Macroscopical and histological characterization of the perineal membrane and deep perineal pouch

The existence of a striated deep transverse perineal (DTP) muscle remains an ongoing debate. We hypothesize that the DTP is macroscopically and microscopically detectable as a definable striated muscle belly in elderly males, but not in elderly female donors used in the dissection course. Investigations were performed on embalmed human donors of both sexes (n = 10, mean age at death: 82 years). We dissected the ischioanal fossa. After removing all the loose fat and connective tissues, including the arteries and nerves, we exposed the compact transversally running plate-shaped tissue stretched between the ischiopubic rami. Additionally, we removed the ischiocavernosus and bulbospongiosus muscles in the superficial perineal pouch along with the external genitals. The entire tissue plate located in the deep perineal pouch was then detached from the surrounding bony structures and dissected. To verify the musculature and its striation, we analyzed the tissue stereologically using light microscopy. At 40 μm intervals, 4-μm-thick serial sections were made perpendicular to the surface of the dissected tissue block. We determined the volume densities of the connective tissue, smooth muscle cells, and striated muscle fibers in the selected sections relative to the entire tissue in the deep perineal pouch. A relatively thick tissue plate (diameter: 4-5 mm) located superior to a fascia-like structure, the perineal membrane, was observed running transversally to the ischiopubic rami. Macroscopically, a clearly visible transverse running muscle was not observed in both sexes. Histologically, serial sections showed that the samples mainly consisted of connective tissue. In both sexes, the volume densities of the connective tissue were approximately 80%. In females, the volume density of the muscle cells was approximately 20%. In males, about 10% of the tissue was smooth, whereas just over 10% was striated muscle. However, the standard deviation between the donors was remarkable. In females, the proportion of the striated muscle cells was less than 1%. With increasing age, the volume density of the connective tissue increased, whereas those of the smooth muscle cells and/or striated muscle fibers decreased, independent of sex. There was no evidence of the existence of a clearly definable striated DTP muscle, not only in females but also in males. Muscle cells decreased with increasing age.