epithelioid cell histiocytoma

Definition: Epithelioid cell histiocytoma (ECH), also known as epithelioid fibrous histiocytoma, is a peculiar dermal tumor, which can mimic melanocytic, vascular, epithelial, or other histiocytic lesions. Epithelioid cell histiocytoma is thought to arise from dermal dendrocytes. ECH is a vascular fibrous histiocytoma.

Images

 Epithelioid Cell Histiocytoma: Symmetric, collarette, FXIIIa+ ALK+, ALK rearranged

• https://twitter.com/VishwasParekh/status/705436601011277824
• https://twitter.com/VishwasParekh/status/763355536557498368

Synopsis

 epithelioid cells in dermis
 FXIIIa+ histiocytes

Immunochemistry

 approximately 50% FXIIIa+ histiocytic dendrocytes
 CD34-
 smooth muscle actin-

Localization

 skin
 tongue (lingual epithelioid cell histiocytoma)

Molecular biology

 ALK rearrangement and overexpression (25857825, 25413595)

Histogenesis

 ECHs are speculated to originate from dermal microvascular unit and are composed of 2 primary cell populations: CD34+ primitive fibroblastic dendrocytes and factor XIIIa+ histiocytes.

 ECHs putative pathogenesis entails activation of CD34+ "sentinel" reserve dendrocytes, followed by an influx of histiocytes and mast cells. Juxtacrine communication increases release of wound healing factors; suggesting a reactive etiologic component.

 ECH is a vascular fibrous histiocytoma. The constituent cells appear to arise from the activation of resident microvascular CD34+ dermal fibroblasts and the accumulation of FXIIIa+ dendritic stromal assembly histiocytes.

• The CD34+ cells appear to differentiate toward collagenous fibrocytes in association with histiocytes and mast cells in forming collagenous stroma and vessels.

 ECH is a tumor composed of all requisite cell types consistent with the origin from the dermal microvascular unit.

Differential diagnosis

 pyogenic granuloma
 melanocytic tumors
 vascular tumors
 epithelial tumors
 histiocytic tumors

Epithelioid cell histiocytoma can mimic melanocytic, vascular, epithelial, or other histiocytic lesions.

Prognosis

 Consistent with its benign course, the ECH is managed by local excision, and has an excellent prognosis.

See also

 epithelioid tumors
 dendrocytic tumors
 dermal microvascular unit
 dendritic cells

• dendritic cell subpopulations
  • dermal dendrocytes (FXIIIa+ histiocytic dendrocytes)

References

 ALK rearrangement and overexpression in epithelioid fibrous histiocytoma. Doyle LA, Mariño-Enriquez A, Fletcher CD, Hornick JL. Mod Pathol. 2015 Jul;28(7):904-12. doi : 10.1038/modpathol.2015.49 PMID: 25857825

 Epithelioid cell histiocytoma of the skin with clonal ALK gene rearrangement resulting in VCL-ALK and SQSTM1-ALK gene fusions. Jedrych J, Nikiforova M, Kennedy TF, Ho J. Br J Dermatol. 2015;172(5):1427-9. doi : 10.1111/bjd.13548 PMID: 25413595

 Silverman JS, Glusac EJ. Epithelioid cell histiocytoma—histogenetic and kinetics analysis of dermal microvascular unit dendritic cell subpopulations. J Cutan Pathol. 2003 Aug;30(7):415-22. PMID: 12859738Epithelioid fibrous histiocytoma shares some of the features seen in dermatofibromas, but there usually is a prominent papillary dermis component (classical examples were almost restricted to the papillary dermis).

The tumor has a sharp line of demarcation from the adjacent dermis, and many of the tumor cells have histiocytoid features. These histiocytoid cells vaguely remind me of decidua and, therefore, differ from the foamy histiocytes that are sometimes found in ordinary dermatofibromas.

An epidermal collarette is occasionally seen in the more protuberant examples. The stroma may be quite vascular, and foci of mucinous stroma are sometimes seen. Some of the cells may have nuclear pseudoinclusions.

Multinucleated cells are sometimes present, but most of these lack the vacant cytoplasmic vacuoles of the type sometimes found in the multinucleated histiocytes of ordinary dermatofibromas.

Mitoses, in my limited experience, are rarely found. There may be foci resembling the spindle cell component of a dermatofibroma.

Many of the cells are factor XIIIa positive, but these factor XIIIa positive cells may not represent the actual tumor cells. Cellular examples that have been restricted to the reticular dermis have been described.

Expansion of the papillary dermis by a population of cells having peculiar histiocytic features is characteristic of the epithelioid cell histiocytoma.

There is often a faint swirling pattern around small blood vessels. Such a pattern vaguely reminds me of decidua. Most of the cells are mononuclear, but a few multinucleated cells may be present. Tissue mucin is sometimes found within the cells.

Intranuclear pseudoinclusions are seen in some preparations, but the cells are S100 negative.

Variants have been described that also involve the reticular dermis and, rarely, there may be foci resembling ordinary dermatofibroma.

Credits

 bweens.com
 bweens.com

Case studies

 histopathology-india.net