Cervical cancer is the cause of 5% of female deaths worldwide.
Cervical cytology, or cervicovaginal cytology, has been the main test to prevent and detect cervical cancer. It studies the exfoliated cells of the squamocolumnar junction of the cervix.
Besides the detection of premalignant and malignant lesions, cervical cytology provides information on the hormonal state of the woman, as well as the presence of pathogenic microorganisms. Because of the susceptibility to carcinogenic viruses infections (e.g. the human papilloma virus – HPV), as well as for it’s anatomical location, vaginal cytology acts as a “sentinel” for the early detection of lesions and carcinomas.
Been the infection one of the most frequent clinical symptoms and one of the main causes that leads women to a gynecologist, screening programs are of vital importance in cervical cancer detection, since in its early stage this type of tumor does not manifest symptoms / signs.
Cervical cytology tests may be carried out on glass slides (conventional cytology) or through the well known liquid based cytology method.
Samples of conventional cytology are extracted using a spatula or “brush” to obtain uterine cervix cells so that they can be spread on a slide, fixed and subsequently observed on microscope.
In a liquid based cytology, the sample is transferred to a liquid (fixative), to better preserve the cells, DNA, RNA and proteins. The sample is then processed with the aim of the cells to become arranged into a thin layer without artifacts and without overlapping.
Features of normal cervical cells
Cells of the cervical cytology smears consist of squamous epithelial cells and glandular epithelial cells.
Superficial, intermediate, navicular, parabasal and basal cells are part of the squamous epithelial cells ( Figure C1 ).
Endocervical and endometrial cells are part of the glandular epithelial cells .
Squamous epithelial cells
Superficial cells appear in various conditions, including at the 1st phase of the cycle (pre-ovulation), after estrogen therapy or as a result of an ovarian tumor. Superficial cells are cells from the cervix superficial layer; they are polyhedral, with approximately 40 to 60 microns, have a wide cytoplasm, are homogeneous, translucent, eosinophil and sometimes with querato-hyaline granules. The nucleus of superficial cells is central, picnotic, round to oval, with no obvious chromatin, with regular nuclear membrane.
Intermediate cells usually appear at the 2nd phase of the cycle (after ovulation), in pregnancy, menopause and progesterone therapy. These are middle layer cells with abundant glycogen and may appear isolated (physiological exfoliation) or grouped (traumatic exfoliation). They have wide, translucent cytoplasm and sometimes eosinophil (with papanicolaou staining). Have wound edges with keratohyalin granules or vacuoles. The nucleus may be round or oval, larger than the superficial cells with clearly defined chromatin.
Navicular cells are less mature cells and therefore smaller than the intermediate. They appear frequently in pregnant women and may appear in pathological situations, like lutein and luteoma ovarian cysts. Navicular cells have a shape similar to a boat. They possess a glycogen rich cytoplasm which contributes to a densification of the cytoplasm along the cytoplasmic membrane.
In the deep layer of the epithelium are the parabasal cells. Parabasal cells are smaller than the navicular, with larger nucleus. They are round and regular with 15 to 20 microns. These cells have an augmented nucleus / cytoplasm ratio, their cytoplasm is dense, acidophilus, with well-defined cytoplasmic membrane and vacuoles. The nucleus is central, the chromatin is thin and uniform with granular distribution. They can be found in pre-puberty, postpartum, post-menopause, post-irradiation or by estrogen deficiency.
Basal cells are originated in the basal layer of the epithelium. They are rarely observed unless there is a traumatic exfoliation (erosion or ulceration of the mucosa), severe atrophy or infection. They are small cells with 15 microns, oval or round with a high nucleus / cytoplasm ratio.
Glandular epithelial cells
Endocervical cells are elongated or rounded cylindrical cells depending on the angle that are observed. They can appear in clusters of cells and show an aspect of honeycomb or palisade.
During the menstrual cycle, endocervical glands undergo cyclic changes in the secretory activity. In the proliferative phase, increasing levels of estrogen promote secretion of a thin, watery mucus, which allows the passage of sperm into the uterus at the time of ovulation. At this time the nucleus acquires an elliptical or spherical shape with a diameter of 7um.
After ovulation (secretory phase), the cervical mucus becomes highly viscous, forming a buffer that prevents the entry of microorganisms (and sperm) to the vagina. This is particularly important if pregnancy occurs. During this phase, the cytoplasm is clear and swollen. Abundant mucus moves the nucleus to the base of the cell.
Endometrial cells can be seen in smears until the 12th day of the menstrual cycle and slough off in the menstrual phase. Endometrial cells are smaller than the endocervical cells and their cytoplasm undergoes cyclic changes in response to hormones during the menstrual cycle. Endometrial cells can appear alone or in clusters as groups of cells arranged three-dimensionally, with barely visible details in the center. The nucleus of endometrial cells is round, hyperchromatic, often overlapping, with degenerated or scant cytoplasm.
In menstrual phase, endometrial cells appear in several degrees of conservation. Smears can be hemorrhagic with a dirty background and abundant cellular debris. Some groups of these cells are accompanied by histiocytes and leukocytes, which Papanicolaou called “exodus”.