Reticulohistiocytoma (Solitary Epithelioid Histiocytoma)

Abstract

Reticulohistiocytoma and multicentric reticulohistiocytosis are designations for uncommon, incompletely characterized histiocytic proliferations of the skin or soft tissues. In this study, we analyzed a uniform group of 44 lesions composed of epithelioid histiocytes, comprising a subset of lesions originally designated as reticulohistiocytoma, and propose designating them as "solitary epithelioid histiocytoma" (SEH), in line with the recently published classification proposal for histiocytic disorders. There were 26 males and 18 females with a median age of 35 years (range, 2.5-74 years). All patients had a superficial, circumscribed, mildly elevated, solitary lesion (size range, 1.5-11 mm; median, 4 mm), located in the trunk wall (n = 16), lower extremity (n = 12), head and neck (n = 8, including 2 in the oral cavity), upper extremity (n = 6), penis (n = 1), and an unspecified site (n = 1). Histologically, the lesions typically involved upper and mid-dermis and were not ulcerated. They were composed of large epithelioid histiocytes with a varying number of lymphocytes and neutrophils. The histiocytes had abundant, typically densely eosinophilic, cytoplasm and mostly mild, if any, nuclear atypia. Multinucleated forms with randomly oriented nuclei were also present. The histiocytes had low mitotic activity (range, 0-4 mitoses per 10 wide HPFs; median, 1 mitosis per 10 HPFs). The lesions contained varying numbers of CD3-positive T cells, whereas B lymphocytes, plasma cells, eosinophils, and mast cells were scant, if present at all. Immunohistochemically, the epithelioid histiocytes were positive for CD163, CD68, lysozyme (variably), and vimentin. They often had focal nuclear immunoreactivity for microphthalmia transcription factor, and they sometimes had focal reactivity for Factor XIIIa and S-100 protein. Membrane positivity for CD31, CD43, and CD45 was variable. The epithelioid histiocytes were consistently negative for CD3, CD20, CD30, HMB45, and keratins. All 12 patients with follow-up information had an uneventful clinical course with no recurrences (median, 13 years). SEH is a benign, probably reactive, histiocytic proliferation of unknown etiology. It needs to be distinguished from Rosai-Dorfman disease, juvenile xanthogranuloma, a variety of granulomatous conditions, and some malignant neoplasms, including histiocytic sarcoma, melanoma, and epithelioid sarcoma.

Neurothekeoma of the Cornea

“…Reticulohystiocytomas (solitary epithelioid histiocytomas) differ from NTK in that they rarely show whorled growth and cytoplasmic retractions with filopod extensions, and rarely demonstrate nuclear atypia. Additionally, they show strong positivity for CD163 and CD68 and, in some cases, focal positivity for S100 [8]. …”

Reticulohistiocytoma of the Orbit

“…1 It is a nonneoplastic entity arising from macrophages rather than dendritic histiocytes. Histologically, RHs are composed of large mononuclear and multinucleated histiocytes with “ground glass” cytoplasm.…”

“…2 In contrast, multicentric reticulohistiocytosis is manifest by multiple nodules 5 and can be differentiated from solitary RH by its association with systemic disease. Sometimes referred to as “lipoid dermatoarthritis,” patients with multicentric reticulohistiocytosis may have arthropathy, 1 and there may be an associated internal malignancy. 6 Both entities occur predominantly in adults.…”

“…Historically, RHs occur in young adults with a slight male predominance. 1 RHs are thought to be nonneoplastic, localized, cytokine-induced collection of histiocytes reacting to an unknown stimulus. 1 …”

“…The histiocytes in this disease are nonLangerhans cells and usually S100 positive. 1 Langerhans cell histiocytosis is a histiocytic disease that occurs in children and commonly presents as a lytic defect affecting the superotemporal orbit or sphenoid wing. 9 In contrast to Rosai-Dorfman disease, Langerhans cell histiocytosis cells bear the Langerhans cell granule (Birbeck granule) and are CD1a and S100 positive.…”