Perineum

The perineum is a diamond-shaped region below the pelvic diaphragm and is divided by an imaginary line drawn between the ischial tuberosities into anteriorly the urogenital triangle and posteriorly the anal triangle.

Gross anatomy

The perineum is bounded by the pubis anteriorly, the ischial tuberosities anterolaterally, the sacrotuberous ligaments posterolaterally and the coccyx posteriorly.

The urogenital triangle is the anterior part of the perineum and it contains the penis and scrotum in males and mons pubis, labia majora and minora, clitoris and vaginal and urethral orifices in females. A sheet of fascia covers the urogenital diaphragm inferiorly, the perineal membrane, which divides the urogenital triangle into the deep perineal pouch superior (deep) to the membrane and the superficial perineal pouch inferior (superficial) to the membrane. The perineal membrane is less conspicuous in females.

The anal triangle contains the anus and its sphincters and also the ischioanal fossa on either side in both males and females.

The central tendon of the perineum is the midpoint of the joining line between the ischial tuberosities and is called the perineal body. The perineal body lies behind the vagina in females and supports the vagina against prolapse. The anal sphincters, bulbospongiosus muscle, superficial and deep transverse perineal muscles and levator ani muscles form a close anatomic relationship with the perineal body in the midline.

Arterial supply

The internal pudendal artery is a branch of the internal iliac artery and is the main supplier of the perineum.

Innervation

The pudendal nerve (S2 to S4), and its branches, are the nerves of the perineum and pelvic floor.

Radiographic features

Imaging is required to assess pelvic floor laxity in women with urinary and bowel continence issues.

CT

Provides limited visualization of the pelvic muscles.

MRI

Muscles of the pelvic floor can be imaged with MRI and pelvic floor movements can be assessed with dynamic MRI.

MRI is the modality of choice in assessing the complex perineal lesions and their relations to the adjacent structures. It provides guidance for surgical planning due to its greater sensitivity and specificity than the other non-invasive imaging techniques.