This pathology video examines the microscopic features of dermatofibroma (DF), focusing specifically on the Lipidized or Ankle-Type variant. Low-power examination reveals classic features such as epidermal hyperplasia (flattened tabling) and peripheral collagen entrapment, which are crucial for diagnosis, especially since the cellular infiltrate at high power may display concerning features like atypia, pleomorphism, and scattered mitotic figures. The lipidized subtype is definitively characterized by a dense background of hyalinized pink collagen forming rings and arcs, interspersed with spindle cells exhibiting abundant pale, foamy (xanthomatous) cytoplasm. The video emphasizes the importance of these architectural clues and the presence of the dense collagen to distinguish this benign DF variant from a true xanthoma, noting that ankle-type DFs are not associated with serum lipid abnormalities.
0:03 Low-Power Architectural Features: The lesion shows beautiful epidermal hyperplasia with characteristic flattened tabling along the base of the rete ridges, and a cellular spindle cell proliferation in the dermis.
0:27 Peripheral Growth Pattern: The tumor margins are infiltrative, showing the characteristic DF feature of "trickling" between collagen bundles.
0:33 Adnexal Induction: The lesion demonstrates induction, including small basal islands, hair follicle roots, and sebaceous glands, often seen overlying or adjacent to DFs.
0:59 Entrapped Collagen: A classic pattern of DF is shown where individual collagen bundles at the periphery are wrapped and "trapped" by the tumor cells.
1:31 Key Diagnostic Principle: It is crucial to examine the low-power view and the periphery of the lesion first, as the center can look aggressive or confusingly cellular.
1:50 Acceptable Atypia: At high power, the cells may appear atypical, plump, pleomorphic, and possess large nuclei with nucleoli. The presenter stresses that this high-power cellular atypia is acceptable within the context of an otherwise typical dermatofibroma.
2:23 Mitotic Activity: Scattered mitotic figures are a common and benign finding, particularly in larger or highly cellular DFs.
3:03 Introducing the Variant: This specific subtype is the Lipidized or Ankle-Type dermatofibroma, characterized by dense, pink, hyalinized collagen bundles forming rings and arcs, along with cells that have abundant, pale, foamy cytoplasm (lipidization).
3:41 Location Correlation: This variant frequently occurs on the ankle or lower leg.
4:03 Distinguishing from Xanthoma: While the foamy cells resemble those of a xanthoma, the presence of the dense, sclerotic pink collagen is the essential clue distinguishing the lipidized DF from a true xanthoma.
6:50 Clinical Takeaway: Lipidized DFs are totally benign and, unlike some xanthomas, are generally not associated with systemic lipid abnormalities.