Painless hematuria is one of the typical signs of bladder cancer, and one of the most important problems with urinary bladder tumors is disease recurrence. Therefore, close monitoring of the patient is required .
CT is the usually recommended radiologic approach to assess hematuria, and for CT to depict even small bladder lesions, optimal imaging conditions including adequate bladder distention and thin-slice scanning must be fulfilled .
According to Cohan et al. 2009, small urinary bladder lesions that are located at the bladder base (near the prostate and urethra) are difficult or impossible to be distinguished from prostatic enlargement or periurethral tissue. Accordingly, in patients with hematuria, negative findings on CT warrant performance of conventional cystoscopy .
For assessing the urinary bladder tumors, the gold-standard of current diagnosis, as well as follow-up is the rigid/flexible cystoscopy . Patients with urinary bladder masses should undergo interval cystoscopy to detect disease recurrence which is recommended at 3 months intervals for the first year, 6 months for the second year and annually thereafter .
The most significant problems encountered in conventional cystoscopy are the intense discomfort for the patient and bleeding; furthermore, the high cost, invasive nature, and local complications such as infections. Additionally, conventional cystoscopy does not provide information about extravesical extension of the tumor .
Urinary bladder may be an ideal intra-abdominal organ for virtual endoscopic navigation because of its simple luminal morphology, its small volume and the absence of peristalsis . In this study, we tried to assess the utility of virtual cystoscopy in diagnosis of new and recurrent bladder tumors compared to conventional cystoscopy.
Fletcher and Luboldt, 2000 pointed out that the higher resolution inherent to CT, results in a better quality of the endoluminal view. And that is why the introduction of multidetector CT (MDCT) scanners was a major technologic advance because it substantially improved z-axis (longitudinal) resolution by reducing section collimation and facilitating detection of very small lesions [11, 12].
In our study, we used the volume rendering technique for image processing, this was in agreement with most of the authors who preferred using this technique which provides an excellent mucosal and lesion details.
The results of Hopper et al. 2000 study strongly support volume rendering for CT virtual reality, with the transition zone (mucosa) reconstructed as a separate structure .
Also Allan, 2001 and Tsampolus et al. 2008 found that the use of volume rendering algorithms provides a more accurate representation of tissue morphology than surface-shaded display as volume rendered images are data-rich using all available computed tomography data for reconstruction and the resultant images having fewer smoothing and blurring artifacts and this will help detecting more small lesions [14, 15].
In our study, 25 out of 38 (65.7%) of bladder lesions were transitional cell carcinoma, squamous cell carcinoma ranked second (8 out of 38; 21%), followed by benign inflammatory lesions (4 out of 38; 10.5%) and blood clot (hematoma) (1 out of 38; 2.6%). Moreover, there were 7 cases (23.3%) with history of bilharziasis among the 30 cases included in our study.
The results of previous studies stated that virtual cystoscopy allows the accurate assessment of localization and morphology of bladder masses [2, 15].
In our work, CTVC detected 9 out of 10 polypoid masses detected by conventional cystoscopy (90% sensitivity), 23 out of 23 sessile masses (100% sensitivity), 4 out of 4 areas of wall thickening (100% sensitivity), 0 out of 1 case mucosal color change (0 % sensitivity).
Concerning the size of the mass, two studies by Kim et al. 2002 and Tsili et al. 2004 were performed with a single-detector CT scanner, and a volume-rendering technique for creation of virtual images was used. The first study found that 15 (88%) out of 17 lesions smaller than 0.5 cm at conventional cystoscopy, were detected on virtual cystoscopy .
In the second study, all bladder lesions (30) seen on conventional cystoscopy were detected on CT virtual cystoscopy (CTVC), including four patients with lesions smaller than 5 mm .
Sixtenn multi-detector CT (MDCT) cystoscopy was used in Tsampoulas et al. 2008 study to detect urinary bladder neoplasms. Fifty-five (96%) of 57 lesions proven at conventional cystoscopy were detected, including 18 lesions with a diameter of 0.5 cm or less .
Teama et al. 2014 in their study used 64 MDCT and could identify (11/12) intravesical masses (less than 5 mm) .
In our study, 16 MDCT and 320 MDCT were used, 36 out of 38 lesions were detected with sensitivity about (94.7%) and specificity (100%), there were 2 missed lesions (1 of less than 5 mm size and the other was a mucosal color change), 3 of those 38 lesions were 5 mm or less (2 could be detected by VC) and were all proved with conventional cystoscopy.
Tsili et al. 2004 found that combining evaluated virtual images with axial and MPR images could provide valuable information for extraluminal disease, such as extravesical invasion, distal ureteral obstruction, and pressure of the neighboring organs .
Kim et al. 2005 concluded that virtual cystoscopy has many advantages over axial CT and MPR images. First, virtual cystoscopy is superior in evaluation of the mucosal surface of the bladder and therefore can detect superficial lesions missed by source CT images or MPR images. Virtual cystoscopy can help the operator to navigate the mucosal surface in various projections. Also, virtual cystoscopy provides interactive navigation, allowing the operator to make more confident decisions .
In our study, it was crucial to depend on both 2D and 3D images together for interpretation of virtual cystoscopy.
Many authors encouraging VC to be used as screening tests for patients with history of bladder tumor.
Tsili et al. 2004 said that the technique can be proposed as a screening test for recurrent bladder cancer. A negative CT cystoscopy would limit the need for conventional cystoscopy .
Kawai et al. 2004 agreed that VC is a useful screening tool which can direct the surgeon to an appropriate area for biopsy. If normal, it may obviate the need for conventional cystoscopy and biopsy, and could be useful for surveillance of known tumors .
In our study, 7 patients with history of TURT were included 1 recurrent polyp, 2 sessile masses, 1 wall thickening, and 4 patients were free, and all were confirmed by conventional cystoscopy.
Advantages of virtual cystoscopy noticed in our study include that the technique is non- or minimally invasive, with minimal discomfort and risks for the patients, especially that there is no need for anesthesia.
Virtual cystoscopy allows accurate measurement of the dimensions of the tumor with high accuracy in detection of bladder lesions, despite its size and morphology, as well as wall thickening.
Virtual CT cystoscopy improves the value of axial CT images and allows utilization of the largest amount of CT data as combined multiplanar and virtual cystoscopy depicts both intraluminal and extraluminal pathologic changes in the same study.
CT virtual cystoscopy also helps to assess urinary bladder areas that are difficult to be assessed using conventional cystoscopy, such as the anterior bladder neck and narrow-mouthed diverticulae.
The drawbacks we met in our study include that the partially calcified masses or bladder calculi were seen only on the source images but not on virtual images due to the threshold selection optimized to depict soft tissue abnormalities.
Another disadvantage is that virtual images alone cannot make sure of the nature, or the origin of the mass either it is vesical or extravesical like enlarged median lobe of the prostate.
Also the depth of the bladder wall invasion and the exophytic components could not be diagnosed unless CT virtual cystoscopy and MPR images were used together.
Six patients had paravesical fat extension, one patient had sigmoid colon invasion and two patients had seminal vesicles and prostatic invasion, virtual cystoscopy alone cannot judge the paravesical fat nor the surrounding structures invasion, and this was important criteria in grading the bladder tumor.
CTVC is unable to detect flat lesions, which appear as subtle color changes of the mucosa on conventional cystoscopy; therefore, it cannot be used to detect carcinomas in situ.
Moreover, CTVC lacks the ability to take tissue biopsy for histopathologic assessment; an ability that is possible on conventional cystoscopy.
The differentiation between small tumors and inflammatory swelling of the mucosa could be difficult, especially in patients with unsatisfactory bladder filling. There was a patient with a minute polyp diagnosed as inflammatory lesion after CC and biopsy.
In addition, fibrosis induced mucosal thickening cannot be distinguished from a neoplasm. Similar problem is faced in conventional cystoscopy, because biopsy is often required to determine whether a bladder lesion is inflammatory, fibrotic, or neoplastic.