Chapter 3: Perineum

INTRODUCTION

The perineum is a diamond-shaped space that lies below the pelvic floor (Fig. 3-1). Its boundaries are as follows:

1. Superiorly: the pelvic floor made up of the levator ani muscles and the coccygei

2. Laterally: the bones and ligaments that make up the pelvic outlet; from front to back, these are the subpubic angle, ischiopubic rami, ischial tuberosities, sacrotuberous ligaments, and coccyx

3. Inferiorly: the skin and fascia

This area is divided into two triangles: anteriorly, the urogenital triangle; posteriorly, the anal triangle. These are separated by a transverse band composed of the transverse perineal muscles and the base of the urogenital diaphragm.

UROGENITAL TRIANGLE

The urogenital triangle is bounded:

1. Anteriorly: by the subpubic angle

2. Laterally: by the ischiopubic rami and the ischial tuberosities

3. Posteriorly: by the transverse perineal muscles and the base of the urogenital diaphragm

The urogenital triangle contains:

1. Opening of the vagina

2. Terminal part of the urethra

3. Crura of the clitoris with the ischiocavernosus muscles

4. Vestibular bulbs (erectile tissue) covered by the bulbocavernosus muscles

5. Bartholin's glands and their ducts

6. Urogenital diaphragm

7. Muscles that constitute the central point of the perineum (perineal body)

8. Perineal pouches, superficial and deep

9. Blood vessels, nerves, and lymphatics

Urogenital Diaphragm

The urogenital diaphragm (triangular ligament) lies in the anterior triangle of the perineum. It is composed of muscle tissue covered by fascia.

1. The two muscles are the deep transverse perineal and the sphincter of the membranous urethra

2. The superior layer of fascia is thin and weak

3. The inferior fascial layer is a strong fibrous membrane. It extends from a short distance beneath the arcuate pubic ligament to the ischial tuberosities. The fascial layers fuse superiorly and form the transverse perineal ligament. Inferiorly, they join in the central point of the perineum

The deep dorsal vein of the clitoris lies in a small space between the apex of the urogenital diaphragm and the arcuate pubic ligament. Through the diaphragm pass the urethra, the vagina, blood vessels, lymphatics, and nerves.

Superficial Perineal Pouch

The superficial perineal pouch is a space that lies between the inferior layer of the urogenital diaphragm and Colles fascia.

Superficial Transverse Perineal Muscles

The superficial transverse perineal muscles are the superficial parts of the deep muscles and have the same origin and insertion. These are outside the urogenital diaphragm. Sometimes they are entirely lacking.

Ischiocavernosus Muscles

The ischiocavernosus muscles cover the clitoral crura. The origin of each is the inferior ramus of the pubis, and they insert at the lateral aspect of the crus. These ...