Perineal body: the central fibromuscular anchor of the perineum
The perineal body is a knot of muscle and fibrous tissue (a fibromuscular mass) at the centre of the perineum, the diamond-shaped region that contains the anus and external genitalia.
Remember
Many muscles meet at the perineal body, so a tear through it weakens their combined support rather than that of a single muscle.
Memory aid
the hub of a wheel, with muscular spokes meeting in the middle
Picture the perineal body as the hub of a wheel, with the muscles that attach to it as the spokes meeting in the middle.
The perineal body sits where the urogenital triangle, the front half of the perineum that relates to the urinary and genital organs, meets the anal triangle, the back half. In women it lies between the vagina and the anus, and in men between the bulb of the penis and the anus. It is made of muscle (skeletal and smooth) and fibrous tissue (collagen and elastic fibres), hence fibromuscular.
Many muscles converge on it, including bulbospongiosus (one of the superficial perineal muscles), the superficial and deep transverse perineal muscles (thin muscles that run across the perineum), the external anal sphincter (the voluntary muscle ring around the anus) and part of levator ani (the main sheet of pelvic floor muscle).
With these muscles tied into one central point, the perineal body helps the pelvic floor to resist a downward push when the pressure inside the abdominal cavity goes up.
In women, between the vagina and the external anal sphincter, it acts as a tear-resistant body, and it supports the back wall of the vagina against prolapse (organs sagging into the vagina).
Childbirth can stretch or tear the perineal body. A deep midline tear can separate the muscles from their shared anchor, so their combined support is weakened and prolapse can follow.
Key facts
- Position
- the centre of the perineum, where the urogenital and anal triangles meet; in women it lies between the vagina and the anus, and in men between the bulb of the penis and the anus
- Make-up
- skeletal muscle, smooth muscle, collagen and elastic fibres
- Attachments
- part of levator ani, bulbospongiosus, the superficial and deep transverse perineal muscles, the external anal sphincter and fibres of the external urethral sphincter
- Role in women
- a tear-resistant body that supports the back wall of the vagina against prolapse
- Childbirth
- stretching or tearing of the perineal body can weaken pelvic support and lead to prolapse
Exam traps
- Coccygeus, a small triangular pelvic floor muscle behind levator ani, supports the pelvic organs, but it sits at the back of the pelvis, so it is not among the usual attachments of the perineal body.
- Ischiocavernosus, a superficial perineal muscle at the root of the clitoris or penis, lies close to bulbospongiosus, yet it is not among the muscles that converge on the perineal body.
- The pudendal nerve supplies the pelvic floor and perineum, but it is a nerve, not a structural anchor for the muscles and skin it supplies.
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