GYN Atlas - High-Grade Squamous Intraepithelial Lesion


John M. Bauer, MD
It is not uncommon on the conventional Pap smear to find the small, abnormal cells associated with HSIL entrapped in mucus or “hiding” amongst groups of cells in background material. Samples processed with the ThinPrep System have an altered presentation because the mucus and debris are dispersed. At screening magnification, the small cells of HSIL “stand out” either singly or in small groups in the background of the cell deposit. These cells should alert you to focus more closely on the material present and to look for additional diagnostic groups of high-grade epithelial cells. Whenever these small single cells or groups are seen under low magnification, it is useful to “screen” a portion of the slides under high magnification. It is important to note that the dispersion step of the ThinPrep System process will not break up true epithelial groups, but rather due to the dyshesive nature of high-grade lesions, more single cells will be present; these are the “clue” cells to be on the lookout for.

The criteria for HSIL on the ThinPrep® Pap Test are as follows: The single, most important criterion for HSIL is the presence of asymmetrical 3-D nuclear structural abnormalities. This is a concept that must be clearly understood in order to master the interpretation of HSIL. There will be an abnormality to the structure of the dysplastic nucleus that can be thoroughly appreciated only by focusing up and down on the individual cell. This is the most difficult concept to demonstrate on the printed (two-dimensional page); but it is, nonetheless, the most important.

Imagine focusing up and down on a miniature cauliflower or closed fist or baseball mitt or tonsil. What would the surface of a raisin look like? A normal nucleus has a relatively round or ovoid shape and its surface is smooth. A dysplastic cell will have humps, bumps, corrugations, crevices, and strange protuberances. These very distinctive abnormalities are the essence of dysplasia, particularly HSIL. This is the very detail that is most often lost in conventional cytology due to the various artifacts of fixation and staining that limit the ability to interpret those conventional smears.

These 3-D nuclear structural abnormalities are to be distinguished from simple, “irregular nuclear outlines” which will often be present as a two-dimensional phenomenon in benign cells on the ThinPrep® Pap Tests. They are two-dimensional in that these “wrinkles” cannot, when the examiner focuses up and down, be traced into the center of the nucleus in the form of crevices, mountains, etc.; they can create deceptive “look-alikes” to the novice.

These 3-D structural abnormalities may not be present in every dysplastic cell on the slide, but they will be obvious in at least some cells somewhere on the slides. Obviously, the ability to see “into” the nucleus of a cell is going to be directly related to the quality of staining. (All ThinPrep® Pap Tests make visualizing cellular changes easier when compared to conventional Pap smears, but over staining or the slightest staleness of reagents will have a direct effect on this the most critical aspect of evaluation.) Also, these 3-D structural defects should be asymmetrical, as opposed to nuclear grooves or simple creases that involve the full breadth of the nucleus occasionally creating a difficult “look-alike”. The presence of these exaggerated nuclear 3-D abnormalities establishes the diagnosis of HSIL.