Anatomy of the Uterine Cervix and the Transformation Zone CHAPTER 1 CHAPTER
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CHAPTER 2 . CHAPTER 2 CHAPTER Anatomy of the uterine cervix and the transformation zone CHAPTER 1 CHAPTER The cervix is a fibromuscular the uterine arteries superiorly and meets the glandular epithelium at organ that links the uterine cavity to laterally. the squamocolumnar junction (SCJ). the vagina. Although it is described The cervix has several different The SCJ is dynamic and moves dur- as being cylindrical in shape, the an- linings. The endocervical canal is ing early adolescence and during a terior and posterior walls are more lined with glandular epithelium, and first pregnancy. The original SCJ often ordinarily apposed. The cer- the ectocervix is lined with squamous originates in the endocervical canal, vix is approximately 4 cm in length epithelium. The squamous epithelium but as the cervix everts during these and 3 cm in diameter. The cervix of a parous woman is considerably Fig. 2.1. Line drawing of normal female genital tract anatomy: sagittal sec- larger than that of a nulliparous tion. In this drawing, the uterus is anteverted. woman, and the cervix of a woman of reproductive age is considerably larger than that of a postmenopausal woman. The cervix occupies both Cervix Uterus an internal and an external position. Its lower half, or intravaginal part, Bladder Posterior fornix lies at the upper end of the vagina, Anterior Rectum and its upper half lies above the va- fornix Sacrum gina, in the pelvic/abdominal cavity Pubic bone (Fig. 2.1). The two parts are approx- Vagina imately equal in size. The cervix lies Urethra between the bladder anteriorly and the bowel posteriorly. Laterally, the ureters are in close proximity, as are Chapter 2. Anatomy of the uterine cervix and the transformation zone 13 times, the SCJ comes to lie on the the majority of cervical cancer and these procedures. Also, the cervix of ectocervix and becomes the new originates in the TZ. Glandular cer- a parous woman tends to have slight- SCJ. In colposcopy terminology, the vical cancer originates in either the ly less sensory appreciation, which SCJ is this new SCJ. The epithelium TZ or the glandular epithelium above may be due to damage to nerve end- between these two SCJs is the TZ the TZ. ings during childbirth. Because sym- or transition zone, and its position is pathetic and parasympathetic fibres also variable. It may be small or large 2.1 Tissue constituents of the are also abundant in the endocervix, and usually becomes more ectocer- cervix dilatation and/or curettage of the en- vical during a woman’s reproductive docervix may occasionally lead to a years, returning to an endocervical 2.1.1 Stroma vasovagal reaction. position after menopause. The cervix is covered by both When the uterus is anteverted, The stroma of the cervix is com- stratified, non-keratinizing squa- the cervix enters the vaginal vault posed of dense, fibromuscular tissue mous epithelium and columnar epi- through a slightly posterior approach, through which vascular, lymphatic, thelium. As mentioned above, these whereby at speculum examination and nerve supplies to the cervix pass two types of epithelium meet at the the cervical os is directed towards and form a complex plexus. SCJ. the posterior vaginal wall (Fig. 2.1). The arterial supply of the cervix When the speculum is opened, the is derived from the internal iliac arter- 2.1.2 Squamous epithelium cervix tends to be brought more cen- ies through the cervical and vaginal trally into view and into line with the branches of the uterine arteries. The Usually, most of the ectocervix and longitudinal axis of the vagina. Most cervical branches of the uterine ar- the entire length of the vagina is lined women have an anteverted uter- teries descend in the lateral aspects with squamous epithelium, which is us. When the uterus is retroverted, of the cervix at the 3 o’clock and uniform, stratified, and non-keratiniz- the cervix tends to enter the vagina 9 o’clock positions. The veins of the ing. Because mature squamous epi- slightly more anteriorly, and in this cervix run parallel to the arteries and thelium contains glycogen, it readily case the cervix may be more difficult drain into the hypogastric venous takes up Lugol’s iodine (and is there- to locate at first speculum exposure. plexus. The lymphatic vessels from fore Schiller test-negative). When When the speculum is positioned the cervix drain into the common ili- epithelium does not take up Lugol’s properly and opened, the cervix ac, external iliac, internal iliac, obtu- iodine, it is Schiller test-positive. Cer- tends to become positioned centrally rator, and parametrial nodes. vical squamous epithelium is smooth and in a plane perpendicular to the The nerve supply to the cervix is and looks slightly pink to the naked longitudinal axis of the vagina. derived from the hypogastric plex- eye in its non-pregnant state. During The external os of the cervix will us. The endocervix has extensive pregnancy it becomes progressively nearly always be visible to the naked sensory nerve endings, whereas more vascular and develops a bluish eye at speculum examination. The there are very few in the ectocervix. hue. visible external lining of the cervix Hence, procedures such as biopsy, The lowest level of cells in the derives from the vaginal (squamous) thermal coagulation, and cryother- squamous epithelium (Fig. 2.2) is a epithelium. The endocervical or apy are relatively well tolerated in single layer of round basal cells with glandular epithelium is not usually most women, although there is good large dark-staining nuclei and little visible to the naked eye at speculum evidence that local anaesthesia ef- cytoplasm, attached to the base- examination. At the upper end of the fectively prevents the discomfort of ment membrane. The basement endocervical canal, the endocervical epithelium becomes the endome- Fig. 2.2. Squamous epithelium of the vagina and ectocervix. trial lining of the uterine cavity. The lower half, or intravaginal part, of the Superficial cell layer cervix lies at the top of the vagina, Intermediate cell surrounded by the vaginal fornices. layer These are the lateral, anterior, and posterior fornices and are where Parabasal layer the vaginal epithelium sweeps into Stromal the cervix circumferentially. Squa- papilla Basal cell layer mous cervical cancer accounts for Basement membrane Stroma 14 membrane separates the epithelium visual examination, it appears pale, The columnar epithelium does from the underlying stroma. The sometimes with subepithelial pete- not form a flattened surface in the epithelial–stromal junction is usual- chial haemorrhagic spots, because it endocervical canal but is thrown ly straight. Sometimes it is slightly is easily prone to trauma. into multiple longitudinal folds pro- undulating, with short projections of truding into the lumen of the canal, stroma, which occur at regular inter- 2.1.3 Columnar epithelium giving rise to papillary projections. It vals. These stromal projections are forms several invaginations into the CHAPTER 2 CHAPTER called papillae, and the parts of the The endocervical canal is lined with substance of the cervical stroma, re- epithelium between the papillae are columnar epithelium (often referred sulting in the formation of endocer- called rete pegs. to as glandular epithelium). It is com- vical crypts (sometimes referred to The basal cells divide and mature posed of a single layer of tall cells as endocervical glands) (Fig. 2.4). to form the next few layers of cells, with dark-staining nuclei close to The crypts may traverse as far as called parabasal cells, which also the basement membrane (Fig. 2.3). 5–6 mm from the surface of the cer- have relatively large dark-staining Because of its single layer of cells, vix. This complex architecture, con- nuclei and greenish-blue basophilic it is much shorter in height than the sisting of mucosal folds and crypts, cytoplasm. Further differentiation stratified squamous epithelium of gives the columnar epithelium a and maturation of these cells leads the cervix. On visual examination, it grainy or grape-like appearance on to the intermediate layers of polyg- appears reddish, because the thin visual inspection. onal cells with abundant cytoplasm single-cell layer allows penetration A localized overgrowth of the en- and small, round nuclei. These cells of the stromal vascularity. At its dis- docervical columnar epithelium may form a basket-weave pattern. With tal or upper limit, it merges with the occasionally be visible as a reddish further maturation, the superficial endometrial epithelium in the lowest mass protruding through the exter- layers of large and markedly flat- part of the body of the uterus. At its nal os on visual examination of the tened cells with small, dense, pyk- proximal or lower limit, it meets with cervix. This is called a cervical polyp notic nuclei and transparent cyto- the squamous epithelium at the SCJ. (Figs. 2.5 and 2.6). It usually begins plasm are formed. Overall, from the It covers a variable extent of the ec- as a localized enlargement of a sin- basal layer to the superficial layer, tocervix, depending on the woman’s gle columnar papilla and appears as these cells undergo an increase in age and reproductive, hormonal, and a mass as it enlarges. It is composed size and a reduction in nuclear size. menopausal status. of a core of endocervical stroma The cells in the intermediate and superficial layers contain abundant Fig. 2.3. Columnar epithelium of the endocervical canal. glycogen in their cytoplasm, which stains mahogany brown or black after the application of Lugol’s iodine and Columnar cells magenta with periodic acid–Schiff stain in histological sections. Gly- cogenation of the intermediate and Stroma superficial layers is a sign of normal maturation and development of the squamous epithelium.