The opening to the uterus is called the cervix. It is located at the end of the vagina and can be seen during an examination with the use of a vaginal speculum.
The cervical skin is made of multiple layers of skin cells, called squamous epithelium.
The cells at the bottom of the epithelium sit on a basement membrane. This bottom-most layer of skin cells is called the basal layer. As these cells reproduce, they push their daughter cells upward toward the surface of the skin.
Rising through the skin layer, the cells mature, becoming flat and pancake-like (as opposed to round and plump). Their nuclei initially become larger and darker, then smaller.
Depending on the spatial orientation, these mature cells may have different appearances.
When they reach the surface, the cells are exfoliated into the vaginal cavity. By performing a Pap smear and examining the collected cells under the microscope, normal, fully mature skin cells are the expected result.
Sometimes, the basal layer reproduces cells faster than normal. The daughter cells are pushed upward at an accelerated rate, and they reach the skin surface before they have time to fully mature.
This process is called dysplasia, or abnormal growth.
There are degrees of dysplasia, mild, moderate and severe. None of this is cancer, but it is true that the next step beyond severe dysplasia is cancer of the cervix.
Dysplasia is not visible to the naked eye, and detection requires special testing procedures.
If you take a skin biopsy of mild dysplasia, you will find areas of slightly immature cells at the skin surface. With moderate dysplasia, the immaturity is more significant. With severe dysplasia, there is essentially no maturation of the cells from the bottom to the top. Pap smears done on patients with severe dysplasia usually show significant numbers of basal cells with no maturation at all.
After the immature cells extend throughout the full thickness of the cervical skin, they can then break through the basement layer and begin invading the underlying tissue. This is called invasive cancer.
Not everyone with dysplasia will advance to cancer if untreated. In fact, less than one in ten women with mild dysplasia will advance to moderate, then severe dysplasia and end up with cancer of the cervix. Most will remain stable at this level, or regress back to normal.
For moderate dysplasia, only about one in four will advance, untreated, to cancer. With severe dysplasia, about half will advance, untreated, to invasive cancer of the cervix.
These changes take time to occur. For those whose mild dysplasia is heading for cancer, it is frequently estimated to take an average of 10 years to reach cancer. Still, dysplasia should receive prompt attention.
Mild dysplasia is also known as CIN I, and low-grade SIL. It is most often associated with the presence of the Human Papilloma Virus.
Those with persistent mild dysplasia, particularly if there is high risk HPV virus present, will undergo further evaluation, frequently in the form of colposcopy. Colposcopy uses magnification and a special light filter to evaluate the cervix.
During colposcopy, the cervix is exposed to acetic acid, which enhances the physician’s ability to identify areas of abnormality. Biopsies are taken of the worst-looking area of abnormality, and treatment planned based on the outcome.
Mild dysplasia is frequently left untreated because the spontaneous regression rate is so high, the access to followup is usually good, and the rate of progression is so slow.
For moderate dysplasia and above (also known as high grade SIL, or CIN II or III), the abnormalities are commonly treated with removal or elimination of the abnormality. A number of tools can be used for this, including laser, freezing, or LEEP procedures. These minor surgical procedures are expected to eliminate the abnormal cells without disturbing future childbearing.