Intravesical Ultrasonography for Tumor Staging in an Orthotopically Implanted Rat Model of Bladder Cancer

Purpose: Noninvasive and serial evaluation of tumor development and growth is important in an orthotopic animal bladder tumor model. However, to our knowledge a reliable method has not been established. We determined the usefulness of intravesical ultrasonography for tumor staging and volumetric assessment in an animal model. Materials and Methods: Tumors with various stages were formed in 20 female Fischer F344 rats by implanting AY-27 rat bladder carcinoma cells. Cells were implanted by instilling a suspension (4 × 10⁶ cells) into the bladder cavity after urothelial denudation using hydrochloric acid or by directly injecting the cell suspension into the bladder wall. Tumor volume and invasion depth were measured by intravesical ultrasonography using an ultrathin 2.5Fr intraluminal ultrasound catheter via the urethra 7 to 10 days after cancer cell implantation. The rats were then sacrificed for histopathological examination. Results: All rats showed bladder tumors 7 to 10 days after cancer cell implantation, of which stages varied from superficial to advanced disease. Intravesical ultrasonography showed a clear cross-sectional view of all layers of the bladder wall and enabled visualization of bladder tumors (minimal 0.5 mm in diameter). This approach also provided an accurate diagnosis of tumor invasion into muscle layers and perivesical tissues with precise invasion depth and tumor size. The positive predictive ratio regarding tumor staging reached 85%. Repeat examinations were feasible without noticeable adverse effects. Conclusions: Intravesical ultrasonography is a reliable and appropriate noninvasive method for evaluating tumor stage and size in an orthotopic rat bladder tumor model.