GYN Atlas - Low-Grade Squamous Intraepithelial Lesion
SQUAMOUS CELLS
LOW-GRADE SQUAMOUS INTRAEPITHELIAL LESION (LSIL)
Diane D. Davey, MD
Squamous dysplasia is characterized by the presence of at least some squamous features in the cytoplasm of the abnormal cells. (Suggested Reading 1) The grade of dysplasia mirrors the maturity of the cells involved. For example, cells of mild dysplasia resemble mature metaplastic, superficial and intermediate cells while more severely dysplastic epithelium reflects less mature normal epithelium such as parabasal and/or immature metaplastic type cells. With the emergence of “The Bethesda System for Classification of Cervical Vaginal Diagnoses” the use of the term “dysplasia” lessened in favor of low-grade squamous intraepithelial lesions (LSIL) or high-grade squamous intraepithelial lesions (HSIL). We will use the Bethesda System (2014) terminology throughout this atlas.
The morphology of LSIL (including human papillomavirus (HPV)-associated changes) on the ThinPrep slide is essentially identical to LSIL on the conventional Pap. In part, this similarity is due to the ability of the mature squamous cell to maintain its integrity in spite of inadequate fixation or smear artifact inherent with the conventional smear. This integrity is a result of cell rigidity due to cytoplasmic keratinization.
Because of their morphology, cells derived from low-grade lesions are among the most easily located and recognized of intraepithelial abnormalities. Comparatively, LSIL nuclei are the largest and exhibit a lower N/C ratio than HSIL or carcinoma. These cells have greater nuclear atypia than ASCUS, exhibited as increased nuclear size, chromatin irregularity and irregularity of the nuclear envelope. Nuclei may occasionally not be as hyperchromatic as on conventional smears, but they are always hyperchromatic compared to the surrounding normal cells. The HPV-associated changes (e.g. cavitation of the cytoplasm) are more prominent due to the wet fixation as well as the transfer technique, which eliminates cell distortion caused by the conventional smearing method. The ThinPrep method better preserves these cell changes allowing for easier differentiation between true HPV-induced cytoplasmic cavitations and benign/degenerative vacuoles and/or glycogenated squamous cells.
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LSIL
LSIL
CIN1
Same Patient, Split Sample
Cells have distinct cytoplasmic borders indicating mature squamous and metaplastic cells. 60X
Cells appear predominantly single, in flat sheets or cobblestone arrangements. 60X
Nuclei are enlarged 3-4 times the size of a normal intermediate cell nucleus. 60X
Nuclei will vary slightly in size and shape. 60X
Binucleation or multinucleation may be evident in the presence of HPV. 60X
Nuclei exhibit smooth to slightly irregular nuclear membranes. 60X
Chromatin is slightly more coarse, but evenly distributed — it may appear degenerated or “smudged” if HPV
cytopathic effects are evident. 60X
Slight hyperchromasia is exhibited. 60X
Squamous cells must present with clear, well-defined cytoplasmic cavitations with a dense peripheral rim of
cytoplasm along with the above criteria to be diagnostic for LSIL with HPV cytopathic changes. 60X
Large perinuclear halos or vacuoles without the above criteria do not fall into this category. 40X
Because the cells are mature squamous cells, they retain their polygonal shape and for the most part retain their normal size. The nuclei are enlarged at least 3-4 times that of the normal intermediate cell nucleus, however, when HPV changes are evident, the cells may be smaller (almost parakeratotic) and the nuclei may also be smaller and somewhat pyknotic appearing with binucleation and/or multinucleation present. These pyknotic nuclei will also exhibit abnormal features such as hyperchromasia, increased size from that of the normal superficial squamous cell and a slight variation in shape and size. It is important to stress that an interpretation of LSIL/HPV requires both clear-cut cytoplasmic cavitations accompanied by the abnormal nuclear morphology described above.
Some SIL cases exhibit a mixture of LSIL and HSIL cells, and the most severe abnormality should take precedence when interpreting the ThinPrep. Occasionally it is difficult to distinguish LSIL from HSIL. Features favoring HSIL include a high N/C ratio, immature cytoplasm, and greater nuclear abnormalities. Rare SIL cases cannot be categorized either due to paucity of abnormal cells or truly intermediate criteria. Such cases may be more likely to progress, and an interpretation of “SIL, grade cannot be determined” or similar terminology is most prudent. While biopsy follow-up studies of LSIL will most frequently show low grade biopsy changes, about 15-20% of LSIL cases are followed by high grade biopsies.
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LSIL in accompaniment of an organism (Candida in this case) is still readily identifiable on the ThinPrep Pap Test. 60X
LOOK-ALIKE ENTITES (Differential Diagnoses):
True to form, LSIL has a few key look-alike entities, although they are somewhat easier to differentiate because of the immediate fixation with the ThinPrep® Pap Test resulting in better visualization of the cells and their features. For the differential criteria and images of LSIL to ASCUS, refer to the ASCUS chapter.
| REACTIVE (organism or inflammation) |
Repair (typical) |
LSIL (HPV) |
|
| Cellular Presentation | Single or in sheets | Flat sheets and groups | Single or in sheets |
| Cell Type | All cell types affected | Endocervical/ metaplastic cells | Mature squamous cells |
| Nuclei |
Enlarged up to 1.5 times Binucleation/ multinucleation may be present Nuclear membranes smooth |
Variable enlargement -slight to marked Binucleation/ multinucleation may be present Nuclear membranes smooth |
Enlarged 3-4 times Binucleation/ multinucleation may be present with HPV Nuclear membranes smooth to slightly irregular |
| Chromatin |
Finely granular, evenly distributed Hyperchromasia not evident |
Finely granular, evenly distributed Hyperchromasia not evident |
Finely to coarsely granular, evenly distributed Slightly hyperchromatic |
| Nucleoli | Small and often multiple, uniform | Small to conspicuous and often multiple | Inconspicuous or absent |
| Cytoplasmic Presentation | Peri-nuclear halos often present, small, multiple vacuoles may be evident due to degeneration | Vacuolated cytoplasm with loose tissue culture presentation | Dense, polygonal shape with or without clear, well defined HPV cavitation and a peripheral dense rim of cytoplasm |
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Reactive 60X
Repair 60x
LSIL/HPV 60X
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