Parietal pelvic fascia
The parietal pelvic fascia (fascia pelvis parietalis) acts as the internal lining of the lesser pelvis. It closely covers the parietal muscles as well as the pelvic floor musculature.
- Muscle coverage: the fascia overlies the piriformis muscle (m. piriformis), obturator internus muscle (m. obturatorius internus), and coccygeus muscle (m. coccygeus). It also covers the levator ani muscle (m. levator ani) and the deep transverse perineal muscle (m. transversus perinei profundus).
- Fixation and thickness features: the layer is firmly fused with the inferior rami of the pubic and ischial bones. However, its density is uneven: maximum thickness and strength are observed in the area of the m. obturatorius internus, whereas over the m. piriformis and m. coccygeus the fascia becomes significantly thinner.
- Arcus tendineus fasciae pelvis (arcus tendineus fasciae pelvis): represents a prominent thickening of the parietal layer. This dense band stretches from the pubic symphysis to the ischial spine and serves as the origin site for the m. levator ani.
Fasciae of the pelvic and urogenital diaphragms
The topography of the fasciae is closely related to the muscles forming the pelvic floor.
Relationship to the pelvic diaphragm: The levator ani muscle (m. levator ani) is enclosed in a distinct sheath. It is covered superiorly by the superior fascia of the pelvic diaphragm (fascia diaphragmatis pelvis superior) and inferiorly by the inferior fascia (fascia diaphragmatis pelvis inferior). Both of these plates extend laterally and fuse with the arcus tendineus fasciae pelvis. Clinical significance: the fusion of the fasciae with the tendinous arch is loose. This creates the anatomical prerequisite for the subperitoneal pelvic fat to communicate with the perineal fat (specifically, the ischioanal fossa). It is precisely along this pathway that abscesses drain and spread from the lesser pelvis cavity.
Relationship to the urogenital diaphragm: The deep transverse perineal muscle (m. transversus perinei profundus) also has a double-sided covering. The superior and inferior fasciae of the urogenital diaphragm (fascia diaphragmatis urogenitalis superior et inferior) enclose the muscle on the respective sides. At the anterior edge of this muscle, both layers firmly fuse with each other, forming the transverse perineal ligament (lig. transversum perinei).
Visceral pelvic fascia and its extensions
The visceral pelvic fascia (fascia pelvis visceralis) is designed to isolate the organs. It forms an individual enclosed receptacle (capsule) for each lesser pelvis organ. The organs lie medially and do not come into contact with the osteomuscular walls of the pelvis, as they are separated from them by a layer of loose fatty tissue through which nourishing vessels and nerves run.
For additional organ fixation, the fascia forms specialized extensions:
- Sagittal extensions: originate anteriorly from the medial margin of the internal opening of the obturator canal. They course from anterior to posterior, fusing along the way with the capsules of the urinary bladder and rectum. The extensions terminate by attaching to the anterior surface of the sacrum (near the sacroiliac joint). Visceral branches of blood vessels and nerves to the pelvic organs pass within the thickness of these extensions.
- Rectovesical/rectovaginal septum (fascia of Denonvilliers): located in the frontal plane. In males, this structure separates the urinary bladder with the prostate gland anteriorly from the rectum posteriorly. In females, the septum runs between the vagina and the rectum. At the margins, it fuses with the sagittal extensions and also reaches the sacrum.
Briefly: answers to topical questions
Which specific blood vessels and nerves run within the thickness of the sagittal extensions of the visceral pelvic fascia?
Within the thickness of the sagittal extensions of the visceral pelvic fascia run visceral branches of vessels and nerves that supply blood to and innervate the lesser pelvis organs.
The specific names of the blood vessels and nerve trunks are not detailed in the presented materials; only their general functional purpose is indicated:
- Contents of the sagittal extensions — visceral branches of vessels and nerves to the pelvic organs.
To avoid confusing the layers, use a room analogy: the parietal fascia is like "wallpaper" glued tightly to the walls and floor (pelvic muscles), while the visceral fascia is like "covers" fitted over the furniture (organs) sitting in the center of the room. The space between them is filled with loose fatty tissue containing "wires" (vessels and nerves).
Class and exam questions
What is the source of the formation of the pelvic fascia?
The pelvic fascia is formed as a direct continuation of the extraperitoneal fascia (endopelvic fascia) as it transitions into the pelvic cavity.
Where is the parietal fascia thickest?
The parietal fascia is most prominent and thickened in the area of the obturator internus muscle (m. obturatorius internus). Over the piriformis and coccygeus muscles, it is significantly thinner.
What is the role of the loose fusion between the pelvic diaphragm fasciae and the tendinous arch?
This weak spot allows the subperitoneal fat to communicate with the ischioanal fossa, which serves as a pathway for the spread and drainage of lesser pelvis abscesses.
How is the transverse perineal ligament formed?
It is formed as a result of the tight fusion of the superior and inferior fasciae of the urogenital diaphragm at the anterior edge of the deep transverse perineal muscle.
What else to study on this topic
- Topography and clinical significance of the arcus tendineus fasciae pelvis (arcus tendineus fasciae pelvis).
- Anatomy of the sagittal extensions: course, fixation, and neurovascular contents.
- Sexual dimorphism in the localization of the rectovesical/rectovaginal septum.
- Mechanisms of capsule formation for pelvic organs by the visceral fascial layer.
- Pathways of communication between the fascial spaces of the lesser pelvis and the perineum.
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