Fig. 1.1
Transvaginal ultrasound of the ovary, showing the normal anatomy
The pelvic and urogenital diaphragms form the pelvic floor. The former is a funnel-shaped fibromuscular partition that creates the primary support structure for the pelvic organs. It comprises the anus levator muscles (pubococcygeus, puborectal, and iliococcygeal) and coccyx, together with its upper and lower fascia. The loss of normal tonus of the anus levator, by direct muscle denervation or injury, results in sagging of the urogenital gap that is involved in the beginning of prolapse in females.
The muscles of the urogenital diaphragm (deep transverse perineal muscle and urethral sphincter) reinforce the front of the pelvic diaphragm, and are protected by upper and lower fascia of the urogenital diaphragm-pubovesicocervical ligament.
The urogenital diaphragm is closely related to the vagina and urethra, and an injury to the diaphragm is associated with cystocele and urethrocele.
Vascularization and Lymphatic Drainage
The main arteries that irrigate the pelvic structures and the organs are shown in Fig. 1.2:
- (a)
Median sacral artery – a single vessel located on the mid-line, emerging from the posterior part of the terminal aorta. It supplies the bone and muscular structures of the posterior pelvic wall.
- (b)
Internal iliac arteries (hypogastric) – originate from the common iliac arteries (terminal division of the aorta at the level of the fourth lumbar vertebra). They move down close to the ureter, and branch out into further divisions consisting of the following arteries: superior gluteal, lateral sacral, iliolumbar, and its previous division consisting of the obturator artery, internal pudendal, umbilical, superior, media and inferior bladders, rectal media, uterine, and vaginal and inferior gluteal.
- (c)
Ovarian arteries – originate at the ventral surface of the aorta, just below the origin of the renal vessels. They cross near the common iliac vessels; in proximity to the ureter, it departs from its course, crossing over the ureter while running superficial to the psoas muscle, and then laterally to the ureter, where it enters the pelvis as part of the infundibulopelvic ligament. They supply with blood the ovaries, fallopian tubes, and broad ligament. If the hypogastric arteries, ovarian arteries, sacral or inferior mesenteric need suturing, direct branches of the aorta will supply blood to the pelvic structures once irrigated by the hypogastric arteries.
Fig. 1.2
Pelvic MRI, Sagittal TSE T2 weight, demonstrating the normal zonal anatomy of the uterus
The venous system accompanies the arteries, except for the ovarian arteries, in which the right one opens into the inferior vena cava, and the left into the left renal vein. Lymphatic drainage, however, is accomplished by lymph vessels that originate in the walls of the uterus, fallopian tubes, ovaries, and vagina, heading for the internal and external iliac, common iliac, aortic (para-aortic), and superior and profound inguinals. Among the most important lymph nodes, Cloquet’s (or Rosenmüller’s) can be mentioned; these are the highest of the deep inguinal lymph nodes, located at the opening of the femoral canal.
Innervation
The pelvis is innervated by both the autonomic and somatic nervous systems.
Somatic innervation is carried by the lumbosacral plexus, which provides motor and sensory innervation to the lower wall, the pelvic and urogenital diaphragms, the perineum and the hip, and the lower extremities. The responsible nerves are the iliohypogastric, ilioinguinal, side femoral cutaneous, femoral, genitofemoral, obturator,superior and inferior gluteus, posterior cutaneous of the thigh, sciatic, and pudendal.
Autonomic innervation, however, is accomplished by the following plexus:
- (a)
Aortic, located laterally to the spine;
- (b)
Ovarian, responsible for the innervation of the ovaries, fallopian tubes and part of the broad ligament;
- (c)
Inferior mesenteric, which innervates the left colon, the sigmoid and rectum;
- (d)
Superior hypogastric or pre-sacral plexus is responsible for pelvic innervation. It is the continuation of the aortic plexus, under the peritoneum in front of the terminal aorta, the fifth lumbar vertebra and the promontory, medial to the ureters. Just below the promontory, the superior hypogastric plexus is divided into two loosely arranged nerve trunks, the hypogastric nevi. These nerves course below and laterally, to connect themselves to the inferior hypogastric plexus, a dense network of nerves and ganglia that are situated at the side wall of the pelvis, superposing the internal iliac vessels.
The inferior hypogastric plexus includes efferent, afferent (sensory), and parasympathetic fibers that emerge from the splanchnic pelvic nerves. It is divided into the bladder plexus, middle rectal plexus, and uterovaginal plexus.
Internal Genitalia
Ovary
The ovaries are a pair of gonadal structures that are suspended between the pelvic wall and the uterus by the infundibulopelvic ligament, laterally, and by the utero-ovarian ligament, medially. At the bottom, the hilar surface connects to the broad ligament by its mesentery, in a dorsal position to meso fallopian tubes and the uterine tube. Primary neurovascular structures – the ovarian arteries that supply the ovaries – reach the ovary through the infundibulopelvic ligament. The size of the ovaries are approximately 3–4 cm long, 2 cm wide, and 1 cm thick; they weigh 3–9 g.
Each ovary consists of a cortex and a medulla, and is covered by a single layer of cuboidal epithelium. The cortex consists of specialized stroma and follicles in various stages of development or regression. The medulla is located in the hilar portion and consists of fibromuscular tissue and blood vessels (Fig. 1.1).
Uterine Tubes
The uterine tubes are hollow, paired structures located in the mesofallopian tubes. They range from 7 to 12 cm in length and are about 1 cm in diameter [3]. They are divided into four parts: infundibular – terminal where the fimbriae approach the ovarian surface, aiding in the capture of gametes; ampullary – longest portion, with a more tapered diameter, and greater lateral walls; isthmic – shorter, and with thicker walls, closer to the uterine wall; and interstitial, which lies within the uterine wall, and forms the tubal ostia in the endometrial cavity (Fig. 1.3).
Uterus
The uterus is a mobile, muscular, pear-shaped organ located between the rectum and the bladder. It is attached to the pelvic sidewall in its supracervical portion, to the cardinal ligaments (Mackenrodt) and, in its rear section, held by uterosacral ligaments. Its most common position is anteversoflexion, but it can also be in an intermediate or retroversoflected position. The uterus is divided into the following regions: fundus – above the tubal ostia; uterine cornu – bottleneck, which receives the insertion of the tubes; body; isthmus – where the endocervical canal opens in the endometrial cavity; and the cervix – the portion located in the vagina, approximately 3 cm in length, consisting of a few muscle fibers, but large amounts of connective tissue.
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