Anatomy of the perineum

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. 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. 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. 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.