Mons pubis

The mons pubis is the rounded hair-bearing area of skin over the pubic symphysis and adjacent pubic bone. It is formed by a mass of subcutaneous adipose connective tissue. Before puberty, the mons pubis is relatively flat and the labia minora are poorly formed. During adolescence, coarse hair forms over the mons and labia majora and the labia minora become more prominent and flap like. In adults, the mons is covered by coarse hair that is usually limited above by a horizontal boundary; in males there is a continuation of pubic hair to the umbilicus. After the menopause, pubic hair thins and labial tissue atrophies slightly.

Labia majora

The labia majora are two prominent, longitudinal folds of skin that extend back from the mons pubis to the perineum (Fig. 77.1B). They form the lateral boundaries of the vulva. Each labium has an external, pigmented surface covered with hairs and a smooth, pink internal surface with large sebaceous follicles. Between these surfaces there is loose connective and adipose tissue, intermixed with smooth muscle (resembling the scrotal dartos muscle), vessels, nerves and glands. The uterine round ligament may end in the adipose tissue and skin in the anterior part of the labium. A persistent processus vaginalis and congenital inguinal hernia may also reach a labium. The labia are thicker anteriorly, where they join to form the anterior commissure. Posteriorly they do not join, but instead merge into neighbouring skin, ending near and almost parallel to each other. The connecting skin between them posteriorly forms a ridge, the posterior commissure, that overlies the perineal body and is the posterior limit of the vulva. The distance between this and the anus is 2.5–3 cm thick and is termed the ‘gynaecological’ perineum.

Labia minora

The labia minora are two small cutaneous folds, devoid of fat, that lie between the labia majora. They extend from the clitoris obliquely down, laterally and back, flanking the vaginal orifice. Anteriorly, each labium minus bifurcates. The upper layer of each side passes above the clitoris to form a fold, the hood or prepuce, which overhangs the glans of the clitoris. The lower layer of each side passes below the clitoris to form the frenulum of the clitoris (Fig. 77.1A,C). Sebaceous follicles are numerous on the apposed labial surfaces. Sometimes an extra labial fold (labium tertium) is found on one or both sides between the labia minora and majora.

Vestibule

The vestibule is the cavity that lies between the labia minora. It contains the vaginal and external urethral orifices and the openings of the two greater vestibular (Bartholin’s) glands and of numerous mucous, lesser vestibular glands. There is a shallow vestibular fossa between the vaginal orifice and the frenulum of the labia minora.

Bulbs of the vestibule

The bulbs of the vestibule lie on each side of the vestibule. They are two elongated masses of erectile tissue, 3 cm long, which flank the vaginal orifice and unite anterior to it by a narrow commissura bulborum (pars intermedia). Their posterior ends are expanded and are in contact with the greater vestibular glands. Their anterior ends taper and are joined by a commissure and also to the clitoris by two slender bands of erectile tissue. Their deep surfaces contact the inferior aspect of the urogenital diaphragm, and superficially each is covered by bulbospongiosus posteriorly (Fig. 77.2A–C).

Fig. 77.2 A, Muscles of the vestibule and clitoris. B, Erectile tissues of the clitoris. C, Erectile tissues of clitoris, vestibule and greater vestibular gland with a surface anatomy overlay.

(A, B adapted from Drake, Vogl and Mitchell 2005. C from Drake, Vogl and Mitchell 2005.)

Clitoris

The clitoris is an erectile structure partially enclosed by the anterior bifurcated ends of the labia minora. It has a root, a body, and a glans. The body can be palpated through the skin. It contains two corpora cavernosa, composed of erectile tissue and enclosed in dense fibrous tissue, and separated medially by an incomplete fibrous pectiniform septum. The fibrous tissue forms a suspensory ligament that is attached superiorly to the pubic symphysis. Each corpus cavernosum is attached to its ischiopubic ramus by a crus that extends from the root of the clitoris. The glans clitoris is a small round tubercle of spongy erectile tissue at the end of the body and connected to the bulbs of the vestibule by thin bands of erectile tissue. It is exposed between the anterior ends of the labia minora. Its epithelium has high cutaneous sensitivity, important in sexual responses (Fig. 77.2).

Vascular supply and lymphatic drainage of the vulva

Arteries

The arterial blood supply of the female external genitalia is derived from the superficial and deep external pudendal branches of the femoral artery and the internal pudendal artery on each side (Fig. 77.3A).

Fig. 77.3 Vessels (A), nerves and lymphatics (B) of the female pelvis. Sagittal view.

(From Sobotta 2006.)

Innervation

The innervation to the lower genital tract is shown in Fig. 77.5 and Table 77.1.

Fig. 77.5 Innervation of the female reproductive system.

(From Sobotta 2006.)

Table 77.1 Innervation of female genitalia.

The sensory innervation of the anterior and posterior parts of the labium majus differ. The anterior third of the labium majus is supplied by the ilioinguinal nerve (L1), the posterior two-thirds are supplied by the labial branches of the perineal nerve (S3), and the lateral aspect is also innervated by the perineal branch of the posterior cutaneous nerve of the thigh (S2).

Vascular supply and lymphatic drainage

Innervation

The lower vagina is supplied by the pudendal nerve (S2, S3 and S4). The upper vagina is supplied by the splanchnic nerves (S2, S3 and sometimes S4).

Microstructure

The vagina has an inner mucosal and an external muscular layer. The mucosa adheres firmly to the muscular layer. There are two median longitudinal ridges on its epithelial surface, one anterior and the other posterior. Numerous transverse bilateral rugae extend from these vaginal columns. They are divided by sulci of variable depth, giving an appearance of conical papillae, which are most numerous on the posterior wall and near the orifice, and which are especially well developed before parturition. The epithelium is non-keratinized, stratified, squamous similar to, and continuous with, that of the ectocervix. After puberty it thickens and its superficial cells accumulate glycogen, which gives them a clear appearance in histological preparations.

Fig. 77.4 Muscles, vessels and nerves of the female perineum. Inferior view.

(From Sobotta 2006.)

The vaginal epithelium does not change markedly during the menstrual cycle, but its glycogen content increases after ovulation and then diminishes towards the end of the cycle. Natural vaginal bacteria, particularly Lactobacillus acidophilus, break down glycogen in the desquamated cellular debris to lactic acid. This produces a highly acidic (pH 3) environment, which inhibits the growth of most other microorganisms. The amount of glycogen is less before puberty and after the menopause, when vaginal infections are more common. There are no mucous glands, but a fluid transudate from the lamina propria and mucus from the cervical glands lubricate the vagina (Fig. 77.8). The muscular layers are composed of smooth muscle and consist of a thick outer longitudinal and an inner circular layer. The two layers are not distinct but connected by oblique interlacing fibres. Longitudinal fibres are continuous with the superficial muscle fibres of the uterus. Half way along the vagina is a U-shaped muscular sling, called the pubo-vaginalis. The lower vagina is also surrounded by the skeletal muscle fibres of bulbospongiosus. A layer of loose connective tissue, containing extensive vascular plexuses, surrounds the muscle layers.

Fig. 77.8 Stratified squamous non-keratinizing epithelium (E) covering the ectocervix and vagina. The cells of the middle and upper layers appear clear due to their content of glycogen.

(By courtesy of Mr Peter Helliwell and Dr Joseph Mathew, Department of Histopathology, Royal Cornwall Hospitals Trust, UK.)

Body

The body of the uterus is pear shaped and extends from the fundus superiorly to the cervix inferiorly. Near its upper end, the uterine tubes enter the uterus on both sides at the uterine cornua. Inferoanterior to each cornu is the round ligament and inferoposterior is the ovarian ligament. The dome-like fundus is superior to the entry points of the uterine tubes and covered by peritoneum which is continuous with that of neighbouring surfaces. The fundus is in contact with coils of small intestine and occasionally by distended sigmoid colon. The lateral margins of the body are convex, and on each side their peritoneum is reflected laterally to form the broad ligament, which extends as a flat sheet to the pelvic wall (Fig. 77.13). The anterior surface of the uterine body is covered by peritoneum which is reflected onto the bladder at the uterovesical fold (Fig. 77.14). This normally occurs at the level of the internal os, the most inferior margin of the body of the uterus. The vesico-uterine pouch between the bladder and uterus is obliterated when the bladder is distended, but may be occupied by small intestine when the bladder is empty. The posterior surface of the uterus is convex transversely. Its peritoneal covering continues down to the cervix and upper vagina and is then reflected back to the rectum along the surface of the recto-uterine pouch (of Douglas), which lies posterior to the uterus (Fig. 77.15). The sigmoid colon and occasionally the terminal ileum lie posterior to the uterus.

Fig. 77.13 Laparoscopic view of the broad ligament.

Fig. 77.14 Laparoscopic view of the anterior part of the pelvis showing uterovesical fold anterior to the uterus.

Fig. 77.15 Laparoscopic view of the posterior pelvis showing the pouch of Douglas (recto-uterine pouch) with the sigmoid colon descending towards the rectum.

The cavity of the uterine body usually measures 6 cm from the external os of the cervix to the wall of the fundus and is flat in its anteroposterior plane. In coronal section, it is triangular, broad above where the two uterine tubes join the uterus, and narrow below at the internal os of the cervix (Fig. 77.16).

Fig. 77.16 Hysteroscopic view of the endometrial cavity of the uterus.

There may be failure in fusion of the paramesonephric (Müllerian) ducts, which results in a uterus that is not pear shaped. There may just be a septum (septate uterus) or partial clefting of the uterus (bicornuate uterus); the most extreme example is a septate vagina, two cervices, and two discrete uteri, each with one uterine tube (uterus didelphys).

Cervix

The adult, non-pregnant cervix is narrower and more cylindrical than the body of the uterus and is typically 2.5 cm long. The upper end communicates with the uterine body via the internal os and the lower end opens into the vagina at the external os. In nulliparous women, the external os is usually a circular aperture, whereas after childbirth it is a transverse slit. Two longitudinal ridges, one each on its anterior and posterior walls, give off small oblique palmate folds that ascend laterally like the branches of a tree (arbor vitae uteri): the folds on opposing walls interdigitate to close the canal. The narrower isthmus forms the upper third of the cervix. Although unaffected in the first month of pregnancy, it is gradually taken up into the uterine body during the second month to form the ‘lower uterine segment’ (see below). In non-pregnant women the isthmus undergoes menstrual changes, although these are less pronounced than those occurring in the uterine body. The external end of the cervix enters the upper end of the vagina, thereby dividing the cervix into supravaginal and vaginal parts. The supravaginal part is separated anteriorly from the bladder by cellular connective tissue, the parametrium, which also passes to the sides of the cervix and laterally between the two layers of the broad ligaments.

Pelvic ligaments and peritoneal folds

The uterus is connected to a number of ‘ligaments’. Some are true ligaments in that they have a fibrous composition and provide support to the uterus, some provide no support to the uterus, and others are simply folds of peritoneum.

Peritoneal folds

The parietal peritoneum is reflected over the upper genital tract to produce anterior (uterovesical), posterior (rectovaginal) and lateral peritoneal folds. The lateral folds are commonly called the broad ligaments.

Uterovesical and rectovaginal folds

The anterior or uterovesical fold consists of peritoneum reflected onto the bladder from the uterus at the junction of its cervix and body. The posterior or rectovaginal fold consists of peritoneum reflected from the posterior vaginal fornix on to the front of the rectum, thereby create the deep recto-uterine pouch of Douglas. The pouch of Douglas is bounded anteriorly by the uterus, supravaginal cervix and posterior vaginal fornix, posteriorly by the rectum and laterally by the uterosacral ligaments.

Broad ligament

The lateral folds or broad ligaments extend on each side from the uterus to the lateral pelvic walls, where they become continuous with the peritoneum covering those walls (Figs 77.17, 77.18). The upper border is free and the lower border is continuous with the peritoneum over the bladder, rectum and pelvic side-wall. The borders are continuous with each other at the free edge via the uterine fundus and diverge below near the superior surfaces of levatores ani. A uterine tube lies in the upper free border on either side. The broad ligament is divided into an upper mesosalpinx, a posterior mesovarium and an inferior mesometrium.

Fig. 77.17 Pelvic peritoneal reflections, demonstrating the broad ligament and its contents.

(From Drake, Vogl and Mitchell 2005.)

Fig. 77.18 Ovaries and broad ligament, superior view with the uterus lifted away from the bladder.

(From Sobotta 2006.)

Mesosalpinx

The mesosalpinx is attached above to the uterine tube and posteroinferiorly to the mesovarium. Superior and laterally it is attached to the suspensory ligament of the ovary and medially it is attached to the ovarian ligament. The fimbria of the tubal infundibulum projects from its free lateral end. Between the ovary and uterine tube the mesosalpinx contains vascular anastomoses between the uterine and ovarian vessels, the epoophoron, and the paroophoron (Fig. 77.19). The mesovarium projects from the posterior aspect of the broad ligament, of which it is the smaller part. It is attached to the hilum of the ovary and carries vessels and nerves to the ovary.

Fig. 77.19 Broad ligament (left) and blood supply to the uterus and ovaries (right).

(From Drake, Vogl, Mitchell, Tibbitts and Richardson 2008.)

Mesometrium

The mesometrium is the largest part of the broad ligament, and extends from the pelvic floor to the ovarian ligament and uterine body. The uterine artery passes between its two peritoneal layers typically 1.5 cm lateral to the cervix: it crosses the ureter shortly after its origin from the internal iliac artery and gives off a branch that passes superiorly to the uterine tube, where it anastomoses with the ovarian artery (Fig. 77.19). Between the pyramid formed by the infundibulum of the tube, the upper pole of the ovary, and the lateral pelvic wall, the mesometrium contains the ovarian vessels and nerves lying within the fibrous suspensory ligament of the ovary (infundibulopelvic ligament). This ligament continues laterally over the external iliac vessels as a distinct fold. The mesometrium also encloses the proximal part of the round ligament of the uterus, as well as smooth muscle and loose connective tissue.

Ligaments of the pelvis

The ligaments of the pelvis consist of the round, uterosacral, transverse cervical and pubocervical ligaments.

Uterosacral, transverse cervical and pubocervical ligaments

The uterosacral ligaments are recto-uterine folds and contain fibrous tissue and smooth muscle (Fig. 77.18). They pass back from the cervix and uterine body on both sides of the rectum, and they are attached to the front of the sacrum. The ligaments can be palpated laterally on rectal examination. On vaginal examination they can be felt as thick bands of tissue passing downwards on both sides of the posterior fornix. The transverse cervical ligaments (cardinal ligaments, ligaments of Mackenrodt) (Fig. 77.20) extend from the side of the cervix and lateral fornix of the vagina to attach extensively on the pelvic wall. At the level of the cervix, some fibres interdigitate with fibres of the uterosacral ligaments. They are continuous with the fibrous tissue around the lower parts of the ureters and pelvic blood vessels. Fibres of the pubocervical ligament pass forward from the anterior aspect of the cervix and upper vagina to diverge around the urethra (Fig. 77.20). These fibres attach to the posterior aspect of the pubic bones.

Fig. 77.20 Supporting ligaments of the pelvis showing the transverse cervical ligaments.

(From Sobotta 2006.)

While the uterosacral and transverse cervical ligaments may act in varying measure as mechanical supports of the uterus, levatores ani and coccygei, the urogenital diaphragm and the perineal body appear at least as important in this respect. There has been renewed interest in the supporting structures of the pelvis, and the subject has been reviewed in detail by Delancey (2000).

Vascular supply and lymphatic drainage

Arteries

The arterial supply to the uterus comes from the uterine artery (Fig. 77.21). This arises as a branch of the anterior division of the internal iliac artery. From its origin, the uterine artery crosses the ureter anteriorly in the broad ligament before branching as it reaches the uterus at the level of the cervico-uterine junction. One major branch ascends the uterus tortuously within the broad ligament until it reaches the region of the ovarian hilum, where it anastomoses with branches of the ovarian artery. Another branch descends to supply the cervix and anastomoses with branches of the vaginal artery to form two median longitudinal vessels, the azygos arteries of the vagina, which descend anterior and posterior to the vagina. Although there are anastomoses with the ovarian and vaginal arteries, the dominance of the uterine artery is indicated by its marked hypertrophy during pregnancy.

Fig. 77.21 A, Normal arterial supply to uterus, uterine tubes and ovaries. B–F, Variant arterial supply.

(From Sobotta 2006.)

The tortuosity of the vessels as they ascend in the broad ligaments is repeated in their branches within the uterine wall. Each uterine artery gives off numerous branches. These enter the uterine wall, divide and run circumferentially as groups of anterior and posterior arcuate arteries. They ramify and narrow as they approach the anterior and posterior midline so that no large vessels are present in these regions. However, the left and right arterial trees anastomose across the midline and unilateral ligation can be performed without serious effects. Terminal branches in the uterine muscle are tortuous and are called helical arterioles. They provide a series of dense capillary plexuses in the myometrium and endometrium. From the arcuate arteries many helical arteriolar rami pass into the endometrium. Their detailed appearance changes during the menstrual cycle. In the proliferative phase helical arterioles are less prominent, whereas they grow in length and calibre, becoming even more tortuous in the secretory phase.

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