Surgical anatomy of the perineal muscles and their role in perineal disorders.

The anterior perineum contains the perineal body and muscles. It is the site of functional and pathological disorders, many of which have not yet been related to a precise cause. In the present study, we investigated the anatomy of the perineal muscles with the aim of elucidating their function in light of their anatomic structure. Knowledge of their functional-structural relationship is deemed necessary for the understanding of the disorders that affect this part of the perineum. The perineal muscles of 28 cadaveric specimens were studied by direct dissection, as well as histologically. Fifteen male and 13 female specimens were collected from 18 adult (mean (+/- SD) age 31.6 +/- 9.8 years) and 10 neonate cadavers. Histological sections were stained with hematoxylin and eosin and Masson's trichrome stain. The fibers of the superficial transverse perineal muscle proceeded medially to decussate in a criss-cross pattern with the muscle fibers of the contralateral muscle; a few muscle fibers passed directly without decussation. Similarly, the fibers of the deep transverse perineal muscle decussated with their fellows on the opposite side. The two decussation raphes constituted the main bulk of the perineal body. A 'digastric' pattern could be identified for each of the superficial transverse perineal muscle and deep transverse perineal muscle. This pattern allows simultaneous contraction of the muscles on both sides as a single unit. The perineal muscles, forming the floor of the anterior perineum, are apparently subjected to variations in intra-abdominal pressure, which, if exceeding normal physiological limits, may lead to weakening, subluxation and sagging of the perineal muscles and, eventually, to perineocele. Further studies to investigate the role of the perineal muscles in the functional disorders of the perineum are needed.