DERMATOFIBROMA ASSOCIATED WITH FOLLICULAR INDUCTION (PSEUDOCARCINOMA)
Hyperplasia of basaloid cells over a dermatofibroma can be misinterpreted as basal cell carcinoma. The number of foci of proliferation per linear horizontal unit exceeds the number of follicles expected for the same measurement, so this does not logically represent normal follicles that are impeded in their growth by the underlying dermatofibroma. These foci are often associated with stroma that is abnormal for the papillary or reticular dermis, and, on occasion, this stroma is of the type found in a hair bulb papilla. It is interesting that foci having these features are sometimes found in the background of a nevus sebaceus of Jadassohn and also misinterpreted as basal cell carcinoma. On occasion, multiple subunits of the pilosebaceous unit may be present. True basal cell carcinomas are rarely found in this background, and some of these have tumor necrosis, small strand patterns of infiltration, or prominent retraction.
 
Scan power view. Numerous foci of proliferation of basaloid cells are connected to the epidermis, and two foci appear to be in the superficial dermis. The dermatofibroma occupies the entire reticular dermis as represented in this biopsy.
Low power view of the surface.
High power view of the upper right part of the picture above. There is condensation of the epithelial cells of the type found in hair bulbs in the left side of this focus of proliferation. The stroma is not of classical hair bulb papilla type, but is abnormal for the papillary dermis.
Medium power view of the two clusters of cells in the dermis of the low power view. The one on the right is associated with specialized stroma of the type that can be seen in trichoepitheliomas. These structures, as seen in this field, could still be misinterpreted as basal cell carcinoma.
Medium power view of the same two structures as seen in deeper sections. The follicular nature of these is apparent in this field.
Medium power view of the middle of the dermis. Spindle cells having the features of fibroblasts are intermingled with collagen bundles of the type characteristic of the reticular dermis. Vascularity is slightly increased. This is one of several patterns that is diagnostic for a dermatofibroma.

Click on your browser's 'Back' button to return to the previous page.