A Comparative Clinicopathological Study of Inverted Follicular Keratosis and Well-Differentiated Squamous Cell Carcinoma / 대한피부과학회지

ABSTRACT

Background@#Inverted follicular keratosis (IFK) is a benign tumor that occurs mainly as a single lesion in the head and neck. Histologically, the tumor lobules show endophytic or exophytic growth and are characterized by squamous eddies. IFK should be differentiated from seborrheic keratosis, verruca vulgaris, and squamous cell carcinoma (SCC).In particular, differentiating from well-differentiated SCC can be difficult when downward growth is observed along with some mitotic figures and inflammatory cell infiltration. @*Objective@#To evaluate and compare the clinical and histopathological characteristics of IFK and well-differentiated SCC. @*Methods@#We retrospectively reviewed the clinicopathological records of 21 patients diagnosed with IFK and 21 randomly assigned patients diagnosed with well-differentiated SCC between 2000 and 2022 at the Dermatology Department of the Yeungnam University Medical Center. @*Results@#IFK occurs frequently on the head and neck of middle aged and older adults, and its average size is less than 1 cm. Acantholysis was observed in varying degrees in IFK; however, well-differentiated SCC was mostly absent (17 cases) or mild (three cases) showing a statistically significant difference. Squamous eddies were observed in 21 cases of IFK and eight of well-differentiated SCC. The average number of dyskeratotic cells and mitotic counts did not differ significantly between IFK and well-differentiated SCC. @*Conclusion@#We suggested some evidence for the irritant origin of IFK. We also compared the clinicohistological findings of IFK with those of well-differentiated SCC and concluded that excluding atypical cells, abnormal mitotic figures, and irregular invasive borders is important for differential diagnosis.