Dermatofibroma (fibrous histiocytoma)

Editor: unassigned

Clinical Features:

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.

Histologic Features:

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.
Variants:
- 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