[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Female genital tract](https://durgical.com/en/general-pathology/areas/female-genital/) › Cervical squamous intraepithelial lesions (LSIL, HSIL)

# 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.

Updated Nov 12, 2026

## Key points

- LSIL (CIN 1): atypia and mitoses in the lower third; koilocytes in the upper layers; mostly regresses and is usually observed.
- HSIL (CIN 2): atypical immature cells reach the middle third; HSIL (CIN 3): nearly full thickness, carcinoma in situ.
- HSIL features: high nuclear-to-cytoplasmic ratio, loss of maturation, mitoses above the basal layer (some abnormal), diffuse p16.
- Natural history: most LSIL regress, a minority persist and only a few progress; HSIL regresses less and carries a real risk of invasion if left untreated.
- Peak age of SIL is younger than the peak age of invasive carcinoma, a gap of years that screening uses.

On this page

- The basics Key points
- What it is
- Structure
- Step by step
- Grading cervical squamous precursors
- Markers
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Clinical notes

- Study Test yourself

- Connections Connections

## 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](https://durgical.com/en/conditions/cervical-intraepithelial-neoplasia/) | CIN 1 | Lower third; koilocytes above | Follow-up; most regress |
| [HSIL](https://durgical.com/en/conditions/cervical-intraepithelial-neoplasia/) | CIN 2 | Into the middle third | Treatment, or close follow-up in young patients |
| [HSIL](https://durgical.com/en/conditions/cervical-intraepithelial-neoplasia/) | 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.

## Memory aid

Count the floors the abnormal cells have climbed: one floor is low grade, two floors or the whole building is high grade.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/cervical-squamous-intraepithelial-lesions/)

[More Pathology questions →](https://durgical.com/en/practice/?f=pathology)

## Elsewhere in DurgiPedia

- [Cervix and vagina: the transformation zone](https://durgical.com/en/histology/cervix-and-vagina-the-transformation-zone/)

## Connections

## Related 6

- [HPV and cervical carcinogenesis](https://durgical.com/en/general-pathology/hpv-and-cervical-carcinogenesis/)
- [Invasive cervical carcinoma](https://durgical.com/en/general-pathology/invasive-cervical-carcinoma/)
- [Cervical cancer screening and prevention](https://durgical.com/en/general-pathology/cervical-cancer-screening-and-prevention/)
- [Dysplasia and carcinoma in situ](https://durgical.com/en/general-pathology/dysplasia-and-carcinoma-in-situ/)
- [Cytology: the Pap test, fine-needle aspiration and body fluids](https://durgical.com/en/general-pathology/cytology-the-pap-test-fine-needle-aspiration-and-body-fluids/)
- [Biopsy: excisional, incisional, core needle, punch and fine-needle aspiration](https://durgical.com/en/general-pathology/biopsy-excisional-incisional-core-needle-punch-and-fine-needle-aspiration/)

## Related conditions 4

- [Cervical intraepithelial neoplasia (cervical dysplasia)](https://durgical.com/en/conditions/cervical-intraepithelial-neoplasia/)
- [Human papillomavirus (HPV) infection](https://durgical.com/en/conditions/human-papillomavirus-infection/)
- [Cervical cancer](https://durgical.com/en/conditions/cervical-cancer/)
- [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/)

## Microorganisms 1

- [Human papillomavirus](https://durgical.com/en/microbiology/human-papillomavirus/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

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](https://www.ncbi.nlm.nih.gov/books/NBK431093/) (StatPearls (NCBI Bookshelf), 2026); [Cervical Cancer Screening (PDQ®)–Health Professional Version](https://www.cancer.gov/types/cervical/hp/cervical-screening-pdq) (National Cancer Institute, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/general-pathology/cervical-squamous-intraepithelial-lesions/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/cervical-squamous-intraepithelial-lesions/