Anatomy Vulva

The vulva represents the external female genitalia, whose functions include sexual arousal, entrance for coitus, exit for the newborn, and outlet for the urinary tract. It lies within the anatomical compartment of the perineum, defined superiorly by the pelvic diaphragm, inferiorly by the skin between the buttocks and the thighs, and transversely by a diamond-shaped osteoligamentous frame, whose points are the pubis, ischial tuberosities, and coccyx. The perineum is divided by a transverse line connecting the ischial tuberosities into the anterior (urogenital) and posterior (anal) triangles. The vulva lies within the anterior triangle. It is composed of the mons pubis, labia majora, labia minora, vaginal vestibule, clitoris, urethral meatus, bulbs, greater vestibular (Bartholin's) and paraurethral (Skene's) glands, hymen, and clinical perineum. The clinical perineum is different from the anatomical perineum, and is defined as the skin between the vulva and the anus.

Surface Anatomy

The surface limits of the vulva are anteriorly, the horizontal limit of the pubic hair of the mons pubis, laterally, the genitocrural folds, posteriorly, the anus, and centrally, the hymenal ring of the vaginal introitus (1).

Mons Pubis. The mons pubis is a mound of skin-covered subcutaneous fatty tissue overlying the pubic bone. It is continuous with the subcutis of the anterior abdominal wall superiorly and the labia majora posteriorly. The mons becomes covered with coarse hair and the amount of fat increases at puberty. These gradually decrease after menopause.

Labia Majora. The right and left labia majora are symmetrical, large, lateral folds of subcutaneous fat covered by skin that may be pigmented in light-skinned women. They are continuous with the mons pubis anteriorly and ischiorectal fat posteriorly. They fuse anteriorly at the anterior commissure at the base of the mons pubis and posteriorly at the posterior commissure (fourchette), 3 to 4 cm in front of the anus.

They flatten posteriorly before fusing. The lateral (outer) surfaces are apposed to the medial aspects of the thighs and the medial surfaces are apposed to the lateral surfaces of the labia minora. Like the mons, the lateral surfaces become covered by coarse hair to a varying degree and the amount of fat increases at puberty. The medial (inner) surfaces are covered by hairless, moist skin. The medial surfaces may show small yellow granules, Fordyce spots. Fordyce spots are superficially located sebaceous glands. The uterine round ligaments pass through the inguinal canal to end in the deep fibrofatty tissue of the labia majora. The floors of the labia majora are the right and left superficial perineal (Colles') fasciae.

Labia Minora. The right and left labia minora (nymphae) are quite variable, symmetrical, or occasionally asymmetrical folds of loose fibroelastic tissue without fat. The lateral surfaces are covered by thin, moist, hairless, and pigmented skin. The medial surface may be covered by skin similar to the lateral surfaces or by mucosa. The labia minora are medial to and largely hidden by the labia majora. The medial surfaces appose each other and surround the vestibule of the vagina. The lateral boundaries are the interlabial sulci. The medial boundaries are Hart's lines, which are the visible boundaries between the pigmented skin and the bright pink mucosa. Hart's lines are usually at the bases of the labia minora, but are variable. Anteriorly, each labium minus divides into anterior and posterior parts. The anterior parts unite anteriorly to the glans clitoris to form the prepuce, and the posterior parts unite posteriorly to the clitoris to form the frenulum. The labia minora fuse posteriorly to form the fourchette. Fordyce spots may be seen on the labia minora.

Vestibule of the Vagina. The vestibule is the medial (central), mucosa-covered part of the vulva. On embryologic, anatomic, and architectonic grounds, the correct term is "vestibule of the vagina'' not "vulvar vestibule,'' as sometimes appears in the literature (2). The vestibule is composed of loose fibroelastic and smooth muscular tissue without fat. The boundaries of the vestibule are Hart's lines laterally, the hymenal ring medially, the frenulum of the clitoris anteriorly, the fourchette posteriorly, and Colles' fascia deeply. The vestibule contains the urethral meatus and vaginal opening in the midline. The ostia of the greater vestibular (Bartholin's) ducts may be seen with the naked eye in the five and seven o'clock positions just external to the hymen. Minute, soft, nonbranching, pink polyps, the vestibular papillae, are a normal finding in one-third of women in the reproductive age group, although uncommon after menopause (Fig. 1) (3). They may be acetowhite and must be distinguished from condylomata acuminata. Compared to condylomata acuminata, vestibular papillae are pinker, soft, and nonbranched.

Hymen. The hymen is a diaphragm of loose fibrous tissue covered on both sides by mucous membrane that demarcates the vestibule from the vagina. Before first intercourse, the hymen is of variable shape, but often crescentic and covering only the posterior margin of the vaginal orifice. Less commonly, it may be more complete, but usually still contains one or two openings. At first intercourse, there will often be tearing of the hymen to produce fissures. The appearance of the hymen has been used since time immemorial to determine whether penetration has taken place; however, recent studies of prepubertal non-sexually abused girls indicate a wide range of normal appearance (4,5). Changes that were considered the result of sexual abuse, including a gaping introitus, may be seen in nonabused girls, and may be difficult to distinguish from changes induced by sexual penetration. The tags of mucous membrane following fissuring of the hymen are called the caruncles hymenalis or carunculae myrtiformes.

Figure 1 Vestibular papillomatosis: multiple small nonbranching fronds around the introitus. Source: Courtesy of Dr. Ross Pagano, Carlton, Victoria, Australia.

Urethral Meatus. The urethral meatus lies in the midline between the clitoris and the vaginal opening. Its anteroposterior position is quite variable, but it is usually 20 to 30 mm below the glans. The meatus may be everted and may show two or three folds, which become more prominent after menopause. The ostia of the paraurethral glands are not visible to the naked eye.

Clitoris, Superficial Part. The clitoris is composed of the body and crura. The crura are deep impalpable structures. The body can be felt beneath its prepuce, but the only part that is exposed is its terminal portion, the glans. The glans is a smooth-surfaced pink nodule covered by moist, thin hairless skin, which lies in the midline anterior to the urethral meatus. Resting clitoral size varies according to the age of the female, parity, and hormonal status (6). Anatomically, the body of the clitoris is about 40 mm long. Clinically, however, the total length of the glans and body is only 16.3 ± 4.3 mm, the transverse diameter of the glans is 3.4 ± 1mm, and the length of the glans is 5.1 ± 1.4 mm (7).

Fossa Navicularis. The fossa navicularis is a shallow depression in the vestibule that lies posterior to the vaginal orifice. Its boundaries are anterior, the hymen; posterior, the fourchette, and lateral, the labia minora. It is composed of squamous mucosa overlying a thick lamina propria of loose fibrous and deep fibrous tissue and smooth muscular tissue.

Perineum. The clinical perineum is the skin between the vulva and the anus. It is composed of hair-bearing skin apart from a variably broad hairless strip in the midline and deep fibromuscular tissue. In the midline, the perineal body can be palpated beneath the skin.

Deep Anatomy

Colles' Fascia. The vulva is subdivided into superficial and deep compartments by bilateral transverse fibrous sheets, Colles' (superficial perineal) fasciae, which are the continuation of the deep fascia of the anterior abdominal wall. The superficial compartment contains skin, skin appendages, and fibromuscular tissue or subcutaneous fat, depending on the site. The deep compartment, the superficial perineal pouch or space, contains the deep part of the body and all of the crura of the clitoris, membranous urethra, vestibular bulbs, greater vestibular (Bartholin's) glands, three pairs of skeletal muscles, and the perineal body. The paired structures and perineal body are contained in fat and/or fibrous tissue.

Inferior Fascia of the Urogenital Diaphragm. The perineum is separated from the pelvis by the urogenital diaphragm. The urogenital diaphragm is composed of the muscles of the levator ani covered superiorly and inferiorly by fasciae. The deep boundary of the vulva is the inferior fascia of urogenital diaphragm or perineal membrane. The crura, bulbs, and bulbospongiosus muscles attach to the inferior fascia of the urogenital diaphragm.

Suspensory Ligament of the Clitoris. The suspensory ligament of the clitoris is a thick, multiplanar, fan-shaped fibrofatty sheet, which extends from the deep fascia of the mons pubis to converge on the body of the clitoris (8). The ligament has superficial and deep components. The superficial component is 70 to 80 mm wide in the mons and 80 to 90 mm long. It attaches to the clitoral body, glans, and medial labia minora. The deep component is up to 10 mm thick and more fibrous. It has a narrow origin from the pubic symphysis and converges on the superolateral clitoral body. After reaching the clitoris, the suspensory ligament divides into right and left arms, which continue posteriorly to reach the labia and bulbs.

Clitoris, Deep Part. Anatomically, the clitoris is much larger than clinically apparent because most of it is deep to the skin. Recent dissections describe it is a triplanar structure projecting 4 to 6 cm anterior to the pubis (6). The body is located in the midline, at the anterior junction of the labia minora, anterior to the vestibule. Only the terminal glans is exposed. The remainder of the body is covered by its prepuce anteriorly and frenulum posteriorly, which are derived from the labia minora. The body is curved with its convexity anterior. It is formed by the fusion of two cylindrical masses of spongy tissue, the corpora cavernosa. A dense fibrous sheath encloses each corpus cavernosum and forms an incomplete septum between the two. The corpora cavernosa separate posteriorly to form the crus of the clitoris. The arms of the crura are up to 90 mm long, lie along, and insert into the inferior borders of the ischiopubic rami of the pubic arch. They also partly insert into the inferior fascia of the urogenital diaphragm. The arms of the right and left crus are covered by the ischiocavernosus muscles. The clitoris is stabilized by the suspensory ligament.

Bulbs of the Vestibule. The vestibular bulbs are paired masses of erectile (spongy) tissue closely related to the anterior and lateral walls of the distal urethra and lateral walls of the distal vagina. When stimulated, the erect bulbs narrow the introitus to aid sexual intercourse. Anteriorly, the bulbs attach to the clitoral body and to each other beneath the clitoris as a narrow bridge anterior to the urethra. They then expand and descend posterolaterally in the superficial perineal pouch to form cylindrical masses in the deep lateral wall of the vagina at the level of the intro-itus. The degree of posterior extension is variable and may depend upon age (6). The bulbs are usually about 30 mm long and reach at least the three and nine o'clock positions. The bulbs are covered superficially and laterally by the bulbospongiosus muscles and deeply by the perineal membrane (urogenital diaphragm), into which they insert.

Major Vestibular (Bartholin's) Glands. The major vestibular (Bartholin's) glands are mucinous glands that secrete mucus under parasympathetic stimulation during sexual arousal to aid intercourse. The glands are normally impalpable and not identified during surgical procedures. They are paired 5 to 10 mm rounded bodies that lie in the superficial perineal pouch covered in mixed fibrous and smooth muscle tissue, at the posterior end of the bulbs, and covered by the bulbs and bulbos-pongiosus muscles. The ducts, which are just visible to the naked eye, open into the vestibule, very close to the hymen at five and seven o'clock of the introitus.

Superficial Perineal Muscles. Three pairs of skeletal muscles, the ischiocaver-nosus, bulbospongiosus, and superficial transversus perinei muscles, form an incomplete muscular sheet in the superficial perineal pouch (1). These muscles form bilateral triangles with the clitoris, perineal body, and ischial tuberosities as the points. The ischiocavernosus muscles arise from medial surface of the ischial bones, overlie the arms of the crura, and join anteriorly to the body of the clitoris, into which they also insert. The bulbospongiosus muscles arise from the perineal body, overlie the greater vestibular (Bartholin's) glands and bulbs, and fuse just posterior to the clitoris, into which they also insert. The superficial transversus perinei muscles arise from the medial surface of the ischial bones and extend transversely to insert into the perineal body. The ischiocavernosus and bulbospongiosus muscles overlie erectile tissue and their contraction helps with female erection. The bulbs ospongiosus muscles are also weak vaginal constrictors, the main vaginal constrictor being the levator ani. The transversus perinei muscles help stabilize the perineal body.

Urogenital Diaphragm. The urogenital diaphragm remains a controversial subject. According to Mostwin, it is a continuous fan-shaped mass of skeletal muscles forming part of the levator ani and divided into various parts depending upon its origins and insertions (9). It is orientated transversely and covers the anterior surface of the urethra and distal vagina. The extent to which the fibers encircle the vagina or urethra depends upon the level at which a transverse section is taken through the structures. Beginning anteroinferiorly, the skeletal muscle almost completely surrounds the distal vagina, being deficient only posteriorly. Superoposteriorly, the muscle fibers insert progressively more anteriorly, until, at the level of the proximal one-third of the urethra, the muscle no longer encircles any part of the vagina, but completely encircles the urethra, being thicker anteriorly.

Perineal Body. The perineal body (central tendon of the perineum) is an ill-defined pyramidal-shaped mass of mixed smooth muscle and fibrous tissue between the vagina and the anus. The apex is directed superiorly and base toward the perineal skin. There is only a small amount of subcutaneous fat between the perineal body and the skin. The perineal body serves as a site of attachment for skeletal muscles and fasciae of the perineum. The muscular attachments are the levator ani, urethral sphincters, deep transversus perinei, external anal sphincter, peripheral fibers of the longitudinal smooth muscle of the rectum, bulbospongiosus, and superficial transversus perinei muscles. The fascial attachments are the superior and inferior urogenital diaphragm fasciae and superficial perineal (Colles') fascia.

Arteries. The arterial supply to the vulva comes from branches of the internal iliac and femoral arteries. The internal iliac artery gives rise to the internal pudendal artery, which supplies the medial and deep parts of the vulva, including the erectile tissues, and shares the supply to the labia (1). The internal pudendal artery enters the perineum from the buttock via the lesser sciatic foramen. It passes anteromedially along the ischiopubic ramus within the deep perineal space within a fascial compartment (Alcock's canal) and gives rise to the inferior rectal, perineal, and bulbar arteries before dividing to form the deep and dorsal arteries of the clitoris. These branches pierce the inferior fascia of the urogenital diaphragm to enter the superficial perineal space. The artery of the bulb of the vestibule and the anterior vaginal artery supply the bulb and greater (Bartholin's) gland. The dorsal clitoral artery runs alongside the dorsal nerves to terminate in the glans. The deep artery of the clitoris supplies the crus. The femoral artery gives off the superficial and deep external pudendal arteries to supply the majority of arterial blood to the skin and superficial fascia of the vulva. The external pudendal artery travels from the groin with the round ligament to enter the labia majora where it anastomoses with the labial branches of the internal pudendal artery.

Veins. Blood is drained from the perineum mainly by the internal pudendal veins, but some is drained by the deep dorsal vein of the clitoris and returned to the vesical plexus or by the external pudendal veins into the great saphenous veins (1). Venous vessels follow the branches of the internal and external pudendal arteries and are named accordingly. Veins from the bulbs of the vestibule, labia majora, and anal canal unite to form two venae comitantes of the internal pudendal artery called the internal pudendal veins. The internal pudendal veins empty into the internal iliac veins. There are no corresponding veins for the deep arteries of the clitoris, and most of the blood from the glans of the clitoris is drained to the deep dorsal vein of the clitoris, an unpaired vessel that runs between the two dorsal arteries. The deep dorsal vein drains into the vesical plexus and communicates with the internal pudendal vein tributaries. The external pudendal veins provide additional drainage from the labia majora and empty into the great saphenous veins.

Lymph. The lymphatic drainage of the anal canal, perineal skin, distal urethra, and vulva follows the branches of the external pudendal blood vessels to the inguinal lymph nodes and then to the external iliac, common iliac, and para-aortic lymph nodes (1). Midline structures, defined as anterior to urethra or posterior to the fourchette, have bilateral lymphatic drainage. The groin lymph nodes consist of superficial and deep groups, depending on whether they are superficial or deep to the femoral fascia (10). The superficial group is further divided into upper and lower groups. The upper superficial nodes are found along the line of the inguinal ligament, and the lower along the terminal part of the great saphenous vein. The deep nodes, one to three in number, lie in the fossa ovalis, medial to the femoral vein. The superficial group most often contains the sentinel node or nodes, but as in other sites, sentinel node studies demonstrate occasional marked variation in lymphatic drainage that cannot be predicted clinically. Lymphatic vessels of the deep perineum, including the deep perineal space, membranous urethra, and upper vagina follow the internal pudendal vessels to the internal iliac nodes.

Nerves. The motor and sensory somatic and autonomic nerve supply to the vulva is derived from L1 to S4 (1). The pudendal nerves supply the somatic motor and sensory nerves to most of the vulva, distal vagina, and anal canal. The right and left pudendal nerves are formed from the S2 to S4 anterior rami of the sacral plexus. Each pudendal nerve travels alongside the internal pudendal artery to give off similarly named branches. The pudendal nerve gives rise to the inferior rectal (hemorrhoidal) nerve, which innervates the external anal sphincter, lower anal canal, and perianal skin. At the posterior margin of the urogenital diaphragm, it divides to form the perineal nerve and the dorsal nerve of the clitoris. The perineal nerve subdivides into many muscular branches and two cutaneous nerves. The two cutaneous branches, the posterior labial branches, pass anteriorly in the superficial perineal space to supply sensory innervation to the posterior labia majora. The mons pubis and anterior labia majora are innervated by the anterior labial nerve (branch of the ilioinguinal nerve), derived from the lumbar plexus. The paired dorsal nerves of the clitoris run alongside the dorsal arteries of the clitoris in the deep perineal space to supply the corpora cavernosa, anterior labia minora, and glans.

Parasympathetic fibers enter the perineum through the urogenital hiatus along with the branches of the vesical plexus and cavernous nerves. Parasympathetic sensory nerves monitor a sense of fullness of the anal canal and vagina. Parasympathetic motor function increases vaginal secretions and causes erection.

Vagina

The vagina is a muscular tube, 70 to 90 mm long, posterior to the urethra and bladder, and anterior to the rectum. It extends from the hymenal ring to the cervix. The upper half is curved anteriorly to lie on the bladder. Proximally, the vagina is covered by peritoneum posteriorly. The upper vagina is attached posteriorly to the uterosacral ligaments, laterally to the cardinal ligaments, and anteriorly to the base of the bladder. The cervix projects downwards and backwards through the upper anterior vaginal wall, and shortens the anterior wall by 20 mm, compared to the posterior wall. The circumferential recess formed by the angle between the projecting cervix and the upper vagina is the fornix, which is divided into anterior (shallow), posterior (deep), and lateral components. At the upper end, the cervix holds the vagina open, but most of the resting vagina is collapsed with its anterior wall in contact with the posterior wall to form a H- or crescent shape on cross section. The urethra is attached to the anterior vaginal wall. The lower one-third of the vagina passes through the urogenital diaphragm. Below the diaphragm, the vagina is supported by the perineal body and perineal muscles.

The vagina is composed of three layers: mucosa, muscularis, and perimuscular layers. The mucosa is rugose, with the degree of rugosity depending on hormonal status. The muscularis is thin. In the lower vagina, the perimuscular layer is directly continuous laterally with the vestibular bulbs.

The lymphatic drainage of the upper two-thirds of the vagina follows that of the cervix to the internal and external iliac nodes. The lower one-third drain follows that of the vulva to the superficial inguinal nodes.

Urethra

The female urethra is a muscular tube 4 cm long and 6 mm in diameter. The urethra begins at the internal urethral orifice on the anterior urinary bladder wall. It is composed of long, upper pelvic and short, lower perineal parts. For the great part of its length, the pelvic urethra travels anteroinferiorly behind the pubic symphysis. It is attached to the vagina at the vaginocervicourethral angle and at the distal two-thirds. The space between these two attachments is the vesicovaginal space, which contains loose connective tissue. The pelvic urethra passes through the urogenital diaphragm to emerge as the perineal urethra, which ends as the external urethral orifice (urinary meatus). The perineal urethra is almost surrounded by the vestibular bulbs, apart from the posterior aspect. The urethra is normally collapsed and has longitudinal grooves allowing its lumen to be distensible. It is composed of a mucosa and a muscle coat, which consists of smooth muscle with an inner layer of longitudinal bundles and a middle layer with circular bundles (internal urethral sphincter) externally intermingled with circularly orientated striated muscle (external urethral sphincter). The internal sphincter is continuous with the vesical sphincter and, at the outside, with longitudinal extensions of the detrusor muscle of the bladder wall. The external urethral sphincter completely surrounds the upper two-thirds of the urethra, although it is thinner between the urethra and the vagina. It can be felt within the vagina as a transverse ridge beneath the mucosa anteriorly.

The blood supply, innervation, and lymphatic drainage of the pelvic urethra are the same as that of the bladder neck. The perineal urethra, like the vulva, is supplied by the pudendal vessels and nerves, and the lymphatic drainage is to the inguinal nodes.

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Responses

  • patrick reinhard
    Is it normal if vestibular bulb is visible of left labia Minora?
    3 years ago
  • carrie
    What anatomic space communicates with vulva?
    2 years ago

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