ANEURYSMAL DERMATOFIBROMA (BENIGN FIBROUS HISTIOCYTOMA);
FOLLICULAR INDUCTION (PSEUDOCARCINOMA) ALSO PRESENT
This is an uncommon variant of dermatofibroma (benign fibrous histiocytoma). A focus of prominent blood filled spaces, some of which are cavernous, within the background of a dermatofibroma (benign fibrous histiocytoma of skin) is characteristic. In this particular example, there is a focus of follicular induction having hair bulb features that could be mistaken for a basal cell carcinoma.

From an adult:
Direct scan of slide. The large blue area is the tumor.
Ordinary scan power view.
Low power view of area in yellow rectangle. There is specialized connective tissue of hair papilla type (HP) beneath a focus of follicular induction.
Medium power view of area in blue rectangle. Multinucleated histiocytes that contain hemosiderin are associated with small blood vessels and numerous fibrohistiocytic cells. This is ordinary dermatofibroma.
Medium power view of the junction of the vascular area and the tumor. Cavernous and capillary vascular spaces are present.
Medium power view of the junction of the tumor and the reticular dermis. This pattern of infiltration of native reticular dermis collagen bundles is characteristic of a dermatofibroma.

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