Dermatofibroma (fibrous histiocytoma) pathology | DermNet (2023)

Introduction

dermatofibromais a commonbenigno tumoralso known as fibrous histiocytoma. There is debate as to whether dermatofibroma has a reactive orneoplasticorigin. the clinicianinjuryit's a firm tannoduleit is most commonly found on the legs. a number ofhistologicalthere are variants.

Histologyde dermatofibroma

Los dermatofibromas sondermal tumorscharacterized by an ill-definedproliferationof fibrohistiocytic cells within thedermiswith an overlapborder zonesavings account (figure 1). At the periphery of the lesion, there is entrapment ofcollagen(Figure 2). the overlyingepidermismay be acanthotic with magnificationbasalcapa pigmentation. sometimes there isbasaloide inductionof the epidermis (figure 1, arrow) which may resemble small basal cellscarcinomathe benignfolliculartumors

Several histologic variants of dermatofibroma are described below. Please note that not all variants are mutually exclusive and more than one type may be present in the same lesion. Therefore, these variants probably only describe unusual features of dermatofibroma rather than distinct pathologies. That said, understanding these variants is useful to the clinician, as certain features suggest a more aggressive clinical course and therefore require special care, for example, to ensureexcisionmargins and consideration of ongoing monitoring.

The term fibrous histiocytoma can be used interchangeably with dermatofibroma or to describe a dermatofibroma with a prominent storiform pattern.

Mobile phonedermatofibroma

Compared with the usual dermatofibroma, cellular dermatofibroma has a higher chance ofreappearanceafter the split andmetastasisis reported.histologically, there is increased cellularity with a storiform spiral pattern (figures 3, 4).Peripheralcollagen entrapment is less prominent in this variant. there may be an increasemitosisand extension tosubcutaneousfats, which are associated with more aggressive behavior. Approximately 10% of cases havenecrosis.

Cellular dermatofibroma may resemble dermatofibrosarcoma protuberans, which may bedifferentiateddue to its larger size, increased mitosis and marked involvement of thesubcutaneous. CD34 is positive in dermatofibrosarcoma protuberans and generally negative in dermatofibroma, although the cellular variant may havefocalpositivity, mainly in the periphery of the lesion. a study ofclone karyotype abnormalitiesin the dermatofibromas found, cellular dermatofibromas were more likely to have karyotypic abnormalities than common dermatofibromas.

epithelioiddermatofibroma

Epithelioid dermatofibroma is a well-known variant of dermatofibroma that can be confused with other benign dermatofibromas andmalignantmesenchymalinjuries. The recent discovery of common ALK-1translocationit has led some authorities to believe that it is better considered a distinct entity rather than a form of dermatofibroma. Clinically, it is distinct and presents as a red polypoid nodule. Like common dermatofibromas, epithelioid dermatofibromas are most often found on the leg. However, they can be found in unusual places, including the tongue.

Sections through the epithelioid dermatofibroma show a central location,circumscribedunderlying tumorepidermalneck. The tumor is composed of cells arranged in sheets and sometimes in a storiform pattern. Single cells show epithelioidmorphologywith abundanteosinophilic cytoplasmwith roundvesicular coresand prominent nucleoli (figures 5, 6). The cells may be markedly enlarged and exhibit somenuclear atypiaand mitosis. There is often an associationinflammatoryshe was wholeinfiltratedwhich can be useful for diagnosis.

Differential diagnosisincludes other epithelioid tumors:

• amelanotic melanoma- similar grandeepithelioid cellsbut usually shows morepleomorphismoand epidermal involvement, and is S100 positive.
• epithelioidsarcoma—granuloma-like clusters with necrosis, more atypia,curb+.
• Other epithelioid dermal tumors: Immunohistochemical studies may help to exclude epithelioidsvascular, smooth muscle andhistiocíticotumors

aneurysmal dermatofibroma

The clinical presentation of an aneurysmal dermatofibroma is a rapidly growing bluish-brown nodule. The periods of rapid growth are secondary tohemorrhagein the injury. These tumors have a high recurrence rate and there are reports of aneurysmal dermatofibroma withsapHeinvolvement.

Histologically there isopening-ashemorrhagicspaces within the center of the aneurysmal dermatofibroma that mimic vessels but lackendothelialresin. The tumor itself tends to be quite cellular (figure 7, 8).as hemosider declarationIt can be an additional resource. Aneurysmal dermatofibroma can be confused with a vascular tumor; however, diagnostic clues include surrounding features of the dermatofibroma, and endothelial cell markers are positive only in normal vessels and not in aneurysmal spaces.

Atypicaldermatofibroma

Atypical dermatofibroma is also known as monster cell dermatofibroma or pseudosarcomatous dermatofibroma. There are focal areas within a common dermatofibroma that consist of largepolymorphocells with large nucleoli (“monster cells”) (figures 9, 10).

Atypical dermatofibroma can be aggressive with rare reports of metastasis and death. However, many of these cases were described before modern immunohistochemical studies were available and can now be reclassified assarcomas.

Dermatofibroma hemosiderótico

Hemosiderotic dermatofibroma may show extensive deposition of hemosiderin (Figure 11). Clinically, they can bepigmentedand can mimic melanoma.

dermatofibroma lipidizado

Lipidized dermatofibroma is also known as “ankle” type dermatofibroma due to apredilectionto the bottom of the leg. Histologically foamyhistiocitospredominate with marked hyalinization of collagen, resemblingamyloid(figure 12).

dermatofibroma fibrocolagenoso

Fibrocollagenous dermatofibroma presents a prominent storiform or spiral pattern, with a predominance of collagen andfibroblasto-like cells (Figures 13, 14). This subtype appears to be more common in rare cases ofdisseminateddermatofibroma seen inimmunocompromisedpatients

clear cell dermatofibroma

Clear cell dermatofibroma has a benign behavior. It is considered by some experts as a separate entity from dermatofibroma, since it has an atypical morphology. Tumor cells have vesicular nuclei without significant atypia (Figure 15). The histologic features of clear cell dermatofibroma overlap with the recently described clear cell mesenchymal.neoplasia, which is characterized by a dermal proliferation of cells with vesicular and clear nucleilatticecytoplasm with or without cytologic atypia and mitosis.

Deep fibrous histiocytoma

Histologically, deep fibrous histiocytoma resembles dermatofibroma but involves deep subcutaneous tissue orsoft fabrics(figure 16). The extremities are the most common site, followed by the head and neck, and then the trunk. Up to one in five deep fibrous histiocytomasappealafter excision and there are 2 reported cases of metastasis and death.

The hallmark histologic features of deep fibrous histiocytoma include adiffusestoriform pattern and changes similar to hemangiopericytoma with thin-walled branching vessels resembling stag antlers in 40% of lesions. Differentcutaneousdermatofibroma, these lesions are usually CD34 positive.

Special studies of dermatofibroma

Positive immunohistochemistry for Factor XIIIa.

CD34 is usually negative in dermatofibroma, but highlights mixed vessels and may be focally positive at the periphery of the lesion in the cellular variant (Figure 17). Factor 13A usually stains thelesionalcells (figure 18). There is variable positivity for CD68 and smooth muscle actin. An epithelioid fibrous histiocytoma is usually ALK-1 positive.

palisade dermatofibroma

Palisade dermatofibroma is characterized by prominent palisade nuclei, which mimic the Verocay bodies seen in schwannoma. Characteristics differentiated fromschwannomathey include the lack of a capsule and staining for S100 is negative (S100 is positive in schwannoma) (Figures 19, 20, 21).

atrophicdermatofibroma

Atrophic dermatofibroma likely represents the final stage of a dermatofibroma and often presents clinically as a depressed lesion. Histologically, tumor cells are sparsely distributed among abundanthyalinizedcollagen