Anatomy of the perineum

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Introduction0:00–0:24

The perineum is a diamond shaped area and a shallow chamber of the pelvis that lies below the pelvic diaphragm. At first glance it may seem like a small and insignificant area but it actually plays a key role in micturition, defecation, intercourse, and delivery by supporting the urinary, gastrointestinal and reproductive organs of the pelvis!Now, let’s start with the outer surface of the perineum, called the perineal region.

Perineal region0:24–1:31

This region is shaped like a diamond that extends posterolaterally from the inferior surface of the pubic symphysis, to the ischial tuberosities laterally, bounded by the inferior pubic and inferior ischial rami anterolaterally.
From the ischial tuberosities, it continues posteromedially to the sacrum and coccyx, bounded by the sacrotuberous ligaments posterolaterally.
This diamond is divided into two triangles by an imaginary transverse line that extends from the two ischial tuberosities.
These triangles are called the urogenital triangle, which lies anteriorly, and the anal triangle, which lies posteriorly.Now, in the middle of the imaginary line that connects the ischiopubic rami lies an irregular mass called the perineal body.
This mass forms the central point of the perineum, and is a meeting point for many muscles, including the superficial transverse perineal muscles, deep transverse perineal muscles, levator ani, bulbopongiosus, external anal sphincter, and external urethral sphincter muscles.Alright, now, deep to the skin of the perineal region, there’s the perineal fascia.

Perineal fascia1:31–1:46

This fascia has two layers; the superficial perineal fascia, or colle’s fascia, and the deep perineal fascia. The superficial perineal fascia also has two layers; a superficial fatty layer and a deep membranous layer.

Superficial perineal fascia1:46–3:34

The superficial fatty layer differs between females and males. In females, the fatty layer forms the substance of the labia majora, which are the larger folds of the vulva, and the mons pubis, which is the rounded mass that lies anterior to the pubic symphysis.
In males, the fatty layer extends into the penis and the scrotum. In the scrotum, it is replaced by a thin layer of smooth muscle, called the dartos muscle.
In both males and females, this fatty layer continues above with the fatty layer of the superficial abdominal fascia in the lower part of the anterior abdominal wall, called Camper fascia.
The superficial fatty layer also continues posteriorly with a fatty mass that surrounds the anal canal, called the ischioanal fat pad.
Next the superficial perineal fascia, also called Colles fascia, has a deep membranous layer which has many attachments to nearby structures.
Posteriorly, it attaches to the posterior margin of the perineal membrane and the perineal body, meaning this layer doesn’t extend into the anal triangle.
Laterally, it attaches to the deep fascia of the upper and medial sides of the thigh, called the fascia lata. The anterior attachment differs between females and males.
In females, the deep membranous layer and the superficial fatty layer extend into the labia majora. In males, it connects with a layer of connective tissue in the penis and the scrotum, called the dartos fascia.
Finally, in both females and males, the deep membranous layer continues above with the membranous layer of the superficial abdominal fascia in the lower part of the anterior abdominal wall, called Scarpa fascia.
Alright, now let’s discuss the deep perineal fascia, also called the investing fascia, which lies beneath deep to the membranous layer of the superficial perineal fascia.

Deep perineal fascia3:34–4:26

This layer surrounds the ischiocavernosus, bulbospongiosus, and superficial transverse perineal muscles. In both males and females, this layer attaches laterally to the ischiopubic rami.This fascia is also continuous with many supportive structures in both females and males.
In females, it continues anteriorly with a ligament that supports the clitoris, called the suspensory ligament of the clitoris.
In males, it continues with a similar ligament that supports the penis, called the suspensory ligament of the penis. Finally the deep perineal fascia continues above with the deep fascia that invests the muscles of the abdominal wall.Okay, now let’s take a deep breath and have a quick quiz!

Quiz4:26–4:40

Alright, can you name this fascia?Now, let’s switch gears and explore the urogenital triangle. The urogenital triangle is covered by a sheet of fascia called the perineal membrane that extends between the ischiopubic rami.

Urogenital triangle4:40–5:31

This membrane fills the urogenital hiatus, which is the gap in the anterior part of the pelvic diaphragm.In both males and females, this membrane is perforated by the urethra.
In females, it is also perforated by the vagina. Finally, the perineal membrane and the ischiopubic rami form a foundation for the male and female erectile bodies, which lie in the superficial part of the urogenital triangle.Within the urogenital triangle are the perineal pouches, which are two spaces or compartments called the superficial and deep perineal pouches separated by the perineal membrane.
Let’s start with the superficial perineal pouch, which lies between the perineal membrane and Colles fascia. The contents of this pouch differ between females and males.

Superficial perineal pouch5:31–7:46

In males, this pouch contains the root of the penis, which has two parts: the bulb and the crura of the penis. The bulb of the penis lies in the midline and the crura of the penis lie on each side of the bulb.
Each of these parts is associated with one of the superficial muscles of the perineum; the bulbospongiosus muscles cover the bulb of the penis, and the ischiocavernosus muscles cover the crura.
The superficial transverse perineal muscles also lie within the superficial perineal pouch and extend from the ischial tuberosities to the perineal body.
Now, in the female urogenital triangle there are multiple erectile structures. First, there’s the clitoris, which also has paired erectile structures called the crura of the clitoris.
Next are the bulbs of the vestibule, which are paired erectile structures that extend posteriorly from the clitoris lateral to the urethra and the vagina.
Also in the superficial perineal pouch there are the greater vestibular glands, which are two pea-sized glands that lie posterolateral to the vaginal orifice.
Next are the superficial perineal muscles, which are analogous to those in the male perineum. The bulbospongiosus muscles cover the bulbs of the vestibule and vestibular glands.
Then ischiocavernosus muscles cover the crura of the clitoris, and finally the superficial transverse perineal muscles. The last structures in this pouch are the branches from the internal pudendal artery and pudendal nerve.
Both the nerve and the artery give off an inferior rectal branch.The internal pudendal artery continues further and gives off a perineal branch which supplies the bulb of the penis in males or vestibule in females.
The artery ends as the posterior scrotal artery or posterior labial artery. Like the artery, the internal pudendal nerve also gives off a perineal branch which bifurcates into a deep perineal branch and superficial perineal branch, this branch terminates as the posterior scrotal nerve or posterior labial nerve.
Alright, now let’s switch gears and discuss the deep perineal pouch, which lies between the pelvic diaphragm, and the perineal membrane.

Deep perineal pouch7:46–9:36

The pouch is also bound laterally by the membrane that covers the obturator internus muscle, called the obturator fascia.
Now, let’s take a closer look at the contents of the deep perineal pouch. In males and females this pouch contains the anterior extensions of the ischioanal fat pads, and the urethra, which passes through the midline of the pouch.
For males, it is the intermediate or membranous urethra that is within the deep perineal pouch. In both males and females, this part of the urethra is surrounded by the external urethral sphincter.
In the female deep perineal pouch, there are two other smaller muscles - that are actually part of the external urethral sphincter complex- called the compressor urethrae, and the urethrovaginal sphincter.
In males, there are the deep transverse perineal muscles. Traditionally, it has been described that females have a sheet-like, deep transverse perineal muscle.
However the current understanding is that this is not the case. Instead there is a mass of smooth muscle at the posterior edge of the perineal membrane.
In males, the deep perineal pouch also contains the bulbourethral glands, which are a pair of pea-shaped glands that lie below the prostate gland.
Finally lets take a look at the neurovasculature within the deep perineal pouch. This pouch contains the internal pudendal artery, which bifurcates into the deep artery of the penis or clitoris and the dorsal artery of the penis or the dorsal artery of the clitoris.
The pudendal nerve also continues in this pouch and ends as the dorsal nerve of the penis or dorsal nerve of the clitoris.
The deep perineal nerve, a branch from the perineal nerve, supplies the muscles within the superficial and deep perineal pouches.

Quiz9:36–9:49

Okay, now let’s take a deep breath and have a quick quiz! Can you name these pouches?Now, let’s switch gears and discuss the anal triangle, which contains the anal canal and anus, as well as a wedge-shaped space on each side of the anal canal, called the ischioanal fossa.

Anal triangle9:49–10:46

This fossa is filled with loose connective tissue and fat tissue. The ischioanal fossa is bounded medially by the external anal sphincter and the levator ani muscles, posteriorly by the gluteus maximus muscle and sacrotuberous ligament, anteriorly by the pubic bones and laterally by the ischium and the lower part of the obturator internus muscle.
Speaking of the obturator internus muscle, it is covered by a membrane called the obturator fascia. This membrane forms a horizontal passageway called the pudendal or Alcock canal.
This canal contains the pudendal nerve and the internal pudendal blood vessels, which enter the Alcock canal at the lesser sciatic foramen alongside the nerve to obturator internus.
We’ve discussed the vessels that supply the perineum in different pieces, but let’s put it all together now. Let’s start with the internal pudendal blood vessels, which supply and drain blood to and from many structures in the perineum.

Arterial supply10:46–13:50

In the Alocock canal, the internal pudendal artery gives off the inferior rectal artery. The inferior rectal artery passes medially to supply the external anal sphincter and the skin that surrounds the anus, called the perianal skin.
Then, the internal pudendal artery gives off the perineal artery, which goes on to give off two branches, called the artery of the bulb of the penis or the artery of the vestibule and the posterior scrotal or posterior labial branches.
The artery of the bulb of the penis or vestibule supplies the bulb of the penis and the bulbourethral glands in males, and the bulb of the vestibule and the greater vestibular glands in females.
The posterior scrotal branches or labial branches supply the skin of the scrotum or the skin of the labia majora. Finally, the internal pudendal artery enters the deep perineal pouch, to give off its terminal branches, which are the deep artery of the penis in males and the deep artery of the clitoris in females.The deep artery of the penis or clitoris supplies most of the erectile tissues in the penis and the clitoris.
The next terminal branches are the dorsal artery of the penis and the dorsal artery of the clitoris. The dorsal artery of the penis or the clitoris runs through the deep perineal pouch and supplies the dorsal surfaces of the penis and the dorsal surfaces of the clitoris.Now let’s follow the course of the pudendal nerve, which has a similar course and branches as the internal pudendal artery.
In the canal, the pudendal nerve gives off the inferior rectal nerve. At the end of the canal, the pudendal nerve bifurcates into the dorsal nerve of the penis or the clitoris and the perineal nerve.
Lets start with the inferior rectal nerve, which runs with the inferior rectal artery to supply the external anal sphincter and the perianal skin.
Next, the perineal nerve, which gives off two branches - the superficial perineal nerve and the deep perineal nerve. The superficial perineal nerve gives off the posterior scrotal nerves in males or posterior labial nerves in females.
Both lie in the superficial perineal pouch. These nerves run in the superficial fascia of the posterior scrotum or labia majora to supply the skin of the scrotum or the skin of the labia minora and majora.
Next is the deep perineal nerve, which supplies muscles of the deep and superficial perineal pouches, the skin of the vestibule of the vagina, and the mucosa lining the lower part of the vagina.
Finally, the dorsal nerves to the penis or the clitoris are the main sensory nerves that supply the penis and the clitoris.
These nerves run with the dorsal artery, reaching the dorsal surfaces of the penis and the clitoris. Here, the nerves run lateral to the arteries, reaching the tip of the penis or the clitoris.
Alright, as a quick recap, the perineum is a shallow chamber of the pelvis that lies inferior to the pelvic diaphragm. The perineum is divided into an anterior urogenital triangle and a posterior anal triangle, with the perineal body forming the center of the perineum.

Innervation13:50–15:40

The urogenital triangle has two compartments, called the superficial and deep perineal pouches. The superficial perineal pouch lies between the perineal membrane and the perineal fascia.
The pouch contains the erectile bodies, as well as their associated muscles, the greater vestibular glands in females, and the superficial transverse perineal muscles.
The neurovascular structures in the superficial perineal pouch are the inferior rectal and the perineal artery and nerve.
The perineal artery and nerve continue as the posterior labial or scrotal artery and nerve. The deep perineal pouch lies between the pelvic diaphragm and the perineal membrane.
It contains the urethra and external urethral sphincter, as well as the deep transverse perineal muscles and bulbourethral glands in males, and the compressor urethrae, urethrovaginal sphincter and smooth muscle in place of the deep transverse perineal muscle in females.
The neurovascular structures in the deep perineal pouch are the internal pudendal artery, which bifurcates to give off the deep artery of the penis or clitoris and the dorsal artery of the penis or clitoris, the pudendal nerve which ends as the dorsal nerve of the penis or clitoris, and the deep perineal nerve.
Finally is the ischioanal fossa, which lies on each side of the anal canal. On the lateral wall of this fossa lies the Alcock canal, which contains the internal pudendal blood vessels and the