To the Editors:
Dermatofibroma is the most common benign lesion of the skin. Histopathologically, it is characterized by epidermal changes, including hyperkeratosis, acanthosis, basal layer hyperpigmentation, and dermal lesion composed of macrophages, fibroblast-like cells, and vessels.1 There are various histological variants, reflecting the predominant components.1 The most common subtype is a fibrocollagenous variant, followed by histiocytic, aneurysmal, angiomatous, sclerotic, monster, palisading, keloidal, and lipidized variants.2 Lipidized fibrous histiocytoma is one of the variants of fibrous histiocytoma, characterized by accumulation of predominant foamy macrophages and surrounding sclerotic collagen bundles.1,3 Even though foamy macrophages can be observed in a cholesterotic fibrous histiocytoma, it differs from lipidized fibrous histiocytoma. Cholesterotic fibrous histiocytoma is a rare variant, defined as cholesterol deposition within a fibrous histiocytoma.4 To the best of our knowledge, only one case of cholesterotic fibrous histiocytoma has been reported in the literature.4 We present a rare case of a patient diagnosed with cholesterotic fibrous histiocytoma.
A 39-year-old man was referred to our institution with a several-year history of a brownish papule on the right postaxillary line (Figs. 1A, B). Skin examination showed a solitary, 5-mm, brownish, oval-shaped, hard papule on the right postaxillary line. There was no history of a preceding event in the area of the lesion, including trauma, surgery, or arthropod bites. The patient did not report any symptoms associated with the skin lesion. Physical examination did not reveal any other remarkable findings except for the skin lesion. Laboratory examination revealed slightly elevated serum triglycerides (188 mg/dL) and low-density lipoproteins (174 mg/dL). Other routine laboratory findings, including complete blood cell count, chemistry, and urinalysis, were within normal limits. He was diagnosed with type 2 hyperlipidemia 3 years before, and treatment with lipid-lowering medication was attempted, but the patient stopped intentionally. An excisional biopsy was performed of the lesion.
Histopathologic examination of the lesion from the right postaxillary line revealed acanthotic epidermis, hyperpigmentation of the basal cell layer, and an ill-defined dermal lesion. The lesion contained numerous, foamy, lipid-laden macrophages surrounded by abundant, almost keloidal, sclerotic collagen bundles and unique cholesterol clefts in the center of the lesion (Fig. 2A). The numerous cholesterol clefts were surrounded by predominant foamy macrophages, and the sizes of the foamy macrophages were variable depending on the extent of intracytoplasmic lipid accumulation. Foamy macrophages were large cells with pale, foamy cytoplasm and small, central vesicular nucleus (Fig. 2B).
We diagnosed this case as a cholesterotic fibrous histiocytoma.
According to Jun and Fletcher,3 lipidized fibrous histiocytoma is a rare variant of fibrous histiocytoma, occurring mostly between the fifth and sixth decades with a man to woman ratio of 2.7:1. This is in contrast to ordinary fibrous histiocytoma, which presents chiefly in women in the fourth and fifth decades of life. About 81% of the lesions develop below the knee, especially around the ankle and is therefore referred to as an ankle-type fibrous histiocytoma.1,3 Lipidized fibrous histiocytomas are usually yellowish polypoid lesions that have a median size of about 2.5 cm, which are larger than an ordinary fibrous histiocytoma (usually less than 1 cm).3 Even though histological findings include accumulation of numerous foam cells, the association between lipidized fibrous histiocytoma and hyperlipidemia has not been established. Jun and Fletcher3 described 22 cases of lipidized fibrous histiocytomas and reported that 2 cases were associated with hyperlipidemia, but these were thought to be incidental.3 Both lipidized fibrous histiocytoma and cholesterotic fibrous histiocytoma are composed of variable degrees of foamy macrophages, but lipidized fibrous histiocytoma differs from cholesterotic fibrous histiocytoma, which is defined as cholesterol deposition within the center of the lesion.
Cholesterotic fibrous histiocytoma has been rarely reported in the literature. For the first time in 1943, Arnold and Tilden5 reported 27 cases of histiocytoma cutis, and 1 case among them revealed microscopic crystals, which were doubtful for cholesterol. Cholesterotic fibrous histiocytoma was first described by Steven et al6 (1990) in a 63-year-old woman with type 2 hyperlipidemia.4 The sizes of the 2 skin lesions were 1.0 and 1.4 cm, and the firm nodules revealed fibrotic yellowish cut surfaces. Histopathologic examination showed common features of fibrous histiocytoma, including acanthosis, basal layer hyperpigmentation, and dermal lesion containing a mixture of fibroblastic and epithelioid cells. Prominent foamy macrophages and unique cholesterol clefts were also present in the middle of the lesion, which sometimes coalesced.4 Following this report, to our knowledge, there have not been any additional cases reported until now.
The exact pathogenesis of the accumulation of cholesterol clefts in the setting of the hyperlipidemia is not fully understood, but the mechanism is thought to involve lipoproteins in the serum leaking from dermal capillaries, then dermal macrophages phagocytosing lipoproteins, and accumulated lipid materials in the cytoplasm forming cholesterol crystals. This process may be facilitated by local trauma through vascular leakage of lipoproteins.
Cholesterol clefts can be seen in other skin diseases such as necrobiosis lipoidica and necrobiotic xanthogranuloma with paraproteinemia.7–9 Necrobiosis lipoidica exhibits granulomatous inflammation, collagen degeneration, and scattered macrophages and giant cells. Cholesterol clefts in necrobiosis lipoidica are unusual findings, and 4 cases have been reported.7,8 Necrobiotic xanthogranuloma shows typical infiltrates of macrophages, foamy cells, Touton-type giant cells, lymphoid nodules, and extensive necrobiosis.9 In a histopathologic study of 22 cases of necrobiotic xanthogranuloma with paraproteinemia, 18 cases revealed cholesterol clefts.9
Cholesterol granuloma (cholesteatoma) can be confused with cholesterol clefts in cholesterotic fibrous histiocytoma, but cholesterol granuloma (cholesteatoma) is thought to arise from degenerated keratins, erythrocytes, and chronic inflammatory reaction. This is compared with cholesterotic fibrous histiocytoma, in which the origin of lipid materials is thought to come from systemic hyperlipidemia. In addition, the former usually arises in the middle ear and rarely in kidney and pancreas.10–12
Cholesterotic fibrous histiocytoma is a rare disease entity. The underlying pathogenesis has not been clarified, but it is thought to have an association with hyperlipidemia. We present a case of cholesterotic fibrous histiocytoma in this report, which may help elucidate the pathogenesis and extend the understanding of variants of fibrous histiocytomas.
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