الفهرس 
Ayman Mohamed IbraHImOnly 14 pages are availabe for public view
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Abstract
C
arcinoma of the urinary bladder is one of the most common urothelial neoplasms. It has high rates of recurrence at the initial tumor site and elsewhere throughout the transitional epithelium. Gross painless hematuria is the classic clinical sign of bladder carcinoma. It has the highest lifetime treatment costs per patient of all cancers.
Many imaging modalities including CT, trans-abdominal US, cystography, IVU, and MR imaging were used to evaluate the bladder.
Conventional cystoscopy remains in the clinical use the standard for evaluation of the bladder for neoplasms and may be a necessary in patients suspected of having bladder carcinoma as it has the ability of taking biopsy from suspected lesions .
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.
Urinary bladder is an appropriate organ for virtual endoscopy because of its simple luminal morphology, its relatively small volume and the absence of involuntary peristalsis.
CTVC technique is of a great value in detection of bladder tumors larger than 5 mm with high sensitivity, specificity and accuracy rates.
Two techniques have been used for virtual cystoscopy, either air or contrast material to fill the bladder. Virtual cystoscopy of the air-filled bladder is invasive because catheterization is required to introduce air into the bladder. Catheterization is uncomfortable and is difficult to use in cases of stricture of the urethra; however, catheterization is not required for virtual cystoscopy of the contrast materialfilled bladder because it can be performed as a part of the routine abdominopelvic intravenous contrast-enhanced CT examination. Additionally, the radiation dose in the former method is doubled: virtual cystoscopy of air-filled bladders requires two sets of CT data obtained with the patient in supine and prone positions, whereas contrast material-filled virtual cystoscopy data are obtained only once. One possible complication of the air-filled method is the introduction of infection due to the use of room air. However, virtual cystoscopy with contrast material-filled bladders may be limited by a risk of contrast-induced reactions and nephrotoxicity.
As a minimally invasive procedure, virtual cystoscopy provides many advantages. It allows accurate localization of a lesion due to its wide field of view. 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 urethral stricture or marked prostatic hypertrophy, who may be poor candidates for conventional cystoscopy, can safely undergo virtual cystoscopy, since a small urethral catheter can be used to instill air into the bladder, Use of the transverse images during CT cystoscopy also allows for comprehensive pelvic imaging to assess extravesical metastases.
Additionally, because CT virtual cystoscopy allows imaging of the urinary bladder in multiple planes, it can be used for the evaluation of areas of the urinary bladder that are difficult to assess with conventional cystoscopy such as bladder neck, trabeculations and diverticulae . 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 neighbouring organs.
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. Another limitation is that it 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 we face a similar problem because biopsy is often required to determine whether a bladder lesion is inflammatory, fibrotic, or neoplastic. The calcifications associated are seen only on the transverse images and not on the virtual images. False-positive finding of lesion may be reported due to air bubble in bladder. Many artifacts were also reported in technique of CTVC of the contrast material- filled bladder when urine and contrast could not be mixed properly.
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.
Of special interest is the technique of color mapping, which may optically facilitate distinction between normal and pathologic conditions.
Virtual Cystoscopy with color mapping contributes more comprehensive informations, because it is not restricted to the surface and takes changes of the entire wall thickness into account.
Tumors, benign wall thickening and normal wall thickness are correctly identified by using axial source images and virtual cystoscopy with color mapping. The 3D models with color mapping are excellent at indicating how far tumors had infiltrated. However, the color mapping is sensitive to artifacts.
On the other hand several disadvantages were reported regarding CTVC, although areas of wall thickening are seen on virtual images, they are more conspicuous on the transverse views.
Recently high sensitivity rates for detection of bladder lesions less than 5 mm by VC have been reported by many authors.