Histology
Histology of the excised vaginal outlet biopsy showed no perineal skeletal muscle present in the excised specimens and verified three distinctive layers: the hymeneal membrane, ring, and plate, Fig. 1C. The absence of the perineal muscle within the excised V-shape tissue from the vaginal outlet wall helps understand the mechanism of perineal postpartum pain and later, occurrences of superficial dyspareunia. Therefore, the present study shows that the posterior perineal musculature is unnecessary to cut to widen the vaginal outlet during fetal delivery.
The current anatomical research demonstrated that the vaginal outlet wall was not the extension of the vaginal walls but a separate anatomical structure with characteristic histological features connected to the vaginal wall, Fig. 1, B, 2. Furthermore, the vaginal outlet gets thinner, progressing from the thick posterior to the thin anterior vaginal wall’s edges. These anatomical findings help determine where to place an incision when an obstetrical episiotomy procedure is performed or how to reconstruct the defective vaginal outlet wall. The vaginal outlet wall is the narrowest part of the vaginal canal. This finding may play a significant role during the fetal head vaginal delivery because it creates tissue resistance by the hymeneal ring cartilage on passing through a fetal head, Fig. 3B.