Clinical Anatomy of the Uterus, Fallopian Tubes, & Ovaries
Craig W. Muckle
Craig W. Muckle, MD (Deceased)
The female organs of generation include the uterus, fallopian tubes (oviducts), and the ovaries (Fig. 1). Their position, size, and anatomic relations vary considerably with age and the physiologic changes of menstruation, pregnancy, the menopause, and senility.
At puberty the uterus may be slightly more than 2 inches in length. After menstruation has been established, it is approximately 3 inches long. Pregnancy, of course, causes considerable enlargement with subsequent involution, while the uterus of postmenopausal women becomes atrophic and shrunken. In the mature woman the uterus is approximately 7.5 cm long, 5 cm wide, and 2.5 cm thick and weighs 30 to 40 gm. This is more easily remembered as 1 inch thick, 2 inches wide, and 3 inches long, the rule of “1–2-3.”
The uterus is shaped like an inverted pear. The main pan is called the body or corpus; the portion extending into the vagina is called the neck or cervix. The upper part of the uterus above the insertion of the tubes is the fundus. The narrow portion situated between corpus and cervix is known as the isthmus and lies approximately at the level of the course of the uterine artery and the internal os of the cervix.
The cervix, most of which protrudes into the vagina, is 2 to 3 cm long. The intravaginal portion of the cervix, known as the portio vaginalis, ordinarily is covered with squamous epithelium with a number of mucus-secreting glands (Fig. 2). The external os is shaped like the crater of a volcano. Above the external os lies the fusiform endocervical canal, approximately 2 cm long and lined with columnar epithelium and endocervical glands. At the upper end of this canal at the junction with the uterine cavity is the internal os. The endocervical canal in the nullipara is lined by mucosa arranged in a series of folds. A vertical fold is present on the anterior and posterior cervical walls; from these, oblique folds radiate. These folds have been called the arbor vitae uteri or plicae palmatae. It was formerly thought that tubular glands descend vertically from the surface and divide into many branches forming compound racemose glands; however, secondary changes caused by the intense growth activity of the columnar cells result in the formation of tunnels, secondary clefts, and exophytic processes.
The uterine cavity lies above the internal cervical os. It is roughly triangular in shape and measures approximately 3.5 cm in length. Ordinarily, the anterior and posterior walls of the uterus lie in apposition so that little if any actual cavity is present. At each cornu or horn of the uterus, its cavity is continuous with the lumen of a fallopian tube.
In a considerable number of women the uterus is retroverted or retroflexed, a condition rarely of clinical significance. Particularly in parous women, the uterus may adopt a variety of positions, all of which must be considered normal. Lying upon the uterus are coils of intestines which, in the absence of adhesions, are continually changing their position.
The “positions” of the uterus are of considerable interest but of much less importance in gynecologic practice than 50 years ago. The normal position of the uterus is a nulligravid female is in moderate anteflexion or bent slightly anteriorly, and the uterus as a whole is inclined toward the symphysis in ante version against the bladder, adapting its position as the latter organ distends or empties (Fig. 3 and Fig. 4). In a variable number of women, perhaps a third, the uterus is retroverted or inclined posteriorly or retroflexed toward the sacrum. Quite a few disabilities were attributed to these “malpositions,” including dysmenorrhea, functional uterine bleeding, backache, dyspareunia, and leukorrhea. Many suspension operations were carried out, but these procedures are rarely employed at the present time. It should be mentioned that many normal uteri are in mid position, with the axis of uterus almost parallel to the spine. Prolapse of the uterus, by contrast, may be a real problem. If the cervix almost reaches the introitus, the prolapse is classified as first degree. A cervix visible at the introitus is considered a second-degree prolapse, while the protrusion of cervix and some of the corpus is called third-degree prolapse or procidentia. Before total hysterectomy became the usual procedure, a variety of operative procedures to support the uterus were employed; today, however, support operations without hysterectomy are unusual.
The peritoneum covers the uterus and is separated from the uterine musculature by a thin layer of periuterine fascia, which is a continuation and extension of the transversalis fascia. This mobile fascial layer is areolar tissue and is easily separated except :for a midline seam or raphe between the uterus and bladder anteriorly and between uterus and peritoneum posteriorly at the level of the isthmus. Posteriorly it sweeps down over the posterior vaginal wall and the cul-de-sac.
The musculature of the uterus is in several layers. There is an outer longitudinal layer (stratum supra-vasculare) continuing into the tubes and round ligaments. The vascular layer (stratum vasculare) consists of many interlacing spiral groups of smooth muscles and contains many blood vessels. An inner layer consists of muscle fibers arranged both longitudinally and obliquely.
The blood supply of the uterus is derived chiefly from the uterine arteries (Fig. 5). These arise from the hypogastric artery and swing toward the uterus, which they reach at approximately the level of the internal os (Fig. 6 and Fig. 7). Here the uterine arteries divide, the descending limb coursing downward along the cervix and lateral wall of the vagina. The ascending limb passes upward alongside the uterus and continues below the fallopian tube. Frequent anterior and posterior branches go to vagina, cervix, and uterus.
The ovarian artery, which ordinarily arises from the aorta, passes along the ovary, dividing into a number of branches. At several places in the broad ligament there are anastomotic connections between the tubal branch of the uterine artery and the ovarian artery. A branch of the uterine artery nourishes the round ligament. The veins in general accompany the arteries.
Using injection and microradiographic and histologic techniques, Farrer-Brown et al1 restudied the vascular anatomy of the uterus. Their studies showed that
They found that “each arcuate artery throughout its course gives off numerous branches running both centrifugally towards the serosa and centripetally towards the endometrium.” The arteries to the serosa at first were directed radially and then frequently became more circumferential. There is a plexus of small arterial radicals with a radial distribution located immediately below the serosa. The inner two thirds of the myometrium is supplied by tortuous radial branches of the arcuate arteries. They provide numerous branches terminating in a capillary network which surrounds groups of muscle fibers. An abrupt change in the density of the arterial pattern occurs at the junction of the basal layer of the endometrium with the subjacent myometrium. The endometrial vessels are relatively sparse in comparison with those of the myometrium at all stages of the menstrual cycle.
The uterus is partially supported by three pairs of ligaments. The most important are the paired cardinal (Mackenrodt's) or transverse cervical ligaments. Arising from the anterior and posterior marginal walls of the cervix, these ligaments fan out laterally to insert into the fascia overlying the obturator muscles and the levator ani muscles. The cardinal ligament forms the base of the broad ligament. Its muscles and connective tissue surround the uterine blood vessels as well as the accompanying nerves and lymphatics.
The paired round ligaments extend from the anterosuperior surface of the uterus through the internal inguinal rings and through the inguinal canals to end in the labia majors. They are composed of muscle fibers, connective tissue, blood vessels, nerves, and lymphatics. The round ligaments stretch with relative ease, particularly in pregnancy.
The uterosacral ligaments are condensations of fascia that arise from the posterior wall of the uterus at the level of the internal cervical os. They insert in the sacral fascia over the second and third sacral vertebrae. In addition to muscle and connective tissue, blood vessels, lymphatics, and parasympathetic nerve fibers are present.
The broad ligament is formed by folds of peritoneum covering the tubes, the infundibulopelvic vessels, and the hilus of the ovary. It contains a number of structures: tube, round ligament, ovarian ligament, uterine and ovarian blood vessels, nerves, lymphatics, and mesonephric remnants. Below the infundibulopelvic structures, the anterior and posterior leaves of peritoneum lie in apposition, leaving a clear space below the tube with its tubal branch of the uterine artery. This avascular area is useful to the surgeon in isolating the adnexal structures and in avoiding blood vessels while performing tubal ligations.
The endometrium varies greatly, depending on the phase of the menstrual cycle. In the proliferative phase immediately after menstruation, the surface of the mucosa is relatively smooth and lined with columnar epithelial cells, some of which may have cilia (Fig. 8). Uterine glands are straight or slightly curved and run an oblique course. The stroma is a reticular connective tissue with many spindle-shaped nuclei of mesenchymal cells in a reticulum of argyrophilic fibers.
The endometrium is considered to have three layers: the pars basalis, the zona spongiosa, and the superficial zona compacta. The straight branches of the radial arteries of the uterus terminate in capillaries in the basal layer, while the spiral or coiled branches penetrate to the surface epithelium, where they give rise to superficial capillaries. Sinus-like dilatations of the capillaries in the superficial layer are called “lakes.” These vascular lakes and capillaries are drained by small veins.
Proliferation of the endometrium occurs under the influence of estrogen; maturation occurs under the influence of progesterone. After formation of the corpus luteum, the endometrial glands grow, become tortuous, and secrete. The tubules grow laterally to join adjacent tubules. The spiral capillaries develop a terminal network of superficial capillaries. These changes result in the formation of a predeciduum prepared for the arrival of the trophoblast (Fig. 9). If there is no implantation of trophoblast, the levels of estrogen and progesterone fall and spasm of the spiral arteries results in ischemia and subsequent shedding of most of the endometrium, with associated bleeding.
Data on the lymphatic vessels of the uterus have been coordinated by Reynolds2. The entire uterus has a rich capillary bed as extensive as the blood capillary system. The lymphatic capillary bed is arranged in four zones: 1) the lower uterine segment with its rich supply of fine capillaries, 2) the subserosa of the corpus with a few lymphatics, 3) a deep subserosal network, and 4) a plentiful supply in the muscularis proper. These vessels increase greatly in number and size during pregnancy. The collecting system of the uterine lymphatics is formed from anastomoses of a lateral-uterine descending network of lymph vessels which unites with collecting vessels from the utero-ovarian pedicle and the external lilac area.
The fallopian tubes are bilateral muscular structures of paramesonephric duct origin. They are from 10 to 12 cm in length and usually less than 1 cm in diameter. The tubes or oviducts have a lumen that varies considerably in diameter. It is extremely narrow, being less than I mm at its opening into the uterine cavity. It is wider in the isthmus (Fig. 10) (2.5 mm) and in the ampulla (Fig. 11) is approximately 6 mm in diameter. The tube begins in the uterine cavity at the cornu and penetrates the myometrium (intramural or interstitial portion). The second portion is the relatively straight and narrow portion of the tube which emerges from the uterus posterior to and a little above the origin of the round ligament. The lumen of the narrow isthmus is relatively simple, with a few longitudinal folds. This portion of its tube is 2 or 3 cm long. There are three layers of musculature: the inner longitudinal, the middle circular layer, and the outer longitudinal layer. There is some evidence that the isthmus may act as a sphincter.
The ampulla is the largest and longest portion of the tube, approximately 5 or more cm in length. The lumen enlarges from 1 or 2 mm near the isthmus to over a centimeter at the distal portion. The mucosa has multiple longitudinal folds. The ampulla is the portion usually involved in gonorrheal salpingitis and tubo-ovarian abscesses and is the site of most ectopic pregnancies.
At the distal end of the tube is the trumpet shaped infundibulum. The tube ends in a number of fimbriae or fringelike processes. The largest of these is ordinarily in contact with the ovary and known as the ovarian fimbria. The peritoneal cavity in the female is connected with the exterior of the body through the patent distal end of the tube by way of the uterus and vagina. The ovum must enter through the open end of a tube if fertilization is to occur in the ampullary portion where sperm have collected by migrating “upstream” against the current. This opening is of considerable clinical importance as blood, ascending infections, or pus can pass out of the tube to invade the abdominal cavity, with resultant pain, endometriosis, or pelvic infection.
The epithelial lining of the tube has been studied extensively by light and electron microscopy. On light microscopic examination, four types of cells can be readily seen. Secretory cells or nonciliated cells have a heavily granular cytoplasm and an oval nucleus. The ciliated cells have a fine granular cytoplasm and are relatively square with a large round nucleus. The intercalary or “placed-between” cells are long narrow cells with dark nuclei causing them to be called “peg cells.” The fourth type of cells are the small “indifferent” cells with large dark nuclei.
Pauerstein3 has reviewed and summarized the numerous studies on tubal ultrastructure. Two basic types have been described, ciliated and secretory. The ciliated cells have a clear cytoplasm with vesicular reticulum. Microvilli are seen extending from the luminal edge of the cell. The cilia themselves have two central filaments and nine double, lateral filaments. Secretory cells have a dark cyto-plasm with fine granules. Darker secretory granules are prominent, with irregularly distributed endoplasmic reticulum. The tubal epithelium is responsive to the estrogen and progesterone levels during the menstrual cycle, pregnancy, and the menopause. The proliferative phase is characterized by elevated epithelium with ciliated and secretory cells of equal height. The luteal phase shows lower ciliated cells with higher and more prominent cytoplasm, sometimes with rupture and extrusion of the cytoplasm into the lumen. During menstruation and post menstruation, cells are lower and smaller. During pregnancy, tubal epithelium remains low. There is considerable variation in postmenopausal changes in the tubal epithelium. Apparently significant secretory activity ceases, but the onset of atrophy is variable and deciliation may not occur until years after the menopause.
The principal blood supply of the tube is from the upper end of the uterine artery, which bifurcates and sends a large branch or ramus below the tube to anastomose with the ovarian artery. The proximal two thirds of the tube is chiefly supplied by the uterine artery. The arterial supply is quite variable and there may be three branches (medial, intermediate, and lateral) or a branch from the uterine and another from the ovarian artery. Anastomoses between uterine and ovarian arteries in the mesosalpinx are variable but always present.
The venous system accompanies the arterial distribution. Capillary networks are to be found in subserosal, muscularis, and mucosal layers. The arrangement varies in different portions of the tube, but the venous plexuses become confluent in the subserosal layer. The lymphatic drainage runs along the upper edge of the broad ligament to the lymphatic network below the hilus of the ovary. From here the flow from uterus, tube, and ovary drains to the para-aortic or lumbar nodes.
The tube is provided with both sympathetic and parasympathetic innervation. Sympathetic fibers from T10 through L2 reach the inferior mesenteric plexus. Postganglionic fibers then pass to the oviduct. The fibers from the inferior mesenteric plexus pass to the cervicovaginal plexus, which in turn sends fibers to the isthmus and part of the ampulla. Some sympathetic fibers from T10 and T11 reach the celiac plexus and provide postganglionic fibers to the ovarian plexus, which supplies the distal ampulla and fimbriae. The parasympathetic supply is by vagal fibers from the ovarian plexus supplying the distal portion of the tube. Part of the isthmus receives its parasympathetic supply from S2, S3, and S4 via the pelvic nerve and the pelvic plexuses. The sympathetic innervation of the female pelvis is depicted in Fig. 12.
In the early embryo, differentiation of gonadal tissue occurs anterior to the mesonephros and along the entire medial aspect of the urogenital ridge. The cranial portions of the gonadal ridge degenerate, leaving an indifferent genital gland near the mesonephros. Primitive germ cells originate in the epithelial lining of the dorsal part of the hindgut. They migrate to the gonad and are seen as radial strands extending into the mesenchymal tissue. The migrating cells consist of primordial egg cells and prospective granulosa cells (Fig. 13).
The ovaries vary in shape, size, position, and appearance, depending on the age and the reproductive activities of the individual. The ovaries of a normal adult woman are 3 to 5 cm long, 1.5 to 3 cm wide, and 1 to 1.5 cm thick, with a weight of 3 to 8 gm (Fig. 14). Ordinarily the ovary is pink, but it may be pale blue at the site of a developing follicle, reddish purple at the site of a corpus hemorrhagicum, or yellow if a corpus luteum is present. The surface may be smooth in young women, show multiple rounded cystic structures, or show scarring and shrinking in older women.
The position of the ovary is subject to considerable variation. In the nullipara the ovary lies in the ovarian fossa, a depression in the pelvic wall below the external iliac vessels and in front of the ureter. A mesovarium attaches the ovary to the posterior wall of the broad ligament, while the posterior margin is free. The peritoneum does not cover the ovary proper, which is covered by germinal epithelium.
At either end the ovary is supported by ligaments. At the tubal pole the ovary is attached to the suspensory ligament, a fold of peritoneum which forms a mesentery for the ovary and contains the ovarian vessels. At the other pole is the utero-ovarian ligament.
The hilus is the base of the ovary; at this point the ovarian blood vessels enter. The ovarian arteries arise from the abdominal aorta just below the renal arteries. They pass downward across the pelvic brim, cross the external iliac artery, and traverse the infundibulopelvic fold of peritoneum. Branches go to the ureter, round ligament, and tube and anastomose with the uterine artery.
As the ovarian artery passes through the mesovarium, it separates into multiple branches that enter the ovarian hilus. Each of these arteries divides into two medullary branches which cross the ovary. Cortical branches arise from the medullary branches and supply the cortex and follicles. Two prominent veins enter the hilus and, in general, follow the arterial pattern.
At the hilus venous drainage forms a pampiniform plexus, which consolidates to form the ovarian vein. On the fight side the ovarian vein drains into the inferior vena cava, while the left ovarian vein drains into the left renal vein. The ovarian as well as the uterine blood supply frequently is anomalous.
The nerve supply4 derives from a sympathetic plexus accompanying the vessels of the in-fundibulopelvic ligaments. The plexus arises at the level of the tenth thoracic segment, but fibers from renal and aortic plexuses as well as from the mesenteric and celiac ganglia are present.
Hilus cells, which are nonencapsulated nests of large vacuolated cells, frequently are found in the hilus of the ovary. These cells are similar to the interstitial or Leydig cells of the testis.
Any discussion of the ovary should include those portions of the mesonephric (wolffian) tubules and duct that persist in the adult female as vestigial structures between the peritoneal layers of the broad ligament. The epoophoron lies in the mesosalpinx between the tube and the ovary. It usually consists of 8 to 20 small tubules which join a common duct at right angles. Ordinarily the longitudinal duct has blind ends, but it may be prolonged as Gartner's duct. Mesonephric duct vestiges known as Gartner's duct cysts may be found alongside the uterus, cervix, or vagina. Vestiges of the mesonephric tubules also may be present as clear pedunculated cysts below the fimbria of the tube.
Medial to the epoophoron lies the paroophoron, a rudimentary organ with a few scattered tubules. It likewise is of mesonephric origin. These mesonephric vestiges are of clinical importance, since they occasionally give rise to cysts which require surgical excision.
In the female embryo, primitive germ cells migrate from the epithelial lining of the hindgut and invade the subjacent layer of mesenchyma in the sexually undifferentiated gonad. These cells form radial cords and consist of primordial egg cells and cellular masses of prospective granulosa cells. As the fetus develops, the germinal cords become segregated into islands, each containing several germinal cells. At birth the full-term infant already has developing and degenerating follicles.
A primordial follicle consists of an oocyte with a layer of follicular cells surrounding it. When such a follicle is to undergo ovulation, marked changes occur in the egg and its follicular cells (Fig. 15). The ovum reaches its mature size as the antrum appears in the follicle. Concurrent with the growth of the oocyte, the granulosa cells proliferate and a multi-layered structure develops. An outer connective tissue sheath derived from the ovarian stroma is formed. This sheath is called the theca and subsequently divides into the theca externa and theca interna.
At first the developing follicle sinks deeper into the cortex, but as it increases in size it again returns to the surface. A theca cone develops, its axis pointing to the surface. At the same time the zona pellucida, a clear zone around the ovum, forms. An antrum or cell-free area containing follicular fluid develops. Surrounding the oocyte is a cluster of granulosa cells resembling a small mound, upon which the oocyte rests; this is called the cumulus oophorus (Fig. 16). As ovulation approaches, the follicle bulges and the wall thins. The basic mechanism which precipitates ovulation has not been determined; it is obviously hormone related.
Following rupture of the follicle and extrusion of the ovum, bleeding occurs at the rupture site and a blood clot forms. This is called the corpus hemorrhagicum. Granulosa cells grow into this clot, and the resulting mass of cells is known as the corpus luteum (Fig. 17).
Quite rarely there is total ovarian agenesis, or complete absence of ovarian tissue. Hypoplastic ovaries are more frequent; these usually are small and slender with ovarian stroma containing a few primordial follicles. Extremely rare is a supernumerary or third ovary located at some distance from the normally placed ovary and having no connection with the utero-ovarian, infundibulopelvic, or broad ligaments. More frequent is an accessory ovary, which is a small mass of ovarian tissue near the ovary or connected with it. Ovaries may be found in unusual places as a result of failure of descent during embryonic life. The clinical significance of structural variations in the adult ovary was studied by Boss and co-workers5.