Main findings
Grossly, the vaginal outlet wall resembles a “belt-like” structure in
the vertical orientation when compared to the horizontal position of the
vaginal wall, Fig. 3. The vaginal walls’ distal edges fuse with the
vaginal outlet wall a) anteriorly — the inferior border of the
membraneous urethral sphincter; b) posteriorly — the fossa
navicularis; c) laterally — the perineal body extension and the labia
minora. The H/E histology examination confirmed these anatomical
findings. The vaginal hymeneal crease is visible and distinguishes those
two parts. The crease between the labia minora and the vaginal outlet
wall separates them and the fossa navicularis.
Microscopic characteristic features showed three strata of the vaginal
outlet wall: superficial (the hymeneal membrane), intermediate (the
hymeneal ring), and deep (the hymeneal plate), Fig. 2. These findings
verify the anatomical discovery of the vaginal outlet wall in the
present study, Fig. 1B, and Fig. 2. The superficial layer of the
vaginal outlet wall structure is the thin mucosal lining—the hymeneal
membrane, which consists of striated non-keratinizing squamous
epithelial cells arranged, on the average, in three roses. The basal
stratum is a single layer of columnar cells with scant cytoplasm
surrounding the oval and hyperchromatic nuclei. Additionally, there are
two roses of cuboid cells with centrally located, round, and
hyperchromatic nuclei. Directly beneath the squamous epithelium were
well-organized lamina propria with projecting papillae into the
overlying squamous epithelium and with connective fibers, the capillary
blood vessels network, and nerve endings. In addition, the parabasal,
basal cells, and basal lamina are present, Fig. 2.
The Intermediate layer — the hymeneal ring — of the vaginal
outlet wall is composed of dense connective avascular and aneural tissue
fibers with laguna cell aggregates and muscle fibers, Fig. 2. The
hymeneal ring presents itself grossly as anatomical cartilage, which
provides biomechanical tensile strength, tensile resistance strength,
and elasticity. This cartilage tissue within the hymeneal ring plays a
significant role in clinical obstetrics (tissues resistant during the
second stage of vaginal delivery) and gynecology (superficial
dyspareunia or entry dyspareunia, vaginal outlet stenosis, vulvar
vestibulitis syndrome.18-20
Finally, the hymeneal plate’s deep layer is the stratum of the
vaginal outlet wall composed of dense elastic, connective, and smooth
muscle fibers, Fig. 2. Longitudinal smooth muscles of the hymeneal plate
fuse with the vaginal wall muscular layer.
The MRI study showed the presence
of the vaginal outlet wall and termed it “the vaginal sphincteric
zone.” 4 The authors of this MRI clinical
investigation published their findings before the current anatomical
study. MRI description of the vaginal sphincteric zone documented the
existence of the vaginal outlet wall.