A high-grade squamous intraepithelial lesion (HSIL) is a term describing significant cellular changes found on the cervix, usually during a routine Pap test screening. This finding represents a severe, pre-cancerous abnormality in the surface cells of the cervix. Although an HSIL diagnosis is not cancer, it has a high potential to progress to invasive cervical cancer if left untreated. This result signals an immediate need for further diagnostic steps and medical management.
Defining the Condition
The terminology of high-grade squamous intraepithelial lesion describes the precise nature and severity of the cellular changes. “Squamous” refers to the flat cells that form the surface layer, or epithelium, of the cervix. “Intraepithelial” means the abnormal cells are strictly confined to this surface layer and have not yet invaded deeper tissues. This confinement differentiates HSIL from invasive cancer.
The designation “high-grade” indicates that the cells show significant disorganization and severe abnormalities under a microscope. These changes are classified as moderate to severe dysplasia, historically known as Cervical Intraepithelial Neoplasia (CIN) grades 2 and 3. Unlike Low-Grade SIL (LSIL), which often resolves spontaneously, HSIL rarely regresses. HSIL carries a substantially higher risk of progression to cancer, requiring timely treatment.
How HSIL Develops
The development of HSIL is almost exclusively linked to a persistent infection with high-risk types of the Human Papillomavirus (HPV). HPV is a very common virus, but types 16 and 18 are responsible for the majority of HSIL cases and subsequent cervical cancers. Most HPV infections are transient, meaning the body’s immune system clears the virus naturally within a year or two.
In a smaller subset of individuals, the high-risk HPV infection persists over an extended period. This persistent infection allows viral oncogenes, specifically E6 and E7, to interfere with the normal cell cycle regulation of the host cells. This sustained disruption leads to genetic damage and uncontrolled growth, resulting in the severe cellular abnormalities categorized as HSIL.
Confirming the Diagnosis
Following an abnormal Pap test suggesting HSIL, the next required step is a diagnostic colposcopy. A colposcopy uses a specialized microscope to provide a magnified view of the cervix. During the examination, a dilute acetic acid solution is applied, which temporarily turns abnormal cell growth white, allowing the clinician to precisely locate the lesion.
The most crucial element of the colposcopy is the directed biopsy, where small tissue samples are taken from the most abnormal areas. This tissue is sent to a pathologist for a definitive histological examination. The examination confirms the exact grade of the lesion and rules out any underlying invasive cancer. The final pathology report provides the definitive diagnosis, which guides the subsequent treatment plan.
Treatment and Follow-Up Care
The standard of care for HSIL focuses on excisional procedures designed to completely remove the abnormal tissue. The goal is to remove the entire transformation zone, the area of the cervix where abnormal cell changes typically begin. The most common procedure is the Loop Electrosurgical Excision Procedure (LEEP). LEEP uses a thin wire loop heated by an electrical current to precisely cut away a cone-shaped piece of tissue.
LEEP is often preferred because it can be performed in an outpatient setting using local anesthesia, resulting in a quick recovery time. Another effective method is the Cold Knife Cone Biopsy (CKC), which uses a surgical scalpel. CKC is more invasive, usually requiring general anesthesia, but it provides a clean specimen advantageous for a pathologist’s evaluation.
Both LEEP and CKC offer a high cure rate by removing the pre-cancerous tissue. Following the procedure, long-term surveillance is necessary to monitor for recurrence. Follow-up involves regular co-testing, including both a Pap test and an HPV test, typically performed every one to two years. This monitoring is essential because the underlying HPV infection may persist, keeping the risk of developing new lesions elevated.