Urogenital disorders

II./1.3.: Uterus (womb)

A pear-shaped muscular organ of 7-8 cm length, the uterus is flattened ventro-dorsally (from top to bottom, in an upright standing position), with a narrow cavity. The upper two-third, widening toward the tubal orifices in the shape of a triangle, is termed the body of uterus (corpus uteri), whereas the lower, narrow and cylindrical third part is the cervix uteri. In mature, nulliparous females the average lengths of the corpus and the cervix are 45 mm and 25 mm, respectively. In those women who have borne a child, the size of uterus post partum is somewhat larger 55 mm (corpus), and 25 mm (cervix). The convex part above the tubal orifices is termed fundus uteri. The isthmus uteri is a a narrow portion at the border between the corpus and the cervix, which is invisible from outside. The cervix protrudes downwards into the vagina. This is the portio vaginalis cervicis, a domed structure visible from the vagina, with the external cervical os (ostium uteri externum) in its center.The portio is surrounded by the vaginal wall to form the fornices.

Due to a deflection of the vaginal axis with respect to that of the cervix, the anterior fornix (fornix vaginae anterior) is shallower than the posterior fornix (fornix vaginae posterior). The other part of the cervix, lying above the vagina, is termed portio supravaginalis cervicis. The cavity of the cervix is called cervical canal (canalis cervicis), whereas that of the corpus uteri, triangular in a frontal section, is the cavum uteri proprium. The oviducts open from the paired upper angular recesses of the uterine cavity, whose superior border is slightly invaginated in a concave line connecting the tubal orifices. The lower angular evagination of the uterine cavity continues in the cervical canal, starting as the so called internal orifice and the isthmus. The middle part of the cervical canal has a fusiform swelling, in which the mucosa is thrown up in transverse folds resembling of palm leaves (plicae palmatae). The cervical canal terminates at the portio vaginalis as the external os (ostium uteri). This opening is round in nulliparous women, whereas in multiparous individuals it is a transverse slit with an irregular edge.

The uterus is situated in the lesser pelvis between the rectum and the urinary bladder, above the vagina. In a standing position, the vagina is tilted backwards at an angle of 30-40 degrees with respect to the vertical plane. The cervix forms a ventrally open angle of ca. 70 degrees with the longitudinal axis of the vagina. Such deflection is termed uterine anteversion (anteversio uteri), which, in fact, represents an overall forward tilt of 30-40 degrees. In addition, the axis of the uterus itself is broken at the isthmic region, whereby the axis of the cervix forms a forward directed angle of about 70 degrees with the axis of the corpus. The latter deflection is termed uterine anteflexion (anteflexio uteri). As a result, the body of the uterus lies in a near-horizontal position on the top of the bladder, depending on the state of distension of the latter. With a full bladder it is lifted up, whilst in case of an empty bladder it is bent more to the front. The flattened underside of the uterus is related to the urinary bladder, whereas its longer and more convex dorsal side is related to the coils of small intestine or, sometimes, of the sigmoid colon. Dorsally, the cervix touches the anterior surface of the rectum.

The uterus protrudes into the lesser pelvis from below. Its anterior and posterior surfaces are covered by peritoneum (perimetrium). These peritoneal coverings are fused along the edges of the uterus to form the broad ligament (ligamentum latum uteri), anchoring on the lateral side of pelvis. Given the forward tilted position of the uterus, the actual plane of the broad ligament is near-horizontal. In its anterior free edge, it accomodates the oviduct (Fallopian tube), moreover, its upward directed lamina forms a secondary duplicature for the ovary at about one finger's breadth behind the oviduct. The part of the broad ligament falling between the origin of the mesovarium an the Fallopian tube is designated as the mesosalpinx, whereas that part extending from the stem of mesovarium to the cervix is termed mesometrium. At the level of the cervix, the two plates of the broad ligament get separated; the anterior plate covering the paracystium beside the bladder,while the posterior plate covering the paraproctium beside the rectum.

Tightly adherent to the muscular wall of the uterus, the perimetrium leaves the antero-inferior surface of the uterus at the corpus-cervix border, and it passes on to the superior surface of the bladder. This transition is termed the vesico-uterine pouch (excavatio vesicouterina). The perimetrium extends further down the postero-dorsal surface of the uterus than on its anterior surface. It continues as far as the the portio supravaginalis, after which it passes on to the abdominal side of the posterior fornix and then on to the anterior part of the rectum. The latter transition site is considered the lowest point of the abdominal cavity in a standing individual: the recto-uterine pouch (excavatio rectouterina), a.k.a. the pouch of Douglas. (Notably, in a patient lying on his back, the lowest point is the pouch of Morison, or hepatorenal recess, situated in the upper part of the abdomen behind the liver). The pouch of Douglas usually contains low ileal coils. Its lateral border is the recto-uterine fold (plica rectouterina), a dorsally and superiorly directed peritoneal fold connecting the supravaginal part of the cervix to the rectum. The fold contains ligamentous connective tissue intermingled with smooth muscle, and it extends as far as the sacrum.

The round ligament (ligamentum teres uteri) raises a fold on the antero-inferior surface of the broad ligament. It starts from the area in front of the uterus-oviduct transition and extends as far as the internal opening of the inguinal canal (deep inguinal ring), and, having passed through this canal, it blends into the connective tissue of the labia majora. From the area behind the uterus-oviduct transition, i.e. on the superior-dorsal side of the broad ligament, the proper ovarian ligament (ligamentum ovarii proprium) passes to the ovary, corresponding to the upper free edge of the mesovarium between the uterus and the ovary. The latter ligaments play no role in the fixation of the uterus, these are mere remnants of gonadal development.

The serous membranes of ligamentum latum uteri are divided at the cervix into two folds, covering the subperitoneal region beside the bladder in front, and that beside the rectum in the back, respectively. The connective tissue situated between the two diverging peritoneal layers beside the cervix is termed parametrium. This represents a relatively loose space, within which connective tissue fibers pass to anchor the cervix to the lateral side of the pelvis. Views are divided whether or not this structure should be considered also as a separate horizontal plate (ligamentum cardinale uteri). The cervix is also attached to the bladder in front, and, indirectly, through the pubovesical ligament (ligamentum pubovesicale), to the symphysis, as well as, in the back, to the lower end of sacrum through the ligamentum rectouterinum. Position of the uterus is also maintained by the muscular tone of the pelvic floor (pelvic diaphragm and urogenital diaphragm). The urogenital diaphragm is tightly attached to the wall of the vagina, and, by so doing, it also provides support to the cervix. Also, the fascia covering the pelvic diaphragm is connected to the parametrium.

Blood supply of the uterus comes from the uterine artery, a branch of internal iliac artery. The uterine artery passes first on the lateral side of pelvis in a ventral direction, and then, following a medial turn on the pelvic floor, it reaches the cervix (isthmic region) along the lower border of the broad ligament. The artery has a prominent crossing with the ureter, in which the latter crosses the former from behind and from below. After this crossing, the ureter passes beside the cervix (related to the lateral fornix of vagina) in a ventral and medial direction to the base of the bladder. Having attained the uterine wall, the uterine artery divides into ascending and descending branches. The stronger ascending branch is tortuous, and it passes upward along the attachment line of the broad ligament before branching further into ovarian and tubal branches. The latter form anastomotic arcades with similar branches of the ovarian artery. The weaker descending branch of the uterine artery (vaginal ramus) passes beside the supravaginal part of the cervix, arching around the lateral fornices and down the lateral wall of the vagina.

Venous drainage of the uterus is maintained by valveless plexuses typical of the pelvic organs. Of the plexus venosus uterinus, plexus venosus cervicalis, plexus venosus vaginalis the plexus around the cervix is particularly robust. There is a profuse system of anastomoses inside the broad ligament with the venous plexuses of the oviduct and the ovary, all returning blood via the ovarian vein. Main venous drainage in the parametrial tissue along the inferior border of the broad ligament is directed toward the internal iliac vein. The plexus venosus vaginalis passes along the vagina as far as the urogenital diaphragm, before anastomosing with the system of internal pudendal vein. Notably, the middle zone of the uterus is relatively impoverished in blood vessels, enabling surgical intervention without the risk of major bleeding.

Lymphatic drainage of the endometrium is directed toward the parametrial lymphatic passages via the myometrium. Lymph from the perimetrium is also returned this way. Regional lymph nodes of the cervix are the nodi lymphaciti iliaci interni and nodi lymphatici sacrales. The region of the body of uterus is connected via the ovarian vessels to the para-aortic nodi lymphatici lumbales, as primary nodes. Upper part of the corpus and fundus is connected, through the agency of ligamentum teres, to the nodi lymphatici inguinales superficiales.

The sympathetic fibers of the uterus arise from the ganglion mesentericum inferius (plexus uterovaginalis). Parasympathetic innervation is provided by the plexus hypogastricus inferior.