AIN


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  • Histology

    • LSIL
      • same as CIN1
      • 1/3 thickness dysplasia
      • mild nuclear atypia (mild hyperchromasia, NC ratio < 1:3, even chromatin)
      • loss of picket fence architecture
    • HSIL
      • SIL2
        • 2/3 dysplasia
        • moderate nuclear atypia (moderate hyerchromasia, NC ratio < 1:2)
      • SIL3
        • full thickness dysplasia
        • severe nuclear atypia (marked hyperchromasia, NC ratio > 2:3, clumpy chromatin)

  • Ddx

    • morphologically all non-neoplastic ddx lacks overt pleomorphism
    • basal cell hyperplasia
    • transitional cell metaplasia
    • squamous metaplasia
    • atrophy (dark, but thin and no mitosis)
    • atrophy with partial maturation (hyperchromasia, mitosis)
    • pseudokoilocytosis
    • reactive
    • radiation atypia
    • SCC
      • has invasion

  • Stains

    • get p16 and Ki67
    • p16 strong and diffuse in HSIL
    • p16 strong but scattered in LSIL with high risk HPV
    • p16 may be negative in LSIL with low risk HPV
    • p16 weak/negative in metaplasias
    • Ki67 is used as tie breaker for ambiguous p16 results
    • Ki67 is positive in inflammatory cells

  • Signout

    • *** grade intraepithelial lesion (***SIL, ***IN***)
    • if uncertain SIL2 vs SIL3: High grade intraepithelial lesion (HSIL, ***INII-III)
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