MDCT and a slice thickness of 1 mm, identified 10 of 11 bladder tumors in 18 patients. Two of the lesions had a diameter smaller than 0.5 cm. Using 4-MDCT and a slice thickness of 1.25 mm, Kim et al. [28] performed better in identification of small lesions. They reported a sensitivity of 88% (15 of 17 lesions) in the detection of lesions smaller than 0.5 cm.
Our study was one of the first to evaluate the utility of 16-MDCT cystoscopy in the detection of urinary bladder neoplasms. Our CT protocol enabled fast and detailed evaluation of the region of the urinary bladder with a short postprocessing time. The mean time to complete the whole CT cystoscopy procedure was 5 minutes, and the time for interpretation of the CT data, including acquisition and evaluation of the axial tomo-graphic slices, the MPR images, and the virtual cystoscopic images, was approximately 7 minutes. Fifty-five (96%) of 57 urinary bladder lesions proven at conventional cystoscopy were detected with MDCT cystos-copy in this study, including 18 lesions with a diameter of 0.5 cm or less, six of them sessile. These results are mainly attributed to the CT protocol used. Acquisition with thin collimation and the creation of MPR images with no artifacts and in excellent anatomic detail and of virtual images of very good quality facilitated detection of a large number of small tumors with a 16-MDCT scanner. Use of a 64-MDCT scanner further improves spatial resolution in the longitudinal direction with refined z-sampling techniques and therefore may improve the diagnostic performance of CT in the detection of lesions with a diameter smaller than 5 mm [22, 23]. The combination of dynamic contrast-enhanced imaging and virtual CT cystoscopy may further improve detection of bladder lesions, especially small, early, or flat tumors, because bladder neoplasms become more enhanced than adjacent normal wall [31].
The high rate of detection of malignant tumors of the urinary bladder in this study can be attributed to the use of the volume-rendering technique for creation of the virtual images. Volume-rendered algorithms [32] entail use of all of the CT data and therefore yield greater anatomic detail than does the shaded surface display technique. Furthermore, it has been shown [33] that mucosal detail is better on virtual endoscopic images obtained with the volume-rendering technique than on images obtained with surface rendering.
Our study showed that combined evaluation of axial, MPR, and virtual images should be used to increase the performance of the technique, especially in recognition of small tumors. Virtual imaging proved superior for lesion detection in our study, as it did in a study by Kim et al. [34] in comparison with virtual cystoscopy and MPR and axial source imaging in the detection of urinary bladder lesions. The limitations of axial scanning, namely axial noncontiguous bladder display and partial voluming of small tumors, are supervened with MPR and virtual images. In our study, use of MPR and virtual imaging enabled detection of 11 small tumors not seen on axial images. Virtual cystoscopy also enabled evaluation of large amounts of data, improving appreciation of 3D structures over that possible with 2D images. MPR imaging had satisfactory results in the assessment of extravesical extension of disease and of neoplastic involvement of the distal part of the ureters.
No clinically important complications were caused by CT cystoscopy in this study. To our knowledge, only one case of complication has been reported in the English literature, and that complication was related to catheter removal at CT cystoscopy. The absence of clinical sequelae confirmed the safety of the technique [9].
The achievement of significant differences in CT attenuation between the urinary bladder wall and the lumen is essential to acquisition of satisfactory virtual images. The use of air to distend the urinary bladder results in a high attenuation gradient between air and mucosa, producing ideal conditions for acquisition of virtual images [7]. Virtual CT cystoscopy of the air-filled bladder, as performed in this study, is inherently invasive because of catheterization. The use of a Foley catheter is associated with risk of infection, although minimal (1–2%) compared with that of conventional cystoscopy. Examining the patient in both supine and prone positions is another disadvantage, resulting in an increase in radiation dose. The effective dose for our CT protocol was 8 mSv. Nevertheless, radiation exposure is limited to the bladder area, and therefore it may not be considered an important issue. Further studies with low tube current–time settings are necessary to reduce the radiation risk. Low tube current–time settings for air-filled CT cystoscopy have been proven accurate in the detection of malignant tumors of the urinary bladder [10].
Because catheterization is not necessary, virtual CT cystoscopy after IV administration of iodinated contrast material is less invasive than the technique with an air-filled bladder and has been reported effective in depicting pathologic changes in the urinary bladder [18, 28, 30, 34, 35]. It also requires scanning in one position, so that the radiation dose can be halved compared with that used for virtual CT cystoscopy of an air-filled bladder. Virtual CT cystoscopy of a contrast material–filled bladder can be performed as part of a routine contrast-enhanced abdominal CT examination or as part of CT urography, enabling thorough evaluation of the entire urinary tract. Potential allergies to contrast media and inability to perform the technique on patients with renal insufficiency are limitations of the procedure. Another limitation of the technique is that the presence of artifacts on virtual images can degrade image quality if mixing of urine and contrast material is inadequate, especially in examinations of urinary bladders that have marked trabeculation [18, 28].
Virtual cystoscopy has a favorable learning curve because of the simple luminal structure and the small volume of the urinary bladder. In our study, an overall view of the urinary bladder was first obtained from a centrally placed observation point. The bladder wall was divided into six segments: anterior, posterior, superior, inferior, right, and left. A field of view of 120° applied to the vertical and horizontal planes was used to assess each segment and the vesical trigone with the ureteral orifices and internal urethral orifice. Once identified, an abnormality was evaluated in various projections with the magnification tool.
There were limitations to our study. There was a strong bias in patient selection because only patients in whom there was a high clinical suspicion of bladder malignancy underwent evaluation. This selection resulted in increased sensitivity for bladder lesion detection. Therefore, the results of this study do not prove the value of MDCT cystoscopy in the screening of patients presenting with painless hematuria. In addition, CT data interpretation was completed by two radiologists in consensus, and consensus readings may favor the more experienced reader over the other. In future studies, interobserver reliability must be addressed.
Despite advances in MDCT cystoscopy in the detection of urinary bladder tumors, limitations of the technique persist. CT cystos-copy gives no information about the color and texture of the bladder mucosa; therefore, it cannot be used to detect carcinoma in situ. This technique also does not produce tissue for histologic examination. For these reasons, at present CT cystoscopy cannot totally replace conventional cystoscopy.
This results of this study suggest high efficacy of 16-MDCT cystoscopy in the diagnosis of urinary bladder neoplasms in a selected high-risk population, showing an improved rate of detection of small tumors. These results may justify the value of the technique for future screening, primary diagnosis, and surveillance of bladder cancer. The high diagnostic performance of MDCT cystoscopy in the detection of malignant disease of the urinary bladder may obviate conventional cystoscopy if virtual cystoscopy has negative findings. At present, MDCT cystoscopy is indicated for examinations of patients for whom conventional cystoscopy is difficult to perform, contraindicated, or unsatisfactory in interpretation and as an adjuvant tool for evaluation of areas of the urinary bladder difficult to assess with conventional cystoscopy, such as the anterior bladder neck, the bladder base, and narrow-mouthed diverticula. MDCT cystoscopy can be useful for the long-term follow-up of patients with bladder tumors. Avoiding the invasiveness of conventional cystoscopy can be avoided while staging information is acquired. Prospective studies are needed to validate the role of MDCT virtual cystoscopy in the screening of patients presenting with painless hematuria.
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