Perineum

Perineum (The area between the thighs and buttocks)

LITHOTOMY POSITION

The perineum refers to the diamond-shaped region (IN LITHOTOMY position) roughly extending between the coccyx and pubic symphysis. In anatomical position its an anteroposterior slit.

Boundaries of the perineum

Pubic symphysis (anteriorly) Inferior pubic rami and ischial rami (anterolaterally) Ischial tuberosities (laterally on each side) Sacrotuberous ligaments (posterolaterally) Tip of coccyx (posteriorly)

The two triangles of perineum 

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The diamond shaped perineum is divided into urogenital triangle (anteriorly) and anal triangle (posteriorly) by a line joining the two ischial tuberosities. The membranous layer of the anterior abdominal wall (called Colle’s fascia here) is attached along this line. At the junction of the two triangles there is a central tendon called “perineal body” in the midline.

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Perineal body

Gynecological perineum

How is the gap below the sub pubic angle is closed in life? 

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By urogenital diaphragm and its two fasciae. Urogenital diaphragm is formed by deep transverse perineal muscles and sphincter urethrae. The inferior fascia is called the perineal membrane which stretches across the pubis rami and forms a base for the attachment of roots of genitalia.

Roots of external genitalia 

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1bulb and 2 crura (in both the sexes). These roots have muscles extending into them( 2 ischio cavernosii and one bulbo spongiosus). Roots are attached to the perineal membrane.

Other muscles in the urogenital triangle  Along

with the muscles of the roots, there a pair of superficial and deep transverse perineal muscles(5 muscles meeting in the median plane)

Muscles in the anal triangle  External

anal sphincter (subcutaneous, superficial and deep parts).  Under surface of levator ani.

Perineal body

 The

perineal body may be damaged during parturition. To avoid injury, the opening for the passage of the fetal head may be enlarged by incising the posterior wall of the vagina and the nearby part of the perineum (episiotomy).

Superficial perineal pouch (space)  Scarpa’s

fascia becomes Colle’s fascia in the urogenital triangle and is attached to the posterior border of perineal membrane. The space between these two fasciae is called the superficial pouch.  Contents- roots of the genitalia with their muscles and transverse perineal muscles, pudendal nerve and its branches along with internal pudendal artery.

Extravasation of urine  As

the superficial perineal space contains the penis, any rupture of the spongy urethra ( due to a blow to the perineum by a manhole lid for example), the urine would pass into the scrotum, around the penis and into the anterior abdominal wall. It will to pass into the front of the thigh because of fusion of membranous layer with the fascia lata.

Deep perineal pouch  Present

between the two layers of urogenital diaphragm. Closed on all sides.  Contents: in both sexes the UGD  In males- membranous urethra and BU glands  In females- prox.part of urethra and part of vagina

Ischiorectal(anal) fossa  Wedge

shaped, fat-filled spaces on eother side of the anal canal in the anal triangle.  Provide space for expansion of anal canal.  Sites of peri anal abscess.  In its lateral wall, pudendal canal (Alcock’s canal) is present.

Pudendal nerve divides into inferior rectal nerve (for the anal triangle) And a perineal nerve and dorsal nerve of penis (clitoris) (for the urogenital triangle).