epithelioid cell histiocytoma

EPITHELIOID CELL HISTIOCYTOMA (EPITHELIOID BENIGN FIBROUS HISTIOCYTOMA OF SKIN)

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.

From the upper back of a 50 year old female:

	Composite scan power view. The papillary dermis is massively expanded by a relatively uniform population of cells. There is a surface erosion, and there is edema of the upper left side of the lesion. There is an artifactual cleft on the right side.
	A medium power view from the junction of the lesion (upper left) and the reticular dermis (lower right). The line of demarcation is moderately distinct.
	High power view of the cells that constitute the tumor. Note the way they loosely swirl around the blood vessel.
	Another high power view showing features similar to those shown above. The arrow points to a blood vessel (BV).

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