Cervical squamous intraepithelial lesions (LSIL, HSIL)
- Lesion
Cervical precancer is graded by how far up the epithelium the immature, abnormal cells reach. Low-grade lesions mostly go away; high-grade ones are treated.
What it is
Squamous intraepithelial lesions are the HPV-driven precursors of cervical squamous carcinoma. They are graded in two tiers: low-grade (LSIL, formerly CIN 1), which mostly reflects a productive HPV infection, and high-grade (HSIL, CIN 2 and CIN 3), in which immature atypical cells occupy at least the middle third of the epithelium. LSIL usually regresses, while HSIL persists or progresses more often and is treated by excision or ablation.
Structure
- Colposcopy: acetic acid turns abnormal epithelium white; high-grade lesions show sharp borders, mosaic and punctation of vessels.
- LSIL: preserved maturation with koilocytes (large, irregular, dark nuclei with a clear perinuclear halo) and binucleated cells in the superficial layers.
- HSIL: crowded immature basal-type cells with dark irregular nuclei extending upward; little cytoplasmic maturation; mitoses at all levels.
- The lesion may extend into endocervical glands (gland involvement), which is not invasion.
Step by step
- High-risk HPV infects the transformation zone and starts a productive infection (LSIL).
- Most infections are controlled by the immune system and the lesion disappears.
- When the infection persists and transforms the cells, immature atypical cells expand upward (HSIL).
- Without treatment, a fraction of HSIL acquires further changes and invades the stroma over several years.
Grading cervical squamous precursors
| Term | Old CIN term | How high the atypical immature cells reach | Usual handling |
|---|---|---|---|
| LSIL | CIN 1 | Lower third; koilocytes above | Follow-up; most regress |
| HSIL | CIN 2 | Into the middle third | Treatment, or close follow-up in young patients |
| HSIL | CIN 3 (carcinoma in situ) | Almost the full thickness | Excision (LEEP or cone) |
Markers
- p16 (diffuse in HSIL)
- Ki-67 (proliferation reaching the upper layers)
Clinical notes
- SIL causes no symptoms; it is found through cytology, HPV testing and colposcopy.
- Excision by loop electrosurgery or cone removes the lesion and gives tissue to check the margins and exclude invasion.
- After treatment, patients stay under surveillance because new or residual lesions can appear.
Test yourself
Think of the answer, then tap the question to see it.
What separates HSIL from LSIL under the microscope?
In HSIL, atypical immature cells extend at least into the middle third of the epithelium with loss of maturation and mitoses above the basal layer; in LSIL they stay in the lower third.
What is a koilocyte?
A squamous cell infected by HPV, with an enlarged, wrinkled, dark nucleus and a clear halo around it.
Does gland involvement by HSIL mean invasion?
No; the lesion is still intraepithelial, lying within glands lined by the same epithelium, although excision must remove it.
Elsewhere in DurgiPedia
Connections
Microorganisms1
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Cervical Cancer (StatPearls (NCBI Bookshelf), 2026); Cervical Cancer Screening (PDQ®)–Health Professional Version (National Cancer Institute, 2026).
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Representative model, for educational purposes only.