Low-grade squamous intraepithelial lesion (LSIL) is a non-cancerous disease that develops on the inside surface of the vagina. 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 infected cells and the vagina will return to normal. LSIL was previously called vaginal intraepithelial neoplasia (VAIN1) and some reports may still use this terminology. A similar condition with the same name (LSIL) can develop in the cervix or vulva.
The vagina is part of the female genital tract. It forms a canal that starts at the cervix and ends at the vulva on the outside of the body. The inside of the vagina is lined by specialized cells called squamous cells that created a barrier called the epithelium. The tissue beneath the epithelium is called the lamina propria and contains blood vessels and connective tissue. Together, the epithelium and lamina propria are called the mucosa.
Low-grade squamous intraepithelial lesion in the vagina is caused by a virus called human papillomavirus (HPV). The virus infects the squamous cells in the epithelium. 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. When examined under the microscope, squamous cells infected with HPV are much larger than normal squamous cells and are called koilocytes. Biopsies from the vulva and cervix may also be taken to look for a similar condition in those areas. Additional treatment is not always required.