Dermatofibroma (Benign Fibrous Histiocytoma)



Dermatofibroma (Benign Fibrous Histiocytoma)


David S. Cassarino, MD, PhD









Classic dermatofibroma shows a dermal-based proliferation of bland spindled to histiocytic-appearing cells, associated with a Grenz zone and overlying epidermal hyperplasia and basilar pigmentation.






Higher power examination of a classic dermatofibroma shows a proliferation of bland spindled to histiocytoid cells entrapping numerous hyalinized balls of collagen image.


TERMINOLOGY


Abbreviations



  • Dermatofibroma (DF)


  • Fibrous histiocytoma (FH)


Synonyms



  • Cutaneous fibrous histiocytoma


  • Sclerosing hemangioma


  • Histiocytoma


  • Epithelioid cell histiocytoma


Definitions



  • Common, benign, limited proliferation of mesenchymal cells in dermis


  • Lineage not well defined, although commonly referred to as “fibrohistiocytic”


ETIOLOGY/PATHOGENESIS


Unknown



  • Evidence supports both reactive and neoplastic pathogenesis



    • Histiocytic population may be clonal; fibroblast/myofibroblastic population may be polyclonal (reactive)


  • Tumor may be preceded by local trauma, including insect bite in some cases



    • However, often no inciting event identified


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Common tumors in most populations


  • Age



    • All ages, but most common in 4th and 5th decades


  • Gender



    • Affects males and females equally


Site



  • Typically occur on distal extremities but may present at any cutaneous site


Presentation



  • Firm, isolated, flesh-colored subcutaneous papule or nodule



    • New DFs are typically pink (vascular); older DFs are brown (overlying melanocyte hyperplasia)


  • Multiple DFs occur in immunosuppressed populations


  • “Dimpling” sign when in vivo DF is pinched by fingers


Treatment



  • Excision usually curative


Prognosis



  • Excellent in vast majority of cases



    • Local recurrence potential significant (up to 30%) with cellular variant


    • Metastasis and death from some cellular and atypical tumors reported



      • Usually large and deep lesions


MACROSCOPIC FEATURES


General Features



  • Firm, circumscribed but nonencapsulated, dermalbased tumor


  • White to yellow cut surface


  • Can have cystic changes and hemorrhage


MICROSCOPIC PATHOLOGY


Histologic Features



  • Dermal-based proliferation of typically bland spindled to histiocytic-appearing cells



    • Either spindled (fibroblastic) or histiocytoid cells may predominate



    • Early lesions typically show more histiocytes and lymphocytes


    • Established lesions show greater cellularity and spindled cells


    • Older lesions show more fibrosis


    • Spindled cells show elongated eosinophilic cytoplasmic processes


    • “Histiocytic” type cells are larger, epithelioid-shaped, and have abundant pale vacuolated cytoplasm


    • Cytologic atypia and pleomorphism are usually minimal


  • Tumors are grossly circumscribed but microscopically have irregular, often jagged borders


  • Collagen trapping at periphery



    • Spheres of intensely eosinophilic collagen (socalled “collagen balls”) separated by bands of pale fibrohistiocytic cells


  • Grenz zone



    • Tumor often spares band of superficial dermis


  • Folliculosebaceous induction and basilar epidermal hyperplasia overlying DF



    • Can mimic basal cell carcinoma if basilar induction is marked


  • Adjacent adnexal hyperplasia


  • Overlying melanocyte hyperplasia occasionally seen



    • So-called “dirty sock” sign


Predominant Pattern/Injury Type



  • Ill-defined borders


  • Nodular proliferation


  • Fibrous


  • Histiocytic


Predominant Cell/Compartment Type



  • “Fibrohistiocytic”


Histologic Subtypes

Jul 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Dermatofibroma (Benign Fibrous Histiocytoma)
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