- Most common in young to middle-aged adults
- Small nodule or papule
- The overlying skin may erythematous or hyperpigmented and often shows the "dimple sign": central dimpling when the lateral borders of the lesion are compressed.
- Benign; rarely recurs, with the exception of the cellular and aneurysmal variants
- The aneurysmal variants may attain a large size, raising concern clinically for a malignant neoplasm.
- A heterogeneous tumor, with a number of variants (described below)
- All variants show a fairly well-circumscribed dermal proliferation of spindled "fibrohistiocytic "in tight fascicles, with a storiform pattern
- Cytologically, the cells have vesicular nuclei with scant to fairly abundant amphophilic cytoplasm.
- The cells characteristically wrap themselves around dermal collagen bundles, which may be hyalinized.
- Admixed lymphocytes, histiocytes, xanthoma cells and/or Touton-type giant cells may be present.
- The overlying epidermis is usually acanthotic and often hyperpigmented, but may instead sometimes show thinning.
- Occasionally, extension into the superficial subcutaneous fat may be present.
- Sclerosing hemangioma: a highly vascular dermatofibroma
- Hemosiderotic histiocytoma: a dermatofibroma with extensive hemosiderin deposition
- Aneurysmal benign histiocytoma: highly cellular variant with multiple pseudovascular spaces (devoid of an endothelial lining)
- Dermatofibroma with monster cells (atypical benign fibrous histiocytoma): an otherwise typical dermatofibroma with scattered bizarre giant cells
- Epithelioid benign fibrous histiocytoma: comprised of polygonal or rounded cells with abundant eosinophilic cytoplasm, frequently showing binucleation. Often exophytic with a collarette.
- Cellular variant: highly cellular often mimicking DFSP or leiomyosarcoma. Often shows focal necrosis and extension into the subcutaneous fat.
- Palisading variant: focal prominent nuclear palisading
- Clear cell dermatofibroma: composed predominantly of clear cells