A Low Grade Squamous Intraepithelial Lesion (LSIL), commonly abbreviated as LSIL, occurs when a routine cervical cancer screening, such as a Pap test, detects mildly abnormal cells on the surface of the cervix. This result indicates a change in the cells that is not cancer, but rather a sign of a superficial cellular disruption. The diagnosis can understandably cause concern, but it is a frequent finding. LSIL is considered the least serious category of abnormal cell growth in the Bethesda System used for classifying Pap test results. This low-risk condition rarely progresses to a more serious problem and frequently resolves on its own without requiring any invasive treatment.
Understanding the Cellular Changes
Understanding the full name of the condition helps clarify what is happening at the cellular level. The term “squamous” refers to the thin, flat cells that form the outer layer of the cervix. “Intraepithelial” means the abnormal cells are confined entirely to the surface layer of tissue, known as the epithelium, and have not invaded deeper tissues.
The phrase “low grade” describes the degree of abnormality seen when a pathologist examines the cells under a microscope. These cells show only mild dysplasia, meaning they look only slightly different from healthy cells. This minimal change is also referred to as Cervical Intraepithelial Neoplasia Grade 1 (CIN 1). In contrast, a High Grade Squamous Intraepithelial Lesion (HSIL) involves moderate to severe dysplasia, indicating a greater degree of cellular disorganization and a higher potential for progression. Because the changes are so mild, LSIL is often a temporary state that the body’s immune system can easily clear.
The Role of Human Papillomavirus
The cause behind nearly all cases of LSIL is an infection with the Human Papillomavirus, or HPV. HPV is an extremely common virus transmitted through intimate skin-to-skin contact, and most sexually active people will contract it at some point in their lives. The virus infects the squamous cells, causing them to grow and divide in a disorganized way, which is what pathologists observe as LSIL.
There are over 100 different types of HPV, which are categorized based on their association with cancer risk. LSIL is often linked to the high-risk types of HPV, such as types 16 and 18, which are responsible for the majority of cervical cancers. However, the presence of a high-risk type does not mean a person has cancer; it means the cellular change that has occurred has a greater potential risk if the infection becomes persistent.
The body’s immune system effectively clears most HPV infections within two years. The risk of the lesion progressing to a higher-grade abnormality is much greater when the high-risk HPV infection persists over a long period. Therefore, the management approach focuses on monitoring the immune system’s ability to clear the virus and the lesion.
Confirming the Diagnosis After Screening
A Pap test that returns an LSIL result is a screening tool, not a definitive diagnosis, and requires further evaluation. The next step is typically a procedure called a colposcopy, which allows for a much more detailed examination of the cervix. A colposcopy involves the use of a specialized low-powered microscope to magnify the surface of the cervix.
During the colposcopy, the physician applies a mild vinegar-like solution to the cervix, which temporarily turns any abnormal areas white, making them highly visible. If an abnormal area is seen, a small tissue sample, or biopsy, may be taken for a definitive diagnosis. The biopsy is crucial because it confirms the grade of the lesion and rules out any underlying high-grade disease that the Pap test may have missed.
This diagnostic confirmation is necessary because only a fraction of women with an LSIL Pap result will have a true precancerous condition. The colposcopy procedure itself is generally quick, lasting only about 10 to 15 minutes, and any mild discomfort from the biopsy is brief.
Standard Management and Outlook
The standard medical management for LSIL is active surveillance, often described as “watchful waiting,” rather than immediate treatment. Studies show that approximately two-thirds of LSIL cases resolve spontaneously within two years.
The risk of progression to a high-grade lesion or invasive cancer is low, estimated to be around 11% over several decades if the lesion remains untreated. Treatment is typically reserved for cases where the LSIL persists for an extended period, such as two years or longer, or progresses to a high-grade lesion.
Surveillance usually involves repeating the Pap test and often the HPV test at regular intervals, such as every 12 months. This schedule allows the medical team to monitor whether the abnormal cells are regressing or show any signs of progression. Patients who smoke or have a weakened immune system, such as those with HIV, may have a lower rate of spontaneous regression, making follow-up appointments especially important.