Histologic Findings
A dilated follicular infundibulum extends deep into the dermis and, at times, into the subcutaneous tissue. The cavity is lined by the epidermis, which is atrophic near the follicular ostium. The epidermis is hypertrophic and proliferative in the deeper portion of the invagination where the numerous rete ridges project into the surrounding stroma. The cavity is filled with laminated keratin. Vellus hair follicles and small sebaceous lobules may be attached to the lower portion of the infundibulum. [12] Gonzalez-Guerra et al reported in 2008 that cutaneous adnexal tumors of the hair follicle can be identified using immunohistochemistry studies for calretinin, with differentiation towards cells of the outer root sheath. [13]

-
Hematoxylin and eosin stain. Original magnification X40. Courtesy of Lawrence Machtinger, MD.
-
Image shows an epidermal lining that is atrophic near the ostium but progressively hypertrophic and proliferative, with numerous rete ridges, in the deeper part of the cavity (hematoxylin and eosin, original magnification X100).
-
The cavity is filled with laminated keratin (hematoxylin and eosin, original magnification X100).
-
Dilated pore of Winer on forehead.
-
Dilated pores of Winer on forehead and lateral upper labial region.
-
Dilated pore of Winer on lateral upper labial region.