Lower anogenital squamous terminology

Introduction

This page describes the evolution of terminology used to describe the condition previously known as vulval intraepithelial neoplasia (VIN). In 2015, the International Society for the Study of Vulvovaginal Disease (ISSVD) adopted the term vulvar (vulval) squamous intraepithelial lesion (SIL). If you don't find what you are looking for in this list, try our general glossary, Topics A–Z index or the DermNet search box.

Vulval intraepithelial neoplasia

Traditionally, pathologists classified VIN into 3 grades: VIN 1, 2 or 3, in keeping with cervical intraepithelial neoplasia (CIN 1, 2, 3).

In 2004, the International Society for the Study of Vulvovaginal Diseases (ISSVD) reclassified VIN. They recommended that the term VIN 1, previously used to describe a mild change in the lower epithelial lining, should no longer be used, as these changes have been found to be due to irritation or non-precancerous viral wart infection and often clear up without treatment. The ISSVD recommended that the term VIN should be used for high-grade abnormal squamous lesions (these were previously known as VIN 2 and VIN 3).

VIN (usual-type or undifferentiated type) can be described by the pathologist as warty, basaloid or mixed VIN. These types of VIN are due to infection with cancer-forming (oncogenic) types of human papillomavirus (HPV) and are more likely to occur in women who smoke. It can be solitary or multicentric.

A less common ‘differentiated’ type of VIN is not caused by human papillomavirus and is associated with rapidly growing squamous cell carcinoma. It arises in about 5% of women with lichen sclerosus or erosive lichen planus. It is usually solitary.

VIN, unclassified type, is rare and is of unknown origin.

SIL

In 2012, a consensus committee of the College of American Pathologists and the American Society for Colposcopy (the LAST Committee) preferred the term squamous intraepithelial lesion (SIL) to vulval intraepithelial neoplasia (VIN). This classification was accepted by World Health Organisation (WHO) in 2014.

The LAST Committee recognised two grades.

• High-grade SIL (HSIL)
• Low-grade SIL (LSIL)

High-grade SIL has potential to progress to invasive SCC, whereas low-grade lesions are low risk.

2015 ISSVD Terminology of Vulvar Squamous Intraepithelial Lesions

The terminology adopted by the ISSVD in 2015 has 3 parts.

HSIL is associated with human papillomavirus infection. The differentiated type of VIN is associated with inflammatory skin diseases lichen sclerosus and lichen planus.