Lipidized Fibrous Histiocytoma: Differential Diagnosis from Juvenile Xanthogranuloma.

Dear Editor:

Fibrous histiocytoma (FH) is one of the most common benign tumors of the skin and represents a group of mesenchymal lesions with histiocytic, fibroblastic, and myofibroblastic differentiation1. Cutaneous FH has been clinically characterized as a solitary, raised, round, red-brown, and firm nodule measuring about 1 cm in diameter1. It most often occurs on the extremities of young or middle-aged adults and shows a slight female predominance2. Several clinicopathologic variants of FH have been described and include cellular benign FH, aneurysmal FH, epithelioid cell FH, atypical FH, deep penetrating FH, and lipidized FH12.

Lipidized FH is a subtype of FH that is relatively rarely observed, accounting for 2.1% of the variants of FH3. It most commonly develops in the lower limbs, so it has been previously called “ankle-type” FH. In comparison to other variants, it appears clinically as a large exophytic yellow nodule around the ankle3. We herein report a case of an unusual histological variant of FH presenting clinically as a juvenile xanthogranuloma (XG)-like lesion and describe the tumor using histological and immunohistological techniques.

In the current case, a 33-year-old male presented to our hospital with an asymptomatic papule on the left forearm area that had been present for 6 months. Physical examination revealed a single non-tender, erythematous to yellowish-colored, firm, hairless papule that was 5×6 mm in diameter (Fig. 1A). The tumor was completely removed by punch excision. Histopathological examination revealed a dermal tumor that abutted the epidermis and extended into the subcutis (Fig. 1B). Epidermal hyperplasia with hyperkeratosis was present. The tumor was comprised of proliferating histiocytoid cells and fibroblast-like spindle cells in a storiform pattern. Vascular proliferation and sclerotic collagen bundles were noted. High magnification imaging revealed a dense infiltration of numerous foam cells that were oval to polygonal in shape with large hypochromatic nuclei, prominent nucleoli, and abundant vacuolated cytoplasm (Fig. 1C). Binucleated or multinucleated Touton-type giant cells were also present. Immunohistochemical staining was positive for CD68, focally positive for CD34, especially in the peripheral region of the lesion, and negative for S-100 and leukocyte common antigen (Fig. 1D). The foam cells showed diffuse cytoplasmic staining for CD68. Finally, the patient was diagnosed with lipidized FH based on the pattern of histology and immunohistochemistry.

Fig. 1

(A) A solitary asymptomatic, 6-mm-sized, erythematous to yellowish-colored, dome-shaped nodule on the left forearm. (B) The dermal tumor abutted the epidermis and extended into the subcutis (H&E, ×40). (C) A storiform pattern of arranged spindle cells and entrapped collagen bundles was noted (H&E, ×100). (D) The foamy cells showed diffuse cytoplasmic staining with CD68.

Lipidized FH was identified in 1994 as a single exophytic yellowish nodule composed of foamy macrophage that had a predilection for the ankle1. It is a rare and under-recognized variant of FH that needs to be distinguished from juvenile XG1. Juvenile XG is a common benign histiocytic skin tumor that affects preferentially the head and neck of children4. Clinically, it presents as either solitary or multiple, well demarcated, and yellowish to tan nodules measuring several millimeters in diameter4. These two tumor types are compared in Table 1245.

Table 1

Comparison of lipidized fibrous histiocytoma (FH) and juvenile xanthogranuloma (XG)

Characteristic	Lipidized FH	Juvenile XG
Tumor origin	Non-Langerhans histiocytes	Non-Langerhans histiocytes
Clinical findings	A solitary large (median 2.5 cm in diameter), exophytic, yellowish to brownish nodule	A yellowish to tan papulonodule measuring several millimeters in diameter
Histopathological findings	Epidermal hyperplasia with foamy histiocytes, peripheral entrapped dermal collagen fibers, and fibroblast-like spindle cells in a storiform pattern in the deep dermis	A dense proliferation of foamy histiocytes, cytologically bland mononuclear cells, lymphocytes, and Touton giant cells
Lipidized cytoplasm	Weekly lipidized cytoplasm	Heavily lipidized cytoplasm
Immunochemistry	CD68(+), CD34(±), S-100(−), factor XIIIa(±), CD4(−), LCA(−)	CD68(+), CD34(−), S-100(±), factor XIIIa(+), CD4(+), LCA(+)
Preferential site	Lower limbs, especially around the ankle	Head and neck

LCA: leukocyte common antigen.

Lipidized FH is a rare disease that is sometimes clinically misdiagnosed as juvenile XG. In this case, differential diagnosis was challenging, but the histopathology suggested that this lesion was lipidized FH. Therefore, when these two diseases cannot be clearly distinguished, histology and immunohistological techniques may be needed.