STUDIES ON METAPLASIA OF THE BLADDER EPITHELIUM IN PARAPLEGIA

The normal transitional epithelium of the urinary bladder is histopathologically situated between the squamous cell with lower differentiation and the columnar cell with higher differentiation. In relation to this notion, the author has attempted to raise the following hypothesis.The epithelium of the bladder, under long-term stess such as chronic infection and physical or chemical stimuli, tends to cause metaplasia in the process of regeneration of injured epithelial tissue, for a better protection of the original epithelium, depending on its environmental situation. The direction of this metaplasia could be towards either squamous or columnar, and these two directions could also be present independently or together in combination. And it would be the bladder epithelium itself that determined the direction of metaplasia, in order to be protected better in each situation. The epithelium, in which metaplasia has once developed, has already started to proceed into the progressive cell-division towards abnormal direction, with a possibility either of continuing its stable activity of metaplasia or growing into a critical condition such as malignant alteration.Bearing this hypothesis in mind, the author carried out histopathological studies of the bladder epithelium in 154 cases of paraplegia, with use of the specimens such as the cytologic smears of the urine and the tissues of the bladder neck obtained at biopsy and autopsy.The significant findings in these studies were summarized in the followings.1) In the smeras of the urine, developement of metaplasia with squamous epithelium was found in 85 cases (64%) among 134 cases examined.2) In the biopsied specimens from the bladder-neck, squamous metaplasia was also found in 25 cases (73.5%) among 34 cases.3) The finding described in 1) and 2) were considered not to be related with the severity of the urinary-tract infection accompanied.The developent of squamous metaplasia was estimated to be about 5-6 months after the onset of paraplegia when urinary tract infection was accompanied.4) In the postmortem examination of the urinary bladder in 21 cases of paraplegia, 6 cases had squamous metaplasia, 1 case had partially columnar metaplasia, and 4 cases had bladder carcinoma in which squamous cell carcinoma was found in 3 cases.The finding that squamous cell carcinoma developed predominantly in the bladder in cases of paraplegsia is considered to be in contrast to the fact that occurrence of adenocarcinoma was observed predominantly in cases of bladder exstrophy, similarly accompanied with chronic infection, being exposed to physical or chemical stimuli for a long period.It is thus conceivable that the bladder epithelium in cases of paraplegia, under chronic stimuli of infection, has, in its process of regeneration, some difficulty to proceed into its original transitional epithelium, and rather tends to regenerate into squamous cell metaplasia for a protecting effect, and finally to progress into malignancy as squamous cell carcinoma when some unknown cancer-producing factors are additionally involved in these situations.It is also suggested that long-lasting stimuli such as chronic urinary-tract infection and foreign bodies are playing very important roles in cases of paraplegia, in the process of regenerative changes of the injured normal bladder epithelium into squamous metaplasia, and even further into neoplasm.