High-grade Squamous Intraepithelial Lesion of the Vulva with Obscuring Edema: A Potential Diagnostic Pitfall in Vulvar Biopsies

The authors describe the clinicopathologic features of high-grade squamous intraepithelial lesion (HSIL) of the vulva with associated epidermal edema that was significant enough, at least focally, to obscure their underlying features in biopsies. Eleven such cases (study group) were compared with a control group of 33 HSIL cases without obscuring edema regarding a variety of clinicopathologic features. In the study group cases, the changes were diffuse and involved most of the epidermis. The low power impression was generally of florid spongiosis (n=11) and/or surface degradation (n=3). A dense lichenoid infiltrate was concurrently present in 73% of cases. Classic HSIL areas were focally apparent either at the basal regions of the epidermis (n=2) or within the epidermis (n=4) in 6 cases. High-power inspection showed features of HSIL, including hyperchromasia and at least moderate pleomorphism in all cases, but large zones of apparently reduced atypia were often present in the edematous areas. Mitotic figures were clearly less conspicuous in the study group cases, especially in the edematous areas. Compared to controls, the study group cases showed a statistically significant lower mitotic index, a higher frequency of a dense lichenoid inflammation, and a lower frequency of overlying hyperkeratosis. These two groups showed no significant differences regarding a variety of other morphologic features. All cases in both groups were p16 block positive and showed a high proliferative index. The study and control groups showed no significant differences regarding patient age, duration of symptoms, frequency of use topical vulvovaginal treatments during the month before presentation, lesional focality, history of lichen sclerosus, or location of the lesion. In summary, florid edema may obscure the underlying features of HSIL in vulvar biopsies. Practitioners should be aware of this potential diagnostic pitfall.