Low-grade squamous intraepithelial lesion (LSIL) is a non-cancerous disease that develops in the skin on the surface of the vulva. Although LSIL is considered a non-cancerous disease, there is a very small risk that it will turn into cancer over time. However, for most patients with LSIL, the immune system will remove the abnormal cells and the vulva will return to normal. LSIL of the vulva was previously called vulvar intraepithelial neoplasia (VIN1) and some reports may still use this terminology. A similar condition with the same name (LSIL) can develop in the cervix or vagina.
The vulva is the external part of the female genital tract. It forms the opening of the vagina and includes the mons pubis, labia majora, labia minora, and clitoris. The vulva is composed of skin. The surface of the skin is called the epidermis and is made up of squamous cells. The tissue beneath the epidermis is called the dermis, it contains blood vessels and connective tissue.
Low-grade squamous intraepithelial lesion in the vulva is caused by a virus called human papillomavirus (HPV). The virus infects the squamous cells in the epidermis. Once inside the cell, the virus changes the cell and prevents it from developing normally. Pathologists call this change dysplasia. There are many types of HPV and LSIL can be caused by both the low-risk (HPV 6 and 11) and high-risk (HPV 16 and 18) types.
The diagnosis of LSIL is usually made after a small sample of tissue is removed in a procedure called a biopsy. The affected areas are usually treated with topical or laser therapy. A larger biopsy or excision may be performed to look for features of related, but more serious conditions called high-grade intraepithelial lesion (HSIL) and squamous cell carcinoma. When examined under the microscope, squamous cells infected with HPV are much larger than normal squamous cells and are called koilocytes.