Verruca vulgaris

What is verruca vulgaris?

Verruca vulgaris is a non-cancerous growth caused by infection with human papillomavirus (HPV). The growth is made up of abnormal squamous cells and it is typically found on the skin although it can also be found on the lips or inside the mouth. People who are immune-suppressed are at increased risk for developing verruca vulgaris. Another name for verruca vulgaris is the common viral wart.

Squamous cells

Squamous cells are specialized cells that are normally found on the surface of the skin and lips and on the inside of the mouth, esophagus, large airways, cervix, and anal canal. Squamous cells are strong cells that can withstand injury better than other types of cells. When examined under the microscope, squamous cells are large pink cells that connect together to form a barrier called the epithelium. This barrier on the surface of the skin is given the special name epidermis.

What causes verruca vulgaris?

Verruca vulgaris is caused by squamous cells becoming infected with HPV. There are many different types or strains of HPV and most cases are caused by low-risk types such as type 1, 2, 4, and 11. These types are called low-risk because unlike high-risk types of HPV (such as 16 and 18) they rarely cause the cells to become cancerous. Once the squamous cells become infected with HPV, they start to divide faster than the normal, uninfected cells. This leads to an increased number of cells and over time a noticeable growth. Pathologists use the words hyperplasia or hyperplastic to describe an increased number of non-cancerous cells.

How do pathologists make this diagnosis?

The diagnosis of verruca vulgaris can be made after a small piece of the growth is removed in a procedure called a biopsy or after the entire growth is removed in a procedure called an excision. The tissue is then sent to a pathologist who examines it under the microscope.

verruca vulgaris skin

When examined under the microscope, verruca vulgaris is made up of the same specialized squamous cells that are normally found on the surface of the skin and on the inner surface of the mouth. The squamous cells connect together to form long finger-like projections of tissue that stick out from the surface of the tissue. Pathologists describe these finger-like projections as papillary and the pattern of growth as exophytic which means growing outward. The surface is often covered by a thick layer of keratin. Abnormal-looking squamous cells with dark, irregular-shaped nuclei are often seen near the surface of the tissue. Pathologists call these cells koilocytes and they are a specific feature of HPV infection.

Your pathologist may not be able to see all of these microscopic features when only a small tissue sample is available for microscopic examination. In that case, your pathology report may describe the features as verrucous hyperplasia. This term is used to describe a group of abnormal growths that show features that overlap with verruca vulgaris.

by Jason Wasserman MD PhD FRCPC (updated August 27, 2021)
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