Premalignant / preinvasive lesions - cytology
SIL-general (cyto)

Topic Completed: 1 June 2011

Minor changes: 18 February 2021

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PubMed search: squamous intraepithelial lesions [title] (SIL) cervix

Marilin Rosa, M.D.
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Cite this page: Rosa M. SIL-general (cyto). PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cervixcytologysil.html. Accessed April 19th, 2021.
Definition / general
  • SIL cells are usually detected by cytologic examination (conventional Pap smear or liquid based cytology)
  • SIL morphologic abnormalities correlate with cytogenetics, ploidy, cell proliferation and molecular changes
  • Increased risk in SLE and HIV patients (Arthritis Rheum 2004;50:3619)
  • Keratinized cells are nonspecific, associated with benign cellular changes such as parakeratosis or hyperkeratosis, ASCUS, as well as LSIL, HSIL and invasive squamous carcinoma
  • HPV hybrid capture: testing for high risk HPV with the HCT II test is useful to detect HSIL in LSIL groups and to select ASCUS patients for colposcopy but not for cervical cancer screening tests (Arch Pathol Lab Med 2001;125:1453); HCT II is more sensitive than a repeat smear in detecting high grade lesions in women with low grade lesions (Acta Obstet Gynecol Scand 2005;84:996)
  • Can also detect HPV using indirect PCR on Pap smears (Arch Pathol Lab Med 2001;125:353)
  • Low grade SIL (LSIL): usually euploid or polypoid, 2/3 regress, 1/6 progress, 1/6 are unchanged
  • High grade SIL (HSIL): usually aneuploid, less regression; 1/3 become invasive at 9 years; associated with HPV types 16, 18, 31, 33; peaks during age 30 - 39 years; 0.2% develop invasive carcinoma even after treatment; distinction between high grade dysplasia / HSIL and carcinoma in situ is not reproducible between pathologists and is not usually made anymore
  • Classification systems:
    1. Mild, moderate or severe dysplasia or carcinoma in situ
    2. Cervical intraepithelial neoplasia (CIN) - CIN I, CIN II, CIN III
    3. Low grade SIL (LSIL) or high grade SIL (HSIL) - SIL terminology is currently recommended
  • LSIL: controversial since most lesions regress
  • HSIL: cone, LEEP, electrodiathermy, cryosurgery, laser; long term follow up is necessary
  • Note: treatment of HIV+ patients must be more aggressive (Eur J Obstet Gynecol Reprod Biol 2005;121:226)
Cytology description
  • Similar histology as invasive cells, including nuclear enlargement and hyperchromasia, alteration of maturation, increased mitotic activity; also reduction in cytoplasmic glycogen (less iodine staining with Lugol or Schiller’s iodine test); no tumor diathesis
  • Usually cell borders are NOT well defined (CIN like changes with well defined cell borders implies reactive changes), nuclei are crowded and irregular with smudgy or granular chromatin
  • Keratinizing or nonkeratinizing
  • Includes cells with HPV cytopathic effect
Positive stains
Differential diagnosis
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