ArticlesAnatomyPelvis and perineumPerineal region

ArticlesAnatomyPelvis and perineumPerineal region

Perineal region

Author: Lorenzo Crumbie, MBBS, BSc • Reviewer: Uruj Zehra, MBBS, MPhil, PhD
Last reviewed: April 08, 2025
Reading time: 16 minutes

The perineal region, or perineum, is the region of the body located directly below the pelvic diaphragm, forming the most inferior part of the pelvis. It is a roughly diamond-shaped area extending from the pubic symphysis anteriorly, the tip of the coccyx posteriorly and between the ischial tuberosities laterally.

The perineal region plays an essential role in providing support to pelvic organs and allowing the passage of structures involved in urination, defecation, reproduction and childbirth.

This article will delve into the structure, contents and neurovascular supply of the perineum, in addition to the anatomical disparities between males and females.

Key facts about the perineal region
Definition	Diamond-shaped region below pelvic diaphragm, which forms the most inferior part of the pelvis and contains the external genitalia and anus.
Boundaries	Anterior: Pubic symphysis Posterior: Tip of coccyx Lateral: Ischial tuberosities Divided into urogenital and anorectal triangles by interischial line.
Urogenital triangle	Anterior part of perineal region, contains external genitalia and openings of urinary and reproductive tracts. Divided into superficial and deep perineal pouches.
Anorectal triangle	Posterior part of perineal region, contains anal canal, ischioanal fossae, external anal sphincter and supporting structures.
Superficial perineal (Colles') fascia	Continuous anteriorly with Scarpa’s fascia of abdomen. Attaches to ischiopubic rami laterally and perineal membrane posteriorly. Lines scrotum (males) or labia (females).
Deep perineal fascia	Encloses superficial perineal muscles (ischiocavernosus, bulbospongiosus, superficial transverse perineal). Attaches to perineal membrane and surrounding structures.
Superficial perineal pouch	Location: Between perineal membrane and deep perineal fascia. Contents: Superficial perineal muscles, corpora cavernosa, corpus spongiosum, pudendal vessels/nerves, bulb of penis (males); bulbs of vestibule and greater vestibular glands (females).
Deep perineal pouch	Location: Between perineal membrane (inferiorly) and pelvic diaphragm (superiorly). Contents: Deep transverse perineal muscles, external urethral sphincter, urethra (and vagina in females), bulbourethral glands (males), pudendal neurovasculature.
Blood supply	Internal pudendal artery, perineal artery, inferior rectal artery.
Innervation	Pudendal nerve, perineal nerve, inferior rectal nerve, dorsal nerve of clitoris/penis.

Contents

Boundaries of the perineal region
Urogenital triangle
Anorectal triangle
1. Structure
2. Structural differences between the male and female
Blood supply
Innervation
Clinical significance
1. Trauma and extravasation of body fluids
2. Episiotomy
Sources
Related articles
Related videos

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Boundaries of the perineal region

The boundaries of the perineal region are defined by the pubic symphysis and the inferior border of the arcuate ligament anteriorly and by the tip of the coccyx posteriorly. The ischiopubic rami and ischial tuberosities border it anterolaterally and the sacrotuberous ligaments posterolaterally.

Externally, the perineal region is covered by skin, which blends with the skin of the thighs and lower abdomen. Superiorly, the perineum is limited by the pelvic diaphragm, formed by the pelvic floor muscles and their overlying fascia.

An imaginary horizontal line, the interischial line, connects the ischial tuberosities and divides the perineum into two triangular regions: the urogenital triangle anteriorly containing the external genitalia and openings of the urinary and reproductive tracts and the anal triangle posteriorly containing the anal canal and its surrounding structures.

Urogenital triangle

The urogenital triangle is the anterior portion of the perineal region bounded posteriorly by the interischial line. The general plan of this region is similar in males and females but a significant amount of sexual dimorphism exists with respect to the contents of the area. In both sexes, the urogenital triangle is divided into superficial and deep perineal spaces (pouches) by the perineal membrane.

The perineal membrane is a sheet of fibrous tissue and has thickened attachments along the borders of the urogenital triangle. It is also referred to as the inferior fascia of urogenital diaphragm. Anteriorly, it attaches to the arcuate ligament of the pubic symphysis, where it forms a thickened band known as the transverse perineal ligament in males and the pubourethral ligament in females. The posterior border of perineal membrane is attached to the perineal body.

Deep to the perineal membrane is the deep perineal pouch, which is also limited deeply by the endopelvic fascia of the pelvic floor. The endopelvic fascia is an umbrella term for the connective tissue that envelops the pelvic organs and attaches them to the lateral walls of the pelvis. The deep perineal pouch is occupied by the puboperinalis and deep transverse perinei muscles.

Superficial to the perineal membrane is the superficial perineal pouch. This space is limited inferiorly by the deep perineal fascia, which is a sheet of fascia that covers the superficial perineal muscles. Its contents include the superficial transverse perineal muscles (superficial transverse perinei, bulbospongiosus and ischiocavernosus) along with the pudendal neurovasculature, corpus spongiosum and corpora cavernosa.

Further superficial is the superficial perineal fascia, also known as Colles' fascia. The region between the membranous layer of superficial perineal fascia and deep perineal fascia is known as the subcutaneous perineal pouch. The superficial perineal fascia is anchored laterally to the ischiopubic rami and posteriorly to the perineal membrane. Anteriorly, this fascia extends to cover the skin of the urogenital triangle. In males, it continues to line the skin of the scrotum, which houses the dartos muscle. In both sexes, Colles' fascia becomes continuous with the membranous layer of the superficial fascia of the anterior abdominal wall, commonly referred to as Scarpa's fascia.

Another important landmark of the urogenital triangle is the perineal body. This ill-defined, fibromuscular mass is located in the middle of the interischial line, between the two triangles. Many muscles have an attachment to the perineal body. It has posterior communications with the external anal sphincter and anterior relations with bulbospongiosus and the deep and superficial transverse perinei. The perineal body also extends superiorly into the rectoprostatic (rectovaginal) septum of the pelvis.

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Muscles of the urogenital triangle

There are several muscles found in the urogenital triangle that are important for reproduction and urinary excretion. Some of these muscles include:

Superficial transverse perinei: as the name suggests, these muscles course transversely across the superficial perineal space with the anus posterior to them. Each has an attachment on the anteromedial surface of the ischial tuberosity and interlinks at the perineal body with the fibers of its counterpart muscle on the other side.

Deep transverse perinei: have several attachments in the deep perineal pouch. As they span the space in a transverse manner (albeit, incompletely), each deep transverse perineal muscle attaches to the ischiopubic rami laterally and similar to the superficial transverse perinei, interlinks at the perineal body with the fibers of its counterpart muscle on the other side. The muscle has an anterior deficiency.

Bulbospongiosus: differs between males and females. In the latter, the muscle is superficial to the bulbs of the vestibule and the associated glands. They subsequently travel lateral to the vagina and insert into the corpora cavernosa of the clitoris along with the body of the glans clitoris itself. However, in the former, the muscle starts as identical halves and fibers decussate in the perineal body and are attached to superficial transverse perinei muscles. The muscle assists with voiding the urethra after micturition and also in expelling semen or vaginal secretions during the ejaculatory process.

Ischiocavernosus: is found in both males and females, although it is significantly larger in males. It is attached medially to the ischial tuberosity and ischial rami. The aponeurotic ending of the muscle merges into the crus of the penis (or clitoris in females). The primary action in males is to aid in stabilizing the erect penis; and in females it assists in promoting clitoral erection.

Learn everything about the muscles of the pelvic floor and perineum with the following study unit!

Female urogenital triangle

The female urogenital triangle contains the mons pubis, labia majora, labia minora, the clitoris and the vaginal and urethral orifices. The perineal body is attached to the vaginal introitus, as well as the posterior commissure of the labia majora. In addition to the other muscles of the deep perineal pouch, females also have the urethrovaginalis muscle that surrounds both the urethral and vaginal orifices.

The urogenital diaphragm is traversed centrally by the urethra and vagina. It is supported anteriorly by the pubourethral ligament, while several structures pass through or lie within this region, including the urethra, vagina, ducts of the greater vestibular (Bartholin’s) glands, labial neurovasculature and the deep dorsal neurovasculature of the clitoris.

Male urogenital triangle

The male urogenital triangle houses the bulb of the penis, the scrotum and serves as a point of attachment for the penis. The perineal body is continuous with the perineal raphe in the scrotal skin. In males, the bulbourethral ducts, urethra, deep dorsal neurovasculature of the penis and the nerves and vessels of the scrotum all pass over the perineal membrane.

If you're ready for a break from reading, test your knowledge with this quiz on the female perineum!

Anorectal triangle

The anorectal triangle is the posterior part of the perineal region and its general composition is the same in both males and females. The triangle is bounded anteriorly by the interischial line and perineal body, while posteriorly its apex is at the tip of the coccyx.

Structure

The anal canal is present in the middle of the anorectal triangle and on each side is ischioanal (ischiorectal) fossa, which occupies most of the anal triangle. In a transverse section through the pelvis (in a lithotomy position), it has a horse shoe appearance, while in a coronal section (through a vertically erect individual) each fossa appears roughly pyramidal.

The ischioanal fossa is limited by and comprised of the following structures:

Medially by the external anal sphincters and the inferomedial part of the sloping levator ani muscle.
Laterally by the obturator internus muscle and its fascia. The two muscles of the walls abut and form the apex at the rostrolateral margin.
Base is formed by skin.
Space between borders is filled with loose adipose tissue.

The fascia of the obturator internus muscle continues towards the superficial surface of the levator ani and covers the deep region of the ischioanal fossa. At that point, it is called the deep fascia of the anal triangle. Its counterpart, the superficial fascia of the anal triangle, is a continuation of the subcutaneous fascia of the perineal skin and the skin of the buttocks and thigh.

The release of end products of digestion from the gastrointestinal tract is regulated by the external anal sphincters. Cranially, fibers of the muscle integrate with the inferior portion of puborectalis. Some fibers cross anteriorly and blend with the superficial transverse perineal muscles, while others attach to the anococcygeal raphe posteriorly. Caudally, the muscle has anteroposterior attachment from the perineal body to the anococcygeal ligament (and by extension, the coccyx).

Structural differences between the male and female

The anorectal triangles in males and females only differ only in size, where the female anal triangle is significantly wider than that of the male. This disparity is a direct result of the structural differences between the male and female pelvis. Not only is the transverse diameter (distance between the ischial tuberosities) of the female pelvis wider, but the plane of the pelvic outlet (the anteroposterior distance between the pubic arch and the tip of the coccyx) is also longer. This sexual dimorphism accommodates the passage of a baby through the pelvic cavity during childbirth.

Learn even more about the female perineum with the following study unit!

Blood supply

The perineal region is supplied with arterial blood by the following blood vessels:

Internal pudendal artery is the chief arterial supplier of the perineum. This branch of the internal iliac artery (along with its corresponding vein and nerve) enters the perineum by travelling through the pudenal (Alcock's) canal, which is located in the lateral wall of the anorectal fossa. It gives the cavernosal and dorsal arteries to the penis in males as well as branches to the vestibular bulb and vagina in females.
Inferior rectal artery is a branch of the internal pudendal artery that supplies the external anal sphincter.
Perineal arteries also arise from the internal pudendal artery. It forms anastomoses with the same vessel from the opposite side as well as with the posterior scrotal (labial) and inferior rectal arteries. They supply the scrotum (labia), perineal body and the transverse perinei muscles.

The venous return is similar to the arterial homolog.

Innervation

The innervation of the pudendal region follows a similar pattern to that of the blood supply. This region is innervated by:

Pudendal nerves: which give branches known as the inferior rectal nerve, dorsal nerve of the clitoris (penis) and perineal nerves.
Perineal nerve: is the largest branch of the pudendal nerve. It gives rise to muscular supply to the transverse perinei, ischiocavernosus and bulbospongiosus, as well as cutaneous innervation to the labia (scrotum).
Inferior rectal nerve: innervates the external anal sphincter, the skin around the anus and the distal anal canal.
Dorsal nerve of the clitoris (penis): provides neuronal stimulation to the corpus cavernosa (sponge-like erectile tissue of the penis).

Now that you've learned everything about the perineal region, put that knowledge to the test with our customizable quiz below!

Clinical significance

Trauma and extravasation of body fluids

Although the subcutaneous perineal pouch is a relatively small area, it acts as a post-trauma reservoir for extravasating body fluids. Consequently, it has the capacity to distend significantly to accommodate fluid leaking from any broken vessel following traumatic insult to the area. Fortunately, the subcutaneous fascia restricts the leaked fluid to the subcutaneous perineal pouch and prevents flow laterally or posteriorly.

Episiotomy

At the end of pregnancy, expectant mothers may encounter some degree of difficulty expelling the foetus from the vaginal canal. Although there are many aetiologies for this issue, the mother to be can be assisted by performing an episiotomy. An episiotomy is a surgically controlled incision made lateral to the gynaecological perineum, in an oblique direction from the posterior vaginal commissure. In addition to making the external vaginal orifice wider, the incision also reduces the risk of tearing the perineum. An uncontrolled tear would result in a more difficult laceration to repair when compared to the surgically created one.

If the episiotomy isn’t indicated, the mother stands the risk of:

Having an uncontrolled laceration through the perineum and possibly the external anal sphincter. If the laceration is severe, there is the possibility that an anovaginal fistula (direct communication between the anus and vaginal canal) could form.
Furthermore, damage to the external anal sphincter can result in faecal incontinence.

Sources

All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.

References:

Drake, Richard L. Gray's Atlas Of Anatomy. 2nd ed. Philadelphia, PA: Churchill Livingstone/Elsevier, 2015. Print.
Sinnatamby, Chummy S and R. J Last. Last's Anatomy. 12th ed. Edinburgh: Churchill Livingstone/Elsevier, 2011. Print.
Standring, Susan, Neil R Borley and Henry Gray. Gray's Anatomy. [Edinburgh]: Churchill Livingstone/Elsevier, 2008. Print.

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