Pathophysiology of Radiation Injury
Studies of radiation-induced bladder injury in animal models have been essential in expanding our knowledge on the pathophysiology of radiation injury. Various techniques, including measurement of urinary frequency, bladder compliance, cystometry and histologic examination of irradiated bladder tissue, have been utilized to determine radiation-induced changes that can occur in the bladder wall and their effects on bladder function.7,8,9,10,11,12,13,14–15 Studies in mice demonstrate the murine bladder has a triphasic response to radiation. The early, or acute phase, starts during radiation exposure and resolves several weeks after radiation is complete. This is followed by a latent period, which is time dependent on the amount of dose received. Finally, there is a progressive, irreversible late phase, where reduction in bladder storage capacity leads to symptoms of urgency and increased frequency. It is hypothesized that the human bladder also responds to radiation in a triphasic pattern. In humans, the late phase can occur up to 10 years after initial radiation exposure.16,17 The pathophysiology behind the early and late effects of radiation on the bladder has not been fully delineated, but what we have learned from animal studies is summarized below.
The urothelium acts as a protective barrier that allows urine to be stored for long periods of time while maintaining initial composition. Viewed in cross section, the urothelium is composed of three main layers: basal, intermediate, and superficial (Fig. 32.3). When the urothelial barrier ...
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