A Comparison Between the Effects of Paraffin and Plastic Embedding of the Normal and Obstructed Minipig Detrusor Muscle Using the Optical Dissector

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Abstract
The purpose of this study was to estimate the relative shrinkage of the normal, obstructed and recovery minipig urinary bladder by comparing tissues from the same bladders embedded in paraffin or plastic. Optical dissectors were used to make nucleus numerical density estimates in thick paraffin and plastic sections from the same bladder. The ratio of the 2 numerical densities depends only on differences in tissue shrinkage. In 9 minipigs a partial bladder outlet obstruction was created by implanting a 6 to 7 mm. Teflon ring 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. Biopsis were taken prior to obstruction, at removal of obstruction, and after recovery and were processed for paraffin and plastic sections to evaluate relative shrinkage. Two control pigs were sham-operated and biopsies taken at the same 3 time points. The optical dissector method was found to be an easy way to estimate the relative shrinkage of paraffin-embedded bladder tissue in proportion to plastic-embedded tissue. Both in human and minipig bladders, paraffin embedding caused a relative shrinkage of about 30 percent in proportion to plastic embedding. Both the obstructed and recovery detrusor muscles responded to embedding by either method in a manner indistinguishable from the normal bladder. When dealing with stereological evaluation of the detrusor muscle, the relative shrinkage of the embedded normal, obstructed and recovery bladder tissue can be ignored.