Perineum: MRCOG Part 1 questions and key facts

The perineal body is a fibromuscular structure at the midpoint of the perineum that serves as an attachment site for various muscles, providing support to the pelvic floor.

Muscles such as the external anal sphincter, bulbospongiosus, superficial transverse perineal muscle, and deep transverse perineal muscle attach to the perineal body. These attachments help stabilise and maintain the integrity of the perineal and pelvic regions, playing roles in functions such as continence and sexual function.

The ischiocavernosus muscle, in contrast, is involved in erecting the clitoris and penis by compressing the outflow veins and pushing blood into the erectile tissue. It is positioned laterally, and its primary attachment is to the ischial tuberosity and the crus of the penis or clitoris, not to the perineal body.

The perineum is divided into two main spaces by the perineal membrane: the superficial and deep perineal pouches. These pouches contain various muscles, nerves, vessels, and glands.

Bartholin's glands are paired structures located on either side of the vaginal orifice within the superficial perineal pouch. They are homologous to the bulbourethral glands in males. Their ducts open into the vestibule, and they produce mucus that lubricates the vagina, particularly during sexual arousal.

The deep perineal pouch lies superior to the perineal membrane and contains structures such as the external urethral sphincter and the deep transverse perineal muscles. It does not contain the Bartholin's glands.

The ischioanal fossa is a fat-filled space located lateral to the anal canal, inferior to the pelvic diaphragm, and does not house the Bartholin's glands. The anal triangle is the posterior part of the perineum containing the anal canal, while the urogenital triangle is the anterior part containing the external genitalia. Although Bartholin's glands are in the urogenital triangle, the specific compartment is the superficial perineal pouch.

The perineum is a diamond-shaped region located inferior to the pelvic diaphragm. It's the area between the thighs, extending from the pubic symphysis anteriorly to the coccyx posteriorly. The diamond shape is defined by four key bony landmarks:

• Anteriorly: The pubic symphysis. This is the cartilaginous joint connecting the two pubic bones.

• Posteriorly: The tip of the coccyx. This is the terminal segment of the vertebral column.

• Laterally (on each side): The ischial tuberosities. These are the bony prominences you sit on. They are part of the ischium, one of the three bones that make up the hip bone.

Imagining a line drawn between the two ischial tuberosities divides the perineum into two triangles:

• Urogenital Triangle (Anterior): Contains the external genitalia and the openings of the urethra and vagina (in females).

• Anal Triangle (Posterior): Contains the anus and the external anal sphincter.

The other options list incorrect landmarks. The anterior superior iliac spines, sacral promontory, ischial spines, pubic tubercles, and iliac crests are all parts of the bony pelvis, but they are not the defining points of the diamond-shaped perineum itself.