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.