The category of Negative for Intraepithelial Lesion (NIL) simply indicates that the specimen contained adequate amount of cells and these cells showed no evidence of abnormality.
There are several types of cells examined for abnormalities. They are:
Other normal cells that are occasionally found on a pap smear:
The superficial cell comprises the outermost layer of the non-keratinizing epithelium. The 1604um eosinophillic polygonal shaped cell houses a 25 um centrally placed pyknotic nucleus. No nuclear detail can be seen due to nuclear degeneration. Superficial squamous cells are seen in abundance during the late proliferative and ovulatory phases of the menstrual cycle. At these points estrogen is at it's peak.
The polygonal shaped intermediate squamous cell is 1256-1618um. The cell is found in the startum spongiosum (midzone) layer of the squamous epithelium. The intermediate cell's cytoplasm is thin, transparent and typically stains basophillic. The centrally placed nucleus is 35um. the nucleus is vesicular with fine evenly dispersed granular chromatin. Intermediate squames are seen in abundance when the progesterone hormone is at high levels. This occurs during the luteal and the early follicular phases of the menstrual cycle and the second and third trimester of pregnancy.
Squamous Metaplastic Cells
Parabasal cells are found in the basal layer of the squamous epithelium. The round to oval shaped cell is 318-706 um in size. The dense homogenous basophillic cytoplasm encloses a 50um nucleus. The nuclear detail reveals a finely granular chromatin. Parabasals are an uncommon finding on pap smears of women with estrogen production or replacement hormone. Along with basal cells, these cells are seen in atrophic pap smears from patients that are pre-menstrual, postpartum, taking estrogen restricting hormones (ie. depo-provera) and women who are post-menopausal.
Basal Cells are found in the lower most layer of the squamous epithelium. These cells function to anchor the epithelium to the basement membrane and undergo mitosis for epithelial regeneration. These cells are seen on post menopausal (atrophic) pap smears but never seen on cyclic patients pap smear.
These cells are approximately 200 um with a cell diameter of about 10-12 um. The basal cell cytoplasm is homogenous and quite dense. Within the cytoplasm is a 50um centrally placed nucleus with fine granular chromatin. On occasion the nucleus can appear hyperchromatic from the increased nuclear activity.
The tall columnar shaped endocervical cells is 188um in size. The mucinous cytoplasm of endocervical cells can be granular or vacuolated. The 50um round basally placed nucleus reveals a fine granular chromatin with an occasional nucleoli. Endocervical cells can be seen on pap smears in three arrangement: single cells, as strips or as a sheet.