ArticlesAnatomyPelvis and perineumPerineal region

ArticlesAnatomyPelvis and perineumPerineal region

Perineal region

Author: Lorenzo Crumbie, MBBS, BSc • Reviewer: Uruj Zehra, MBBS, MPhil, PhD
Last reviewed: May 08, 2025
Reading time: 13 minutes

The perineal region, or perineum, refers to the anatomical region located between the thighs, extending from the pubic symphysis anteriorly to the tip of the coccyx posteriorly. It represents the most inferior portion of the pelvis, situated directly below the pelvic diaphragm.

This region encompasses the external genitalia and the anal opening, and plays a vital role in several bodily functions, including urination, defecation, sexual activity and childbirth. Structurally, the perineum supports the pelvic organs and provides passage for the urogenital and gastrointestinal tracts.

This article will delve into the anatomy, contents and neurovascular supply of the perineum, as well as the clinical relevance of the perineal region, with a focus on its differences between males and females.

Key facts about the perineal region
Definition	Diamond-shaped region inferior to the pelvic diaphragm, housing the external genitalia and anus
Boundaries	Anterior: Pubic symphysis Posterior: Tip of coccyx Lateral: Ischial tuberosities Anterolateral: Ischiopubic rami Posterolateral: Sacrotuberous ligaments
Subdivisions	Divided by the interischial line into: Urogenital region (anterior) Anal region (posterior)
Urogenital region	Contains external genitalia and urethral/vaginal openings. Subdivided into: Superficial perineal space: Erectile tissue, superficial muscles, pudendal neurovasculature Deep perineal space: Deep muscles, external urethral sphincter, urethra (and vagina in females), bulbourethral glands (males)
Anorectal triangle	Contains anal canal, ischioanal fossae, external anal sphincter, and supporting fat and fascia
Fasciae	Membranous layer of perineal subcutaneous tissue (Colles’ fascia) (superficial): Continuation of membranous layer of abdominal subcutaneous tissue (Scarpa’s fascia); lines labia/scrotum Perineal fascia: Covers superficial perineal muscles Perineal membrane: Separates superficial and deep spaces
Blood supply	Internal pudendal artery, perineal artery, inferior rectal artery
Innervation	Pudendal nerve (S2-S4), perineal nerve, inferior rectal nerve, dorsal nerve of clitoris/penis

Contents

Boundaries of the perineal region
Urogenital triangle
Anorectal triangle
Blood supply
Innervation
Clinical notes
Sources
Related articles
Related videos

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Boundaries of the perineal region

The perineum is bordered:

Anteriorly by the pubic symphysis and arcuate ligament,
Posteriorly by the coccyx,
Anterolaterally by the ischiopubic rami and ischial tuberosities,
Posterolaterally by the sacrotuberous ligaments.

The overlying skin blends seamlessly with adjacent areas of the thighs and lower abdomen, while superiorly the region is limited by the pelvic diaphragm, which consists of pelvic floor muscles and associated fascia.

An imaginary horizontal line, the interischial line, connects the ischial tuberosities and divides the perineum into two triangular regions:

The urogenital region (anterior): Contains the external genitalia and urinary/reproductive tract openings.
The anal triangle (posterior): Houses the anal canal and associated structures.

Urogenital triangle

The urogenital region (or triangle) forms the anterior portion of the perineal region. It is bounded posteriorly by the interischial line, and its borders include the pubic symphysis anteriorly and the ischiopubic rami laterally. This region contains the external genitalia and the openings of the urinary and reproductive tracts. Although the overall structure is similar in males and females, there are key sex-specific differences in its contents.

The perineal membrane is a dense fibrous sheet that provides structural support and serves as a point of muscular and fascial attachment. It spans the urogenital triangle horizontally and marks the inferior boundary of the urogenital diaphragm. Anteriorly, it attaches to the arcuate ligament of the pubic symphysis and contributes to the formation of the transverse perineal ligament (in males) or pubourethral ligament (in females). Posteriorly, it anchors to the perineal body, a central fibromuscular mass.

An important feature of the urogenital triangle is its division into two horizontal compartments by the perineal membrane:

The superficial perineal space, located below the perineal membrane
The deep perineal space, located above the perineal membrane and beneath the pelvic diaphragm

Deep perineal space

Located between the perineal membrane (inferiorly) and the pelvic diaphragm (superiorly), the deep perineal space contains:

Deep transverse perineal muscles
External urethral sphincter
Urethra (and vagina in females)
Bulbourethral glands (in males)
Branches of the pudendal nerve and internal pudendal vessels

In females, the urethrovaginalis muscle, which encircles both the urethra and vagina, is also found in this space.

Superficial perineal space

The superficial perineal space lies between the perineal membrane (superiorly) and the perineal fascia (inferiorly). It contains:

Superficial transverse perineal muscles
Bulbospongiosus and ischiocavernosus muscles
Erectile tissue (corpora cavernosa and corpus spongiosum in males; bulbs of the vestibule and clitoral structures in females)
Greater vestibular glands (of Bartholin) in females
Pudendal nerve branches and internal pudendal vessels

Fascial layers

The region is enclosed by important fascial layers:

Perineal fascia (investing fascia): Covers the superficial perineal muscles.
Membranous layer of perineal subcutaneous tissue (Colles’ fascia): A continuation of membranous layer of abdominal subcutaneous tissue (Scarpa’s fascia) of the anterior abdominal wall. It fuses laterally with the ischiopubic rami and posteriorly with the perineal membrane. It helps form the subcutaneous perineal space, especially relevant in trauma.

In males, Colles’ fascia continues into the scrotum, where it encloses the dartos muscle of scrotum. In both sexes, it contributes to the overall compartmentalization and limits fluid spread in cases of injury.

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Perineal body

Centrally located along the posterior margin of the urogenital region, the perineal body serves as a critical point of muscular convergence and reinforcement. Several muscles attach here, including:

Bulbospongiosus
Superficial and deep transverse perineal muscles
External anal sphincter
Fibers of the levator ani

It also extends superiorly into the rectovaginal or rectoprostatic septum, forming part of the pelvic floor support system.

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: Transverse fibers that anchor to the perineal body.
Deep transverse perinei: Span the deep perineal pouch with a transverse but incomplete course.
Bulbospongiosus: Aids ejaculation or vaginal secretion; supports erectile function.
Ischiocavernosus: Stabilizes the penis or assists in clitoral erection.

Sex-specific features:

In females, the triangle includes the mons pubis, labia, clitoris, and orifices of the urethra and vagina.
In males, it contains the bulb and root of the penis and scrotum.

Check out this study unit to learn about all of the muscles of the pelvic floor and perineum.

Anorectal triangle

The anorectal triangle is the posterior subdivision of the perineal region. It lies behind the interischial line and is bordered:

Anteriorly by the interischial line and the perineal body
Posteriorly by the tip of the coccyx
Laterally by the sacrotuberous ligaments
Inferiorly by the skin of the perineum

At the center of this triangle lies the anal canal, flanked on either side by the ischioanal (ischiorectal) fossae, which are fat-filled spaces that support the anal canal and allow for its expansion during defecation.

Ischioanal fossa

Each ischioanal fossa is shaped roughly like a pyramid (in coronal view) or horseshoe (in transverse view). These fossae extend anteriorly into the urogenital triangle, forming anterior recesses.

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 lining these spaces includes:

Deep fascia of the anal triangle (overlying the levator ani)
Superficial fascia of the anal triangle, continuous with the subcutaneous fascia of the perineum and lower gluteal region

External anal sphincter

The external anal sphincter is a circular skeletal muscle that encircles the anal canal and provides voluntary control over defecation. It has cranial connections with the puborectalis muscle, posterior attachments to the anococcygeal ligament, and anterior links to the perineal body. Some fibers also blend with the superficial transverse perineal muscles, enhancing structural cohesion.

Sexual dimorphism

Although the basic architecture of the anorectal triangle is similar in both sexes, the female triangle is generally wider, owing to the broader pelvic outlet. This difference accommodates childbirth and is due to a greater distance between the ischial tuberosities and an expanded anteroposterior pelvic diameter.

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

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

Blood supply

The internal pudendal artery, a branch of the internal iliac artery, is the primary vascular supplier of the perineum. It enters the region via the pudendal (Alcock’s) canal, located along the lateral wall of the ischioanal fossa, accompanied by the pudendal nerve and internal pudendal vein.

Main arterial branches include:

Perineal artery: Supplies the superficial perineal structures, including the skin, scrotum/labia, and muscles of the urogenital triangle
Inferior rectal artery: Supplies the external anal sphincter, anal canal, and perianal skin.
Terminal branches:
- Dorsal artery of the penis/clitoris
- Cavernosal artery (important in erectile function)
- Arteries to the bulb and vestibule

Venous return mirrors the arterial supply and drains into the internal pudendal vein, which in turn drains into the internal iliac vein. The perineal venous plexus communicates with pelvic venous networks and may play a role in temperature regulation of the testes in males.

Innervation

The perineum receives motor and sensory innervation primarily from the pudendal nerve (S2–S4). This nerve travels through the greater sciatic foramen, loops around the ischial spine, and enters the perineum via the lesser sciatic foramen, traversing Alcock’s canal alongside the internal pudendal vessels.

Major branches of the pudendal nerve:

Inferior rectal nerve:
- Innervates the external anal sphincter
- Supplies sensory fibers to the anal canal and perianal skin
Perineal nerve:
- Largest branch
- Provides motor innervation to bulbospongiosus, ischiocavernosus, and transverse perineal muscles
- Supplies sensory innervation to the posterior scrotum or labia
Dorsal nerve of the penis/clitoris:
- Terminal branch
- Provides sensory innervation to the glans, corpora cavernosa, and adjacent skin
- Plays a key role in sexual arousal and reflexes

Together, these nerves ensure voluntary control over urination, defecation, and sexual function, as well as somatic sensation in the perineal region.

Clinical notes

The perineum is clinically significant due to its involvement in common obstetric procedures, susceptibility to trauma, and its role in pelvic floor integrity. Key clinical considerations include:

Trauma and fluid extravasation

The subcutaneous perineal space, the space between Colles’ fascia and the perineal fascia, is an important area in trauma. Although small under normal conditions, this space can expand significantly to accommodate fluids such as blood or urine following injury.

For example, in anterior urethral injuries (commonly due to straddle trauma in males), urine may extravasate into the superficial perineal pouch. The attachments of Colles’ fascia restrict the spread of fluid laterally and posteriorly but allow it to ascend into the anterior abdominal wall, following Scarpa’s fascia.

This fascial continuity explains the characteristic pattern of swelling and bruising seen in such injuries—extending to the scrotum, penis, and lower abdominal wall in males.

Episiotomy

An episiotomy is a controlled surgical incision made in the posterior wall of the vaginal orifice, extending through the perineal body. It is commonly performed during the second stage of labor to:

Enlarge the vaginal opening
Facilitate childbirth
Reduce the risk of spontaneous tearing

The incision is usually made in a mediolateral direction to minimize damage to the external anal sphincter and other pelvic floor structures.

If an episiotomy is not performed when indicated, spontaneous perineal tears may occur, which can be:

More difficult to repair
Involve the anal sphincter complex, potentially leading to complications such as: Fecal incontinence and anovaginal fistula formation (a pathological communication between the rectum and vagina).

Importance of the perineal body

The perineal body acts as a central anchor point for several pelvic floor muscles. Damage to this structure, whether through childbirth, trauma, or surgical injury, can compromise pelvic floor stability and contribute to:

Pelvic organ prolapse
Urinary or fecal incontinence
Sexual dysfunction

Proper support and restoration of the perineal body during pelvic floor repairs is essential for long-term continence and organ support.

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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