A COMPARISON BETWEEN THE EFFECTS OF PARAFFIN AND PLASTIC EMBEDDING OFTHE NORMAL AND OBSTRUCTED MINIPIG DETRUSOR MUSCLE USING THE OPTICAL DISSECTOR

Purpose: The purpose of this study was to estimate the relative shrink age of the normal, obstructed and recovery minipig urinary bladder by comparing tissues from the same bladders embedded in paraffin or plast ic. Materials and Methods: Optical dissectors were used to make nucleu s numerical density estimates in thick paraffin and plastic sections f rom the same bladder. The ratio of the 2 numerical densities depends o nly on differences in tissue shrinkage. In 9 minipigs a partial bladde r outlet obstruction was created by implanting a 6 to 7 mm. Teflon rin g around the proximal urethra. After an obstruction period (median 63 days) the ring was removed and after a recovery period (median 60 days ) the animals were sacrificed. Biopsies were taken prior to obstructio n, at removal of obstruction, and after recovery and were processed fo r paraffin and plastic sections to evaluate relative shrinkage. Two co ntrol pigs were sham-operated and biopsies taken at the same 3 time po ints. Results: The optical dissector method was found to be an easy wa y to estimate the relative shrinkage of paraffin-embedded bladder tiss ue in proportion to plastic-embedded tissue. Both in human and minipig bladders, paraffin embedding caused a relative shrinkage of about 30% in proportion to plastic embedding. Both the obstructed and recovery detrusor muscles responded to embedding by either method in a manner i ndistinguishable from the normal bladder. Conclusion: When dealing wit h stereological evaluation of the detrusor muscle, the relative shrink age of the embedded normal, obstructed and recovery bladder tissue can be ignored.