Skin / Soft Tissue Tumors - Benign fibrous histiocytoma

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Skin / Soft Tissue Tumors

Fibrohistiocytic Tumors

Benign fibrous histiocytoma (superficial)

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 23 October 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

See also deep benign fibrous histiocytoma

General
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● Storiform pattern of bland spindle cells and foamy histiocytes centered in dermis with possible extension to subcutis
● Variable hemosiderin, multinucleated giant cells, chronic inflammatory cells and pseudoepitheliomatous hyperplasia

Terminology
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● Also called dermatofibroma (particularly if sclerotic and hypocellular), dermal fibrous histiocytoma, sclerosing hemangioma, histiocytoma cutis
● Part of WHO classification for skin tumors, not soft tissue tumors
● See also Bone, Eye-Conjunctiva, Eye-Orbit and Heart chapters
● See also variants described separately - aneurysmal, angiomatoid, atypical, cellular, epithelioid, juvenile xanthogranuloma
● Other variants: lipidized, osteoclastic, myxoid, palisading, monster cell

Epidemiology
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● Very common benign, indolent tumor of adults, common site is legs of women 20-50 years old
● Slight female predominance
● May be associated with trauma
● Line of differentiation is uncertain
● Multiple lesions may be associated with immunosuppression (Int J Dermatol 2008;47:723)

Pathophysiology
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● Fibroblasts cause strong expression of keratin 19 by keratinocytes and production of a galectin1 rich extracellular matrix, which may account for pseudoepitheliomatous hyperplasia (J Dermatol Sci 2009;55:18)

Treatment and prognosis
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● Excision; local recurrence is rare even with involved margins
● Rarely is locally aggressive or metastatic (more common for facial lesions, with extension into subcutis)

Clinical description
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● Tan-brown (also pink-red, flesh colored, rarely blue), firm, mobile, painless papule < 2 cm in dermis
● Size varies slightly with time; rarely > 5 cm and plaque-like (Australas J Dermatol 2008;49:106) or pedunculated (Case Rep Dermatol 2011;3:32)
● Polypoid, flat, dome shaped or depressed
● May dimple upon lateral compression; may have overlying scaling

Clinical images
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Inward dimpling due to tumor binding to subcutis (arrow); source: UAB

Dimpling when squeezed along its margins; source: UCSF

Polypoid nodule with slim pedicle

Dermoscopy description
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● Wide range of presentations (Arch Dermatol 2008;144:75)
● Pigment network (72%, 3% are atypical), white scar-like patch (57%), different vascular structures (50%), white network (18%)
● May resemble melanoma

Dermoscopy images
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Pseudonetwork present

Central white scar-like patch surrounded by a pigmented network and many brown globules

Different patterns

Various images

Gross images
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Various images

Micro description
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● Well defined but non-encapsulated
● Overlying epidermis shows pseudoepitheliomatous hyperplasia and hyperpigmentation of basal cell layer
● Grenz zone is usually present
● Storiform pattern of spindled and bland fibroblasts and histiocyte-like cells in mid-dermis and subcutaneous tissue with infiltrative margins but sparing epidermis
● Loose collagenous and rarely myxoid stroma
● Spindle cells have scant cytoplasm, thin elongated nuclei with pointed ends
● Nuclei almost touch each other, unlike smooth muscle lesions
● Also foamy histiocytes with variable hemosiderin (Case Rep Dermatol 2011;3:32), some multinucleated giant cells, branching vessels & chronic inflammatory cells; rarely is marked eosinophilic infiltrate (European Journal of Dermatology 2011;21:138)
● Often Touton giant cells (superficial and filled with hemosiderin), individual hyaline collagen bundles surrounded by tumor cells at periphery
● 2% have 4 or more mitotic figures/10 HPF, but still benign behavior (J Cutan Pathol 2008;35:839)
● See also variants described separately - aneurysmal, angiomatoid, atypical, cellular, epithelioid, juvenile xanthogranuloma
● Rare variants are balloon cell (Am J Dermatopathol 2007;29:197), clear cell, osteoclast like giant cells, signet ring (Am J Dermatopathol 2009;31:84)

Micro images
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Tumor is more basophilic than surrounding dermis

Basophilia is due to increased cellularity

Sharp border between tumor and subcutis

Tumor cells are composed of histiocyte-like cells and foam cells

Tumor cells are mostly fibrous in this focus

Fat may be entrapped at edge, but must differentiate from infiltration of DFSP

Randomly arranged foam cells, fibroblasts and histiocyte-like cells; foam cells are somewhat specific for this lesion

Foam cells vary from none (top), mixed (middle) to predominating (bottom)

Less common finding of predominately foam cells and cholesterol clefts

Epithelial hyperplasia-left side shows squamous / basaloid differentiation, right side shows follicular differentiation

Cellularity changes over time from subtle increase in fibroblasts (fig A) to cellular tumor (fig B/C) to sclerotic Lesion (fig D-right side)

Vulvar tumor has uniform spindle cells confined to dermis

Various images

H&E and D2-40

Other images: tumor with hyperplastic epithelium #1; #2; hyperplastic epidermis and sclerotic stroma #1; #2; #3; foam cells with vacuolated cytoplasm; fibroblastic cells with vacuolated cytoplasm in collagenous stroma; spindle cell nodule; paucicellular dermal tumor; spindle cells in dense collagenous stroma

Positive stains
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● Highly variable immunohistochemical profile
● Vimentin, Factor XIIIa, CD34 (only in cellular variant)
● Also tenascin at dermoepidermal junction (Hum Pathol 2001;32:50); variable calponin (65%), actin, desmin, myosin, D2-40 (Mod Pathol 2010;23:434)
● Early lesions are reactive for CD68 (Ann Dermatol 2010;22:333)

Negative stains
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● CD68, CD34, BCL2, desmin
● Ki-67 < 10% (Arch Pathol Lab Med 2006;130:831)

Molecular/cytogenetics description
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● Often clonal

Differential diagnosis
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● Atypical fibroxanthoma: characteristic gross appearance, storiform pattern not prominent, marked pleomorphism
● Dermatofibrosarcoma protuberans: “tight” storiform pattern, infiltrative, more cellular, no foam cells, CD34+
● Kaposi’s sarcoma: vascular tumor with red blood cell extravasation
● Leiomyoma or leiomyosarcoma: confusion based primarily on variable staining of benign fibrous histiocytoma for muscle markers
● Low grade myofibroblastic sarcoma: ill defined fascicles, diffusely infiltrative, desmin+
● Malignant fibrous histiocytoma: infiltrative, marked pleomorphism and mitotic activity
● Rosai-Dorman disease: CD68+ histiocytes, not storiform

End of Skin / Soft Tissue Tumors > Fibrohistiocytic tumors > Benign fibrous histiocytoma (superficial)

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