Perineum: What is it? Limits, Content, Perineal Musculature, Innervations and Clinical Relevance

It is the anatomical region located between the thighs, in the lower part of the diaphragm of the pelvis, and constitutes the lower part of the pelvic outlet.

The perineum is separated from the pelvic cavity by the pelvic floor at the top.

In this region are contained the structures that support the urogenital and gastrointestinal systems of the human being.

Consequently, this structure plays a vital role in some functions of the organism, such as urination, defecation, sexual relations, and childbirth.

The perineum is the floor of the pelvis, and its muscular system is responsible for closing or covering the lower part of the entire pelvic cavity.

The perineum is this region between the thighs in the lower part of the pelvic diaphragm. The boundaries of this region are the pubic symphysis, the coccyx, the ischiopubic branches, and the sacrotuberous ligaments.

The perineum has a roof of the pelvic diaphragm and a floor of the fascia and the skin.

 

It also has the muscles and neurovasculature associated with the urogenital systems and the anus.

Limits

When described in clinical practice, the term “perineum” refers to the area between the external genitalia and the anus.

However, in anatomical terms, the perineum is made up of a diamond-shaped structure located at the bottom of the pelvis.

There are two ways in which the limits of the perineum can be represented.

When these limits are referred to as the anatomical borders, the exact bone margins are described.

Similarly, when referring to the edges of the surface, the anatomy of the perineum surface is described.

Anatomical borders:

The anatomical limits of the perineum are the following:

  • Previous limits, the pubic symphysis.
  • Limitations of the posterior end, the coccyx.
  • Anterolateral limits, lower ischial branches.
  • Posterolateral limit, the sacrotuberous ligament.
  • Lateral border, ischial tuberosities.
  • Ceiling, the pelvic floor.
  • Base, skin, and fascia.

The perineum is subdivided by tracing an imaginary line transversely between the ischial tuberosities.

This line forms two triangles: the anterior urogenital and the posterior anal triangles.

These deltas are significantly associated with the various components of the perineum.

Surface edges:

The limits of the edges of the surface are best presented when the lower limbs are moved away, and the perineum is represented as a large diamond:

  • The previous limit is the mount of Venus or pubis in females and the base of the penis in males.
  • Lateral limit, the middle surfaces of the thighs.
  • The posterior – upper end of the groove is located in the interlude.

Content of the triangle

When subdivided by the imaginary line between the ischial tuberosities, it forms the anterior urogenital and posterior anal triangles.

These triangles are associated with different components of the perineum, such as:

Anal triangle:

The anal triangle represents the posterior half of the perineum.

And it is delimited by the coccyx and sacrotuberous ligaments in addition to the imaginary line between the ischial tuberosities.

If we remove the skin and superficial fascia, we can see the anus located in the midline and two areas full of fat close to the anus, filling the space of the ischiorectal fossa called the yellow.

The main areas contained in the anal triangle are:

  • The anal opening.
  • The external muscle of the anal sphincter is the voluntary muscle whose function is to open and close the anus.
  • The levator ani muscle.
  • The internal obturator muscle.
  • The ischioanal pits are the spaces located laterally to the anus.

The anus is located in the center of the triangle, with an ischioanal fossa on each side.

The pits are formed by fat and connective tissue, which allows the anal canal to expand during defecation.

This extends from the lower part, the skin of the anal region, to the pelvic diaphragm on its upper part.

Urogenital Triangle:

The urogenital triangle is located in the anterior half of the perineum.

Its limits are the ischiopubic branches, the pubic symphysis, and an imaginary line between the two ischial tuberosities.

This triangle is associated with structures present in the urogenital system that is very complex, composed of several pouches and fascial layers.

The difference between the anal triangle and the urogenital triangle lies in an additional layer of fascia that is deep and strong, better known as the perineal membrane.

This membrane has several bags on the upper and lower surface. These layers or bags of the urogenital triangle are:

The deep perineal pouch is the space between the deep fascia in the pelvic floor in the upper part and the perineal membrane in the lower leg. Here is the urethra, the external urethral sphincter, and the vagina of the woman.

In the case of men, here are contained the urethral bulb glands and the deep, transverse perineal muscles.

The perineal membrane: It is a layer of fascia very resistant and perforated by the urethra and the vagina when it talks about the woman. The function of this membrane is to provide a compliment for the muscles of the external genitalia.

The superficial perineal pouch: It is the potential space between the perineal membrane of the upper part and the superficial perineal fascia of the lower leg.

This bag contains all the erectile tissues that make up the penis and the clitoris, as well as three muscles such as the ischiocavernosus muscle, the bulbs-sponges muscle, the transverse and superficial perineal muscles, and the Bartholin glands.

The perineal fascia is an extension of the abdominal fascia and has two components. The deep fascia is the one that covers the protruding structures such as the penis, the clitoris, and the superficial perineal muscles.

The superficial fascia of Camper: It is the one that is located under the skin in the urogenital triangle. The first identified is the fascia of the Scarpa or fascia of the Colles of the anterior abdominal wall. This fascia is firmly attached to the ischiopubic branch, located along the side of the urogenital triangle.

The skin: Where the urethral and vaginal orifices open.

Vascularization of the perineum

The internal pudendal artery is one of the branches of the internal iliac artery.

On the way, this artery passes through the sciatic spaces, also through the Alcok canal, and continues through the ischioanal fossa to the anterior triangle, accompanied by homonymous veins and nerves.

The irrigation branches of the internal pudendal artery are the following:

  • The lower rectal.
  • The perineal arteries.
  • The urethral arteries.
  • The urethral bulb arteries.
  • The components that go to the penis and the clitoris.

The external pudendal artery is a direct branch of the femoral artery that irrigates the skin of the vulva, both the labia minora and the labia minora, and the scrotum.

The veins follow the same path; these are the internal pudendal vein that ends in the internal iliac vein and the external pudendal vein that flows into the vein. Femoral.

The perineal body

The perineal body is composed of a very irregular fibromuscular mass. It is located at the junction of the two triangles, the urogenital and the anal, the central point of the perineum.

Skeletal muscles, smooth muscles, collagen, and elastic fibers are observed in this structure.

In women, it acts as a rupturing body between the vagina and the external anal sphincter, supporting the posterior part of the vaginal wall against prolapse.

In the male, it is between the penis and the anus bulb.

The pelvic diaphragm is composed of:

The levator ani muscle has three fascicles:

  1. The puborectal fascicle: That has a fundamental role in maintaining fecal continence.
  2. The pubococcygeal cluster: Is formed by the middle portion of the levator ani.
  3. The ileococcygeal fascicle: It is the posterolateral portion of the levator ani.

These fascicles are innervated by the coccygeal loop (S4 and S5).

The ischecoxigeal or coccygeal muscle:

This muscle resembles a triangular lamina and is located posterior to the levator ani muscle and unfolds from the sciatic spine to the sacrum and coccyx. Its function is to close the perineal region on its back and strengthen the pelvic floor.

The pyramidal muscle of the pelvis: This passes through the greater sciatic foramen and is one of the stabilizing muscles of the hip.

The internal obturator muscle: It is the one that covers the obturator hole and is characterized by its obturator fascia, which thickens in the central part to form the tendinous arch, which provides fixation to the pelvic diaphragm.

Perineal musculature is differentiated by sex.

Diafragma urogenital masculino:

  • Deep, transverse muscle: It has a hole in the urethra.
  • External sphincter of the urethra: Its function is to close the urethra and is responsible for voluntary urine control.
  • Transverse superficial muscle limits the two triangles in which perineal space is divided.
  • External sphincter of the anus: Is responsible for voluntary management of defecation.
  • Ischiocavernosus muscle: Adheres to the ischiopubic bony branches, forms the pillars of the penis, and participates in ejaculation.
  • Bulbospongiosus muscle: Covers the bulb of the penis and the spongy body and contributes to ejaculation.

Diafragma urogenital femenino:

  • Deep transverse muscle: In addition to the urethral orifice, it contains the vaginal orifice.
  • External sphincter of the urethra: This muscle is shorter than in men due to the disposition of the female urethra.
  • Transverse superficial muscle: Like men, this muscle marks the boundary between the triangles in which the perineal space is divided.
  • External sphincter of the anus: It has an identical disposition and the same function as it presents in man.
  • Ischiocavernosus muscle: In the case of women, this muscle is related to the clitoris and allows its erection.
  • Muscle constrictor of the vagina: There is no spongy bulb; it is an erectile body that fills with blood, narrowing the vaginal orifice when contracting.

Innervations of the musculature

motor:

  • The internal pudendal nerve starts from the nerve roots S2 and S4 for the muscles of the urogenital diaphragm.
  • The nerves of the coccygeal loop begin from the nerve roots S4 and S5 for the powers of the pelvic diaphragm.

Sensitive:

  • The internal pudendal nerve starts from the nerve roots S2, S3, and S4, for the clitoris, the vaginal vestibule, the posterior half of the lips, the penis, and the rear aspect scrotum.
  • The primary and minor abdominogenital nerves of the genital branch start from the nerve root L1.
  • The genitofemoral nerve of the genital branch starts from the nerve roots L1 and L2, the mount of Venus, the anterior half of the labia majora, and the anterior half of the scrotum.
  • The posterior femoral cutaneous nerve of the nerve roots L1 and L2, the anal region.
  • The inferior rectal nerve of the nerve roots S2 and S4, for anal skin and external sphincter of the anus.

Clinical relevance

The perineal body is not more than a central annex for the perineal muscles, and its primary functions are to support the pelvic floor.

Childbirth can cause damage to the perineal body, which can lead to possible prolapse of the pelvic viscera, stretching, and incontinence.

This can be treated with an episiotomy, a surgical cut performed on the perineum.

This practice causes damage to the vaginal mucosa but can prevent uncontrolled tearing of the perineal body.

The Bartholin glands are located inside the most superficial perineal pouch of the urogenital triangle.

The function of these glands is mainly to produce a small amount of fluid, which lubricates the vaginal lips during sexual intercourse.

Usually, Bartholin’s glands can not be detected on a physical examination.

However, if this duct is blocked, the glands swell and form cysts saturated with fluids.

These inflamed cysts are usually infected and cause a condition known as bartholinitis.

The most frequent cause of this infection is caused by bacteria such as Staphylococcus spp. and Escherichia coli.

Hemorrhoids are painful, swollen veins in the anal canal or anus.

Internal hemorrhoids occur in the anal canal; external hemorrhoids affect the anus and are easy to see and feel; these can be quite painful and cause bleeding and itching.

Topical medications used to treat hemorrhoids help reduce hemorrhoids, and changes in the patient’s diet can prevent its advent.

In some cases, surgery is recommended, usually when the recurrences of these symptoms are pretty frequent and annoying.