Atypical Squamous Cells

Atypical Squamous Cells

• Originated from the Papanicolaou Class system as Class II.
• Descriptive criteria of atypia were provided by Patten in the 1970s.
• ASC-Us and ASC-H were created by Bethesda 2001.
• Squamous atypia includes intermediate or superficial cells with minimally abnormal nuclei, and atypical metaplastic atypia.

Atypical Squamous Cells of Undetermined Significance

• Papanicolaou mentioned "Atypical" in his 1943 Atlas.
• The Papanicolaou classification in the 1950s included a category (Class II) for atypical cells.
• In 1988, the Bethesda system defined "atypical cells of undetermined significance (ASCUS) as squamous abnormalities that are more marked than reactive changes, but fell short of being diagnostic of an SIL.
• In the 2001 Bethesda system, ASCUS became ASC-US, and ASC-H was added as another category.
• Squamous Atypia involves intermediate or superficial cells with a “sick” nucleus.
• Nuclear abnormalities are less marked than in mild or low grade dysplasia.
• Nuclei are enlarged about 2-3 times the area of an intermediate nucleus, i.e. 75 - 120um2.
• The average nuclease size in Dysplasia = 165um2.
• Nuclear membranes are generally smooth or only slightly irregular.
• Chromatin is fine, slightly hyperchromatic, but not course.
• Chromocenter formation is normally absent in both squamous atypia and mild dysplasia.
• The cytoplasm is thin, delicate and transparent like the cytoplasm of a mature intermediate or superficial cell.
• Cytoplasm can stain blue, pink or even orange.
• Dysplastic cytoplasm is usually slightly thick and dense like a slightly immature cell.
• Differential diagnosis includes: Marked reactive changes and Mild dysplasia.

Atypical Squamous Metaplasia

• Atypical squamous metaplasia is characterized by nuclear abnormalities less marked than in dysplasia in metaplastic cells.
• Nuclei are 1.5 - 2 times the size of a normal metaplastic nucleus or 2-3 times the size of an intermediate nucleus.
• Nuclei are comparable to squamous atypia with smooth to slightly irregular membranes and potential chromocentres or nucleoli.
• Cytoplasm is diminished and dense with sharply defined borders; high N/C ratios are like normal metaplastics.
• It is extremely difficult to diagnose cytologically.
• Differential Diagnosis includes: Benign metaplasia, Metaplastic dysplasia, ASC-H

ASC - Cannot Exclude High Grade Squamous Intraepithelial Lesion ASC-H

• ASC-H includes true HSIL and its mimics because of interpretive difficulty.
• Cells resemble immature parabasal or basal squamous cells.
• Nuclei are slightly enlarged, usually hyperchromatic, and have irregular outlines.
• Differential diagnosis includes Benign metaplasia, reactive metaplasia, H-SIL, atypical repair, atypical parakeratosis, and atypia of atrophy.
• HCG's can be placed in ASC-H category when cytological findings are suspicious but not definitive.

Included in ASC

• Cells that suggest a squamous intraepithelial lesion but are too scarce or degenerated for definitive SIL interpretation can be placed in the ASC category.
• Atypical parakeratosis, atypical repair, squamous atypia, inconclusive koilocytes, and hyperchromatic crowded groups can be included in the ASC category.
• It is often referred to as the wastebasket category.
• Reactive cellular change, reactive atypia, and inflammatory atypia, benign atypia, hyperkeratosis, parakeratosis, inflammatory changes, trich halos, glycogenated cells, benign metaplasia, and atrophy are NOT included.