The perineum is an anatomical region in the pelvis, located between the thighs and representing the most inferior part of the pelvic outlet. It is separated from the pelvic cavity superiorly by the pelvic floor, and contains structures that support the urogenital and gastrointestinal systems, playing an important role in several functions such as micturition, defecation, sexual intercourse, and childbirth. In this article, we shall look at the anatomy of the perineum – its boundaries, contents, and clinical correlations.
In clinical practice, the term ‘perineum’ is often used to describe the area between the external genitalia and the anus. However, anatomically, the perineum is a diamond-shaped structure, with two main ways of describing its boundaries – the anatomical borders and the surface borders.
The anatomical borders of the perineum are as follows:
The perineum can be subdivided into two parts by a theoretical line drawn transversely between the ischial tuberosities, forming the anterior urogenital triangle and the posterior anal triangle. These triangles are associated with different components of the perineum.
The surface boundaries of the perineum can be seen when the lower limbs are abducted, forming a diamond shape, as follows:
The perineum can be subdivided into two parts by a theoretical line drawn transversely between the ischial tuberosities, forming the anterior urogenital triangle and the posterior anal triangle.
The anal triangle is the posterior half of the perineum. It is bounded by the coccyx, sacrotuberous ligaments, and a theoretical line between the ischial tuberosities. The main contents of the anal triangle are:
The anal aperture is located centrally in the triangle with the ischioanal fossae either side. These fossae contain fat and connective tissue, allowing for expansion of the anal canal during defecation. They extend from the skin of the anal region (inferiorly) to the pelvic diaphragm (superiorly). Another important anatomical structure within the anal triangle is the pudendal nerve, which supplies the whole perineum with somatic fibres.
The urogenital triangle is the anterior half of the perineum, bounded by the pubic symphysis, ischiopubic rami, and a theorectical line between the two ischial tuberosities. The triangle is associated with the structures of the urogenital system – the external genitalia and urethra.
Structurally, the urogenital triangle is complex, with a number of fascial layers and pouches. Unlike the anal triangle, the urogenital triangle has an additional layer of strong deep fascia; the perineal membrane. This membrane has pouches on its superior and inferior surfaces. The layers of the urogenital triangle (deep to superficial) are:
The perineum is a complex anatomical structure, playing an important role in both urinary and reproductive functions. A comprehensive understanding of its anatomy, and its associated clinical correlations, is essential for medical professionals in order to diagnose and treat any disorders relating to the perineum.
The perineum is a diamond-shaped structure that is found between the external genitalia and the anus. In clinical practice, its boundaries are described both by its exact bony margins, or “anatomical borders”, and its surface anatomy, or “surface borders”. These borders are as follows: the anterior side is the pubic symphysis, the posterior is the tip of the coccyx, and the lateral sides are the inferior pubic rami, the inferior ischial rami, and the sacrotuberous ligament. The roof is the pelvic floor, and the base is the skin and fascia.
This diamond-shaped perineum can be further subdivided into the urogenital triangle and the anal triangle. The urogenital triangle contains a number of erectile tissues that form the penis and clitoris, as well as three muscles (the ischiocavernosus, bulbospongiosus, and superficial transverse perineal muscles), and the greater vestibular glands (Bartholin’s glands). The anal triangle contains the perineal body, which is an irregular fibromuscular mass that is located at the junction of the urogenital and anal triangles. This structure contains skeletal and smooth muscle, as well as collagenous and elastic fibres.
The perineal body lies just beneath the skin and acts as an attachment for various muscles of the pelvic floor, such as the levator ani, bulbospongiosus muscle, superficial and deep transverse perineal muscles, external anal sphincter, and external urethral sphincter. In females, it provides tear resistance between the vagina and the external anal sphincter, preventing prolapse, while in males it lies between the bulb of penis and the anus. The major neurovascular supply to the perineum is from the pudendal nerve (S2 to S4) and the internal pudendal artery. They, along with the internal pudendal vein, travel through the obturator fascia, in a canal known as Alcock’s canal.
The importance of the perineal body is found in its clinical relevance. It functions to support the pelvic floor, and damage to the perineal body resulting from childbirth can lead to the prolapse of pelvic viscera. To prevent this from occurring, episiotomies (surgical cuts) can be performed in the perineum, although this results in damage to the vaginal mucosa. Another clinical relevance of the perineal body is found in Bartholin’s gland cysts. These glands normally make a small amount of mucus-like fluid, but if the duct becomes blocked, they can swell and become infected, forming Bartholin’s gland cysts. The most common causes of infection are bacteria such as Staphylococcus spp. and Escherichia coli.
The perineum is an important area of the body that provides a great deal of support for the urogenital and gastrointestinal systems. It contains a number of erectile tissues and muscles that aid with functions such as micturition, defecation, sexual intercourse, and childbirth. In the event of damage to the perineum, such as during childbirth, episiotomies can be performed to protect the perineal body and prevent the prolapse of pelvic viscera. Bartholin’s gland cysts also form an important part of the perineum, and the most common cause of infection is from bacteria such as Staphylococcus spp. and Escherichia coli.
The perineum is the region of the body between the lower abdomen and the thighs. It has a diamond-shaped surface boundary when the lower limbs are abducted, and is divided into two triangles; the anterior urogenital triangle and the posterior anal triangle. Each of these triangles has its own distinct contents, which we shall now examine.
The anal triangle is the posterior half of the perineum, bounded by the coccyx, sacrotuberous ligaments, and a theoretical line between the ischial tuberosities. Its main contents are as follows:
The anal aperture is located centrally in the triangle, with the ischioanal fossae located on either side. These fossae house fat and connective tissue, providing space for expansion of the anal canal during defecation. Additionally, they extend from the skin of the anal region to the pelvic diaphragm. The pudendal nerve, which supplies the perineum with somatic fibres, is also present in the anal triangle.
The urogenital triangle is the anterior half of the perineum, bounded by the pubic symphysis, ischiopubic rami, and a theorectical line between the two ischial tuberosities. It is associated with the structures of the urogenital system; the external genitalia and urethra. It is structurally complex, and, in contrast to the anal triangle, has an additional layer of strong deep fascia; the perineal membrane.
The layers of this triangle (deep to superficial) are:
The perineal body is an irregular fibromuscular mass located at the junction of the urogenital and anal triangles; the central point of the perineum. It contains skeletal muscle, smooth muscle and collagenous and elastic fibres, and is located just deep to the skin. Its main role is to act as a point of attachment for muscle fibres from the pelvic floor and the perineum itself, namely the levator ani (part of the pelvic floor), bulbospongiosus muscle, superficial and deep transverse perineal muscles, external anal sphincter muscle, and external urethral sphincter muscle fibres. In women, it acts as a tear-resistant body between the vagina and the external anal sphincter, supporting the posterior part of the vaginal wall against prolapse.
The perineum is an intricate and complex region, lending vital support to many important anatomical structures. A thorough understanding of its contents and boundaries is essential to the proper study, diagnosis and treatment of disorders of the region.
The perineum is a diamond-shaped area located between the pubis symphysis, the ischial tuberosities and coccyx, bounded anteriorly by the pubic arch, laterally by the ischioanal fossae and posteriorly by the tip of the coccyx. It is divided into two parts; the urogenital region (anterior) and the anal region (posterior). The pelvic outlet is the opening bordered by the pubic arch, ischial tuberosities and coccyx, which separates the pelvic cavity from the perineum. The pelvic outlet is further divided into the urogenital triangle in front and the anal triangle at the back.
The urogenital triangle consists of the urogenital diaphragm, while the anal triangle consists of the external and internal anal sphincter muscles. The contents of the perineum are as follows; the greater vestibular glands, the erectile tissue of the clitoris and penis, the perineal body, the neurovascular supply to the perineal region, and the fascia of the perineum.
In the male, the perineum lies between the bulb of penis and the anus. The major neurovascular supply to the perineum is from the pudendal nerve (S2 to S4) and the internal pudendal artery. The pudendal nerve, along with the internal pudendal artery and vein, travel along the inner surface of the ischial tuberosities, through a “canal” formed by a thickening of the obturator fascia (Alcock’s canal). This bundle then courses downwards through each ischioanal fossa, giving branches to both the anal and genital triangle.
The perineal body is a central attachment for perineal muscles, and functions to support the pelvic floor. Childbirth can lead to damage (stretching/tearing) of the perineal body, thus leading to possible prolapse of pelvic viscera. This may be avoided by an episiotomy, a surgical cut in the perineum. This inevitably causes damage to the vaginal mucosa, but prevents uncontrolled tearing of the perineal body.
The Bartholin's glands are located within the superficial perineal pouch of the urogenital triangle. Their role is to make a small amount of mucus-like fluid. Normally, the Bartholin's glands are not detected on physical examination. However, if the duct becomes blocked, then these glands can swell to form fluid-filled cysts. These cysts can become infected and inflamed, a condition known as bartholinitis. The most common cause of infection is from bacteria such as Staphylococcus spp. and Escherichia coli.
Pelvic floor disorders can also be a result of the perineum. In women, the pelvic floor muscles can become weak due to childbirth, leading to pelvic organ prolapse which can be painful and impair bladder and bowel function. In men, pelvic floor disorder can be a result of an enlarged prostate, which can cause urinary incontinence and decreased sexual pleasure. Additionally, pelvic floor disorders can be caused by nerve damage or muscle weakness due to aging or illness, as well as trauma to the perineum.
The perineum plays an important role in the functioning of the body, and can be the site of numerous medical issues. It is important for physicians to have a basic understanding of the anatomy and physiology of the perineum in order to diagnose and treat any issue related to this area.
