There are two different systems for classifying cervical dysplasia. There are some differences between them, although what they are describing is similar. Let's walk through them:
The Bethesda, or SIL (squamous intraepithelial lesion) System looks only at individual cells, generally from a Pap test, and classifies them according to the degree of cell abnormality. These break down into:
- ASCUS (atypical squamous cells of undetermined significance) means the cells aren't quite right, but they aren't clearly dysplastic, either. This can be caused by a lot of different factors, including hormonal changes, yeast or other infections, medications, or other sources of inflammation. HPV testing is sometimes done at this point
to help decide whether to wait and do another Pap in a few months or do further testing sooner.
- AGUS or AGCUS (atypical glandular cells of undetermined significance) is a finding of atypical glandular cells. This is less common, but since a different type of cancer (adenocarcinoma) develops from glandular (mainly the columnar) cells, this is usually followed up right away with more testing. Adenocarcinoma often doesn't have the extended precancerous phase that squamous cell carcinoma does.
- LSIL - low grade squamous intraepithelial lesion - this is also called "mild cervical dysplasia", however, the true degree and extent of the cervical dysplasia can only be determined upon further evaluation of the cervix itself. Since most LSIL "regresses" - that is, returns to normal without treatment, a woman with LSIL may be advised to return for another Pap test in a few months. Some physicians are more cautious and do more careful follow-up at this point, however.
- HSIL - high grade squamous intraepithelial lesion - this type of Pap result will always be evaluated further and treated, as it detects cell changes that have progressed beyond the mild stage.
CIN system - The other major system of classifying cervical dysplasia is called the CIN system, for cervical intraepithelial neoplasia. There are corresponding classifications for vaginal and vulvar dysplasia called VAIN and VIN. This system of classification is based both on the degree of ˙cervical dysplasia in the individual cells (like SIL) and how far below the surface ( epithelium
) of the cervix the dysplasia goes. To determine the level of CIN, a small piece of tissue is usually obtained via biopsy. Although it's not uncommon to see Pap tests interpreted in terms of CIN, in my observation there is a trends towards using the SIL system for the cellular changes found in a Pap test, and then using CIN to describe the depth of the dysplasia found in a biopsy.
- CIN I - corresponds to mild cervical dysplasia or LSIL. Additionally, the abnormal cells are only on the very surface of the cervix. As stated under SIL, most of these will regress back to normal over time. About 11% will progress to CIN 3. Only a very small percentage of CIN I leads to cancer.
- CIN 2 - corresponds to moderate cervical dysplasia or HSIL. About half of the thickness of the epithelium is abnormal (dysplastic). Left alone, about 43% of CIN 2 will regress back to normal, and 20% will progress to CIN 3.
- CIN 3 - corresponds to severe cervical dysplasia or HSIL. All or almost all of the epithelium is dysplastic. Although some CIN 3 will spontaneously regress, this is almost always treated since the next step is cancer. This is sometimes also referred to as carcinoma in situ
(CIS).
Cancer - by definition, when cervical dysplasia invades the basement membrane, which is the layer of cells under the epithelium, it has become malignant (cancerous).
Another term creeping more into Pap smear reports is koilocytotic, which refers to a type of cell change commonly caused by HPV. Koilocytotic changes are not cancerous or precancerous, but warrant monitoring. They are often accompanied by cervical dysplasia.
Info Source: Dysplasia 101
