CHAPTER 1 Surgical anatomy
Introduction
A clear understanding of the anatomy of the female pelvis is essential to successful gynaecological surgery and the avoidance of surgical morbidity. The close relationships between the reproductive, urinary and gastrointestinal tracts must be appreciated, together with the pelvic musculofascial support, vascular and lymphatic circulations, and neurological innervation. It is important to understand the effect of pneumoperitoneum on the anatomy and relationships of the pelvis, and the opportunities afforded by a retroperitoneal approach in minimal access techniques. Figure 1.1 shows a panoramic view of the pelvis from the umbilicus during a laparoscopy. The probe is lifting the right ovary, displaying the right pelvic side wall and ureter (arrows).
The Ovary
The size and appearance of the ovaries depend on both age and the stage of the menstrual cycle. In the young adult, they are almond shaped, solid and white in colour, 3 cm long, 1.5 cm wide and approximately 1 cm thick. The long axis is normally vertical before childbirth; after this, there is a wide range of variation, presumably due to considerable displacement in the first pregnancy.
The ovary is the only intra-abdominal structure not to be covered by peritoneum. Each ovary is attached to the cornu of the uterus by the ovarian ligament, and at the hilum to the broad ligament by the mesovarium, which contains its supply of vessels and nerves. Laterally, each is attached to the suspensory ligament of the ovary with folds of peritoneum which become continuous with that over the psoas major.
Structure
The ovary has a central vascular medulla, consisting of loose connective tissue containing many elastin fibres and non-striated muscle cells, and an outer thicker cortex, denser than the medulla and consisting of networks of reticular fibres and fusiform cells, although there is no clear-cut demarcation between the two. The surface of the ovary is covered by a single layer of cuboidal cells, the germinal epithelium. Beneath this is an ill-defined layer of condensed connective tissue, the tunica albuginea, which increases in density with age. At birth, numerous primordial follicles are found, mainly in the cortex but some in the medulla. With puberty, some form each month into Graafian follicles which, at later stages of their development, form corpora lutea and ultimately atretic follicles, the corpora albicantes (Figure 1.2).
Relations
Anteriorly lie the fallopian tubes, the superior portion of the bladder and the uterovesical pouch; posteriorly is the pouch of Douglas. The broad ligament and its content are related inferiorly, whilst superior to the ovaries are the bowel and the omentum. The lateral surface of the ovary is in contact with the parietal peritoneum and the pelvic side walls.
Vestigial structures
The vestigial remains of the mesonephric duct and tubules are always present in young children, but are variable structures in adults. The epoophoron, a series of parallel blind tubules, lies in the part of the broad ligament between the mesovarium and the fallopian tube, the mesosalpinx. The tubules run to the rudimentary duct of the epoophoron, which runs parallel to the lateral fallopian tube. A few rudimentary tubules, the paroophoron, are occasionally seen in the broad ligament, between the epoophoron and the uterus.
In a few individuals, the caudal part of the mesonephric duct is well developed, running alongside the uterus to the internal os. This is the duct of Gartner.
Age-related changes
During early fetal life, the ovaries are situated in the lumbar region near the kidneys. They gradually descend into the lesser pelvis and, during childhood, they are small and situated near the pelvic brim. They are packed with primordial follicles. The ovary grows in size until puberty by an increase in the stroma. Ova are first shed around the time of onset of menstruation, and ovulation is usually established within a couple of years.
After the menopause, the ovary atrophies and assumes a smaller, shrivelled appearance. The fully involuted ovary of old age contains practically no germinal elements.
Blood supply
The main vascular supply to the ovaries is the ovarian artery, which arises from the anterolateral aspect of the aorta just below the origin of the renal arteries. The right artery crosses the anterior surface of the vena cava, the lower part of the abdominal ureter and then, lateral to the ureter, enters the pelvis via the infundibulopelvic ligament. The left artery crosses the ureter almost immediately after its origin and then travels lateral to it, crossing the bifurcation of the common iliac artery at the pelvic brim to enter the infundibulopelvic ligament. Both arteries then divide to send branches to the ovaries through the mesovarium. Small branches pass to the ureter and the fallopian tube, and one branch passes to the cornu of the uterus where it freely anastomoses with branches of the uterine artery to produce a continuous arterial arch (see Figure 1.3).
Figure 1.3 Posterosuperior aspect of the uterus and the broad ligament as seen from the umbilicus at laparoscopy.
The ovarian and uterine trunks drain into a pampiniform plexus of veins in the broad ligament near the mesovarium, which can occasionally become varicose. The right ovarian vein drains into the inferior vena cava, the left usually into the left renal vein.
The Fallopian Tube
The uterine or fallopian tubes are two oviducts originating at the cornu of the uterus which travel a rather tortuous course along the upper margins of the broad ligament. They are approximately 10 cm in length and end in the peritoneal cavity close to the ovary. This abdominal opening is situated at the end of a trumpet-shaped lateral portion of tube, the infundibulum. This opening is fringed by a number of petal-like processes, the fimbriae, which closely embrace the tubal end of the ovary. This fimbriated end has an important role in fertility.
Medial to the infundibulum is the ampulla which is thin walled and tortuous, and comprises at least half of the length of the tube. The medial third of the tube, the isthmus, is relatively straight. The tube has narrowed at this point, from approximately 3 mm at the abdominal opening to 1–2 mm. The final centimetre, the interstitial portion, is within the uterine wall.
Structure
The tubes are typical of many hollow viscera in that they contain three layers. The outer serosal layer consists of peritoneum and underlying areolar tissue. This covers the whole tube apart from the fimbriae at one end and the interstitial portion at the other. The middle muscular layer consists of outer longitudinal fibres and inner circular fibres. This is fairly thick at the isthmus and thins at the ampulla.
The mucous membrane is thrown into a series of plicae or folds, especially at the infundibular end. It is lined with columnar epithelium, much of which contains cilia which, together with the peristaltic action of the tube, help in sperm and ovum transport. Secretory cells are also present, as well as a third group of intercalary cells of uncertain function.
Relations
These are similar to those of the ovary (see above). Medially, the fallopian tube, after arching over the ovary, curves around its tubal extremity and passes down its free border.
The Uterus
The uterus is shaped like an inverted pear, tapering inferiorly to the cervix and, in the non-pregnant state, is situated entirely within the lesser pelvis. It is hollow and has thick muscular walls. Its maximal external dimensions are approximately 9 cm long, 6 cm wide and 4 cm thick. The upper expanded part of the uterus is termed the ‘body’ or ‘corpus’. The area of insertion of each fallopian tube is termed the ‘cornu’ and that part of the body above the cornu, the ‘fundus’. The uterus tapers to a small central constricted area, the isthmus, and below this is the cervix, which projects obliquely into the vagina and can be divided into vaginal and supravaginal portions (Figure 1.4).
The cavity of the uterus has the shape of an inverted triangle when sectioned coronally; the fallopian tubes open at the upper lateral angles (Figure 1.5). The lumen is apposed anteroposteriorly. The constriction at the isthmus where the corpus joins the cervix is the anatomical internal os.
Figure 1.5 Sectional diagram showing the interior divisions of the uterus and its continuity with the vagina.
Structure
The uterus consists of three layers: the outer serous layer (peritoneum), the middle muscular layer (myometrium) and the inner mucous layer (endometrium).
The peritoneum covers the body of the uterus and, posteriorly, the supravaginal portion of the cervix. This serous coat is initimately attached to a subserous fibrous layer, except laterally where it spreads out to form the leaves of the broad ligament.
The muscular myometrium forms the main bulk of the uterus and comprises interlacing smooth muscle fibres intermingling with areolar tissue, blood vessels, nerves and lymphatics. Externally, these are mostly longitudinal but the larger intermediate layer has interlacing longitudinal, oblique and transverse fibres. Internally, they are mainly longitudinal and circular.
The endometrium forms the inner layer and is not sharply separated from the myometrium: the tubular glands dip into the innermost muscle fibres. A single layer of columnar epithelium covers the endometrium. Ciliated prior to puberty, this columnar epithelium is mainly lost due to the effects of pregnancy and menstruation. The endometrium undergoes cyclical histological changes during menstruation and varies in thickness between 1 and 5 mm.
The cervix
The cervix is cylindrical in shape, narrower than the body of the uterus and approximately 2.5 cm in length. It can be divided into the upper, supravaginal and lower vaginal portions. Due to anteflexion or retroflexion, the long axis of the cervix is rarely the same as the long axis of the body. Anterior and lateral to the supravaginal portion is cellular connective tissue, the parametrium. The posterior aspect is covered by the peritoneum of the pouch of Douglas. The ureter runs approximately 1 cm laterally to the supravaginal cervix. The vaginal portion projects into the vagina to form the fornices.
The upper part of the cervix mainly consists of involuntary muscle, whereas the lower part is mainly fibrous connective tissue.
The mucous membrane of the endocervix has anterior and posterior columns from which folds radiate out, the arbor vitae. It has numerous deep glandular follicles which secrete a clear alkaline mucus, the main component of physiological vaginal discharge. The epithelium of the endocervix is cylindrical and also ciliated in its upper two-thirds, and changes to stratified squamous epithelium around the region of the external os. This change may be abrupt or there may be a transitional zone up to 1 cm in width.
Position
The longitudinal axis of the uterus is approximately at right angles to the vagina and normally tilts forwards; this is termed ‘anteversion’. The uterus is usually also flexed forwards on itself at the isthmus; this is termed ‘anteflexion’. In approximately 20% of women, this tilt is not forwards but backwards, termed ‘retroversion’ or ‘retroflexion’. In most cases, this does not have pathological significance and the uterus is mobile.
Relations
Anteriorly, the uterus is related to the bladder and is separated from it by the uterovesical pouch of peritoneum. Posteriorly is the pouch of Douglas plus coils of small intestine, sigmoid colon and upper rectum. Laterally, the relations are the broad ligament and that contained within it. Of special importance are the uterine artery and the ureter, running close to the supravaginal cervix.
Age-related changes
The disappearance of maternal oestrogenic stimulation after birth causes the uterus to decrease in length by approximately one-third and in weight by approximately one-half. The cervix is then around twice the length of the body of the uterus. At puberty, however, the corpus grows much faster and the size ratio reverses; the body becomes twice the length of the cervix. After the menopause, the uterus undergoes atrophy, the mucosa becomes very thin, the glands almost disappear and the walls become less muscular. These changes affect the cervix more than the corpus, so the cervical lips disappear and the external os becomes more or less flush with the vault.
The Vagina
The vagina is a fibromuscular tube which extends posterosuperiorly from the vestibule to the uterine cervix. It is longer in its posterior wall (approximately 9 cm) than anteriorly (approximately 7.5 cm). The vaginal walls are normally in contact, except superiorly, at the vault, where they are separated by the cervix. The vault of the vagina is divided into four fornices: posterior, anterior and two lateral. These increase in depth posteriorly. The mid-vagina is a transverse slit and the lower portion has an H-shape in transverse section.
Structure
The skin of the vagina is firmly attached to the underlying muscle and consists of stratified squamous epithelium. There are no epithelial glands present and the vagina is lubricated by mucus secretion from the cervix and Bartholin’s glands. The epithelium is thick and rich in glycogen, which increases in the postovulatory phase of the cycle. Doderlein’s bacillus is a normal commensal of the vagina, breaking down the glycogen to form lactic acid and producing a pH of approximately 4.5. This pH has a protective role for the vagina in decreasing the incidence of pyogenic infection.
The muscle layers consist of an outer longitudinal and inner circular layer, but these are not distinctly separate and are mostly spirally arranged and interspersed with elastic fibres.
The hymen
The hymen is a thin fold of mucous membrane across the entrance to the vagina. It has no known function. There are usually one or more openings in it to allow menses to escape. If these are not present, a haematocolpos will form with the commencement of menstruation. The hymen is usually, but not always, torn with first intercourse but can also be torn digitally or with tampons. It is certainly destroyed in childbirth and only small tags, carunculae myrtiformes, remain.
Relations
The upper posterior vaginal wall forms the anterior peritoneal reflection of the pouch of Douglas. The middle third is separated from the rectum by pelvic fascia and the lower third abuts the perineal body.
Anteriorly, the upper vagina is in direct contact with the base of the bladder, whilst the urethra runs down the lower half in the midline to open into the vestibule; its muscles fuse with the anterior vaginal wall.
Laterally, at the fornices, the vagina is related to the attachment of the cardinal ligaments. Below this are the levator ani muscles and the ischiorectal fossa. Near the vaginal orifice, the lateral relations include the vestibular bulb, bulbospongiosus muscle and Bartholin’s gland.
Age-related changes
Immediately after birth, the vagina is under the influence of maternal oestrogen so the epithelium is well developed. Acidity is similar to that of an adult and Doderlein’s bacilli are present. After a couple of weeks, the effects of maternal oestrogen disappear, the pH rises to 7 and the epithelium atrophies.
At puberty, the reverse occurs. The pH becomes acid again, the epithelium undergoes oestrogenization and the number of Doderlain’s bacilli increases markedly. The vagina undergoes stretching during coitus, and especially childbirth, and the rugae tend to disappear.
At the menopause, the vagina tends to shrink and the epithelium atrophies.
The Vulva
The female external genitalia, commonly referred to as the ‘vulva’, include the mons pubis, the labia majora and minora, the vestibule, the clitoris and the greater vestibular glands (Figure 1.6).
Labia majora
The labia majora are two prominent folds of skin with underlying adipose tissue bounding either side of the vaginal opening. They contain numerous sweat and sebaceous glands, and correspond to the scrotum of the male. Anteriorly, they fuse together over the symphysis pubis to form a deposition of fat, the mons pubis. Posteriorly, they merge with the perineum. From puberty onwards, the lateral aspects of the labia majora and the mons pubis are covered with coarse hair. The inner aspects are smooth but have numerous sebaceous follicles.
Labia minora
The labia minora are two small vascular folds of skin, containing sebaceous glands but devoid of adipose tissue, which lie within the labia majora. Anteriorly, they divide into two to form the prepuce and frenulum of the clitoris. Posteriorly, they fuse to form a fold of skin termed the ‘fourchette’. They are not well developed before puberty, and atrophy after the menopause. Their vascularity allows them to become turgid during sexual excitement.
Clitoris
This is a small erectile structure, approximately 2.5 cm long, homologous with the penis but not containing the urethra. The body of the clitoris contains two crura, the corpora cavernosa, which are attached to the inferior border of the pubic rami. The clitoris is covered by ischiocavernosus muscle, whilst bulbospongiosus muscle inserts into its root. The clitoris has a highly developed cutaneous nerve supply and is the most sensitive organ during sexual arousal.
Vestibule
The vestibule is the cleft between the labia minora. The vagina, urethra, paraurethral (Skene’s) duct and ducts of the greater vestibular (Bartholin’s) glands open into the vestibule (see Figure 1.7). The vestibular bulbs are two masses of erectile tissue on either side of the vaginal opening, and contain a rich plexus of veins within bulbospongiosus muscle. Bartholin’s glands, each about the size of a small pea, lie at the base of each bulb and open via a 2 cm duct into the vestibule between the hymen and the labia minora. These glands secrete mucus, producing copious amounts during intercourse to act as a lubricant. They are compressed by contraction of the bulbospongiosus muscle.
Perineal body
This is a fibromuscular mass occupying the area between the vagina and the anal canal. It supports the lower part of the vagina and is of variable length. It is frequently torn during childbirth.
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