Vulva or Pudendum Embryology, Anatomy, and Histology

Pelvic diaphragm: Levator ani and ischiococcygeus (also called coccygeus) form the pelvic diaphragm and delineate the lower limit of the true pelvis.
- Perineum
  
  (a)
  
  Limits
  
  The deep limit: the inferior surface of the pelvic diaphragm
  
  The superficial limit: the skin which is continuous with that over the medial aspect of the thighs and the lower abdominal wall.
  
  (b)
  
  Comprises
  
  Anal triangle
  
  Urogenital triangle
Urogenital triangle comprises from deep to the superficial:
- Deep perineal space (between deeply the endopelvic fascia of the pelvic floor and superficially the perineal membrane)
- Superficial perineal space (between deeply the perineal membrane and superficially the superficial perineal fascia)
- Vulva or pudendum or external female genitalia compartment (between the superficial fascia and the skin)

Anatomical definition of vulva or pudendum or external female genitalia comprises the following anatomical structures:

Labial formations: Mons pubis, pubis, labia major, labia minora
Erectile organs (clitoris and bulbs of the vestibule)
Glands and their ducts (Bartholin’s and Skene’s glands)
Vestibule containing vaginal orifice (introitus), hymen vaginae
External urethral orifice also called external urethral meatus.

Although most of these anatomical structures belong to the most superficial anatomical compartment of the anterior urogenital triangle (female external genitalia compartment), in fact some of them are located or arise in the superficial perineal space (Table 34.1) (Figs. 34.1 and 34.2)

Table 34.1

Components of the vulva

Anatomical Compartment
Anatomical structures	Vulva	Superficial perineal space
1. Labial formations
Mons pubis	Mons pubis
Labia majora	Labia majora
Labia minora	Labia minora
2. Erectile organs
Clitoris
Corpora cavernosa		Corpora cavernosa
Corpus clitoridis	Corpus clitoridis (1/2 anterior)	Corpus clitoridis (1/2 posterior)
Glans	Glans
Bulbs of the vestibule	Bulbs of the vestibule (anterior part: joins to the posterior part of corpus clitoridis)	Bulbs of the vestibule (posterior and middle part)
3. Glands
Greater vestibular glands	Greater vestibular glands (anterior part)	Greater vestibular glands (posterior and middlepart)
Ducts	Ducts
Skene’s glands	Skene’s glands	Skene’s glands
Skene’s ducts	Skene’s ducts	Skene’s ducts
4. Vestibule (between labia minora)
Urethra	Urethral meatus (in vestibule)	Urethra (part of perineal portion)
Vagina	Vaginal orifice (in vestibule)	Vagina (part of perineal portion)
	Hymen

Vulva or pudendum or female external genitalia compartment is limited by:
- Deeply
  
  The superficial perineal fascia also called Colles’ fascia which is attached to:
  
  Posteriorly, the fascia over the superficial transverse perinei and the posterior limit of the perineal membrane.
  
  Laterally, the margins of the ischiopubic rami and the ischial tuberosities; from here it runs more superficially to the skin of the urogenital triangle, lining the external genitalia, where it ends in the labia majora.
- Superficially
- The skin.
Superficial perineal space
(a)
Is limited by

Deeply

The perineal membrane, which is triangular and is attached

Laterally to the periosteum of the ischiopubic rami

The posterior border is fused with the deep part of the perineal body and is continuous with the fascia over the deep transverse perinei. The upper sheet is continuous posteriorly with the lower part of the rectovaginal septum

Anteriorly at the apex fascia over transverse perinei and the perineal membrane join to form very tight aponeurotic fibres, the transverse ligament of Henlé also called the pubourethral ligament. Its apex is attached to the arcuate ligament of the pubis

Superficially

The superficial perineal fascia also called Colles’ fascia.
(b)
It contains

Superficial transverse perinei (mainly posteriorly)

Bulbospongiosus (medially)

Attaches to the perineal body

On each side is separate

Covers the superficial part of the vestibular bulbs and greater vestibular glands; the vestibular bulbs run anteriorly on each side of the vagina to attach to the corpora cavernosa clitoridis

Ischiocavernosus (laterally)

Attaches on the ischiopubic ramus on both sides of the corpus clitoridis

Covers the corpora cavernosa of the clitoridis, ends in an aponeurosis attached to the sides and under surface of the of the crus; anteriorly corpora cavernosa of the clitoridis join to form the corpus clitoridis (hidden part)

34.2 Embryology [1] (See Fig. 1.4)

34.2.1 Common Development in Female and Male

Up to the seventh week, the external genitalia are similar in both sexes. Distinguishing sexual characteristics begin to appear during the ninth week, but the external genitalia are not fully differentiated until the 12th week.

In the fourth week, proliferating mesenchyme produces a genital tubercle at the cranial end of the cloacal membrane.

Labioscrotal swellings and urogenital folds soon develop on each side of the cloacal membrane. The genital tubercle elongates to form a primordial phallus.

When the urorectal septum fuses with the cloacal membrane at the end of the sixth week, it divides the cloacal membrane in a dorsal anal membrane and a ventral urogenital membrane.

The urogenital membrane lies in the floor of a median cleft, the urethral groove, which is bound by the urogenital folds. The anal and urogenital membranes rupture a week later, forming the anus and urogenital orifices. The urethra and the vagina open in a common cavity, the vestibule.

34.2.2 Development of Male External Genitalia

Masculinization of the indifferent external genitalia is induced by testosterone produced by the interstitial cells of the fetal testes.

As the phallus enlarges and elongates to become the penis, the urethral folds form the lateral walls of the urethral groove on the ventral surface of the penis.