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.