The bladder itself is made up of four layers. These layers are important landmarks in determining how deeply the tumor has invaded and the ultimate stage of the cancer.
Epithelium: The epithelium, which lines the bladder and is in contact with the urine, is referred as transitional epithelium or urothelium. Most bladder cancers originate from the cells of this transitional epithelium. The urethra, ureters and the pelvis of the kidney are also lined by this transitional epithelium, therefore, the same types of cancers seen in the bladder can also occur in these sites.
Lamina propria: Under the epithelium is the lamina propria, a layer of connective tissue and blood vessels. Within the lamina propria, there is a thin and often discontinuous layer of smooth muscle called the muscularis mucosae. This superficial layer of smooth muscle is not to be confused with the true muscular layer of the bladder called the muscularis propria or detrusor muscle.
Muscularis propria or detrusor muscle: This deep muscle layer consists of thick smooth muscle bundles that form the wall of the bladder. For purposes of staging bladder cancer, the muscularis propria has been divided into a superficial (inner) half and a deep (outer) half.
Perivesical soft tissue: This outermost layer consists of fat, fibrous tissue and blood vessels. When the tumor reaches this layer, it is considered out of the bladder.
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