Possible Contribution of Consistent Epidermal Attenuation to the Pearly Appearance of Facial Basal Cell Carcinoma

Basal cell carcinoma (BCC) and intradermal nevus (IN) can be difficult to distinguish clinically, even with dermoscopy, because IN may exhibit dermoscopic features similar to those of BCC. In contrast, the pearly appearance characteristic of BCC is usually absent in IN and may serve as an important diagnostic clue. We hypothesized that attenuation of the overlying epidermis might contribute to this appearance by enhancing surface reflection and increasing the visibility of underlying dermal components. We retrospectively evaluated 27 non-ulcerated facial BCCs (25 nodular and 2 morpheaform) and compared them with facial INs (n = 19), malignant melanomas (MM; n = 6), Merkel cell carcinomas (MCC; n = 3), and mixed tumors (MT; n = 4). Epidermal thickness and hair follicle density were quantitatively assessed in lesional and adjacent normal skin. Dermal mucin deposition and collagen staining intensity were also evaluated. The lesional epidermis was thinner than the adjacent normal epidermis in all 27 BCCs. The lesional-to-normal epidermal thickness ratio was significantly lower in BCC than in IN. The lesional-to-normal hair follicle density ratio was also significantly lower in BCC than in IN. Superficial dermal mucin deposition was observed in all BCCs but not in the other tumor types, whereas the lesional-to-normal collagen staining intensity ratio was comparable between BCC and IN. A pearly appearance was observed in all 25 nodular BCCs but not in the two morpheaform BCCs despite epidermal attenuation. None of the other tumor types exhibited a pearly appearance, including MM lesions with epidermal attenuation. These findings demonstrate that epidermal attenuation is a consistent histopathological feature of non-ulcerated nodular BCC and raise the possibility that it contributes to the characteristic pearly appearance of nodular BCC. However, because epidermal attenuation was also observed in lesions without a pearly appearance, its actual contribution remains uncertain and requires further investigation.