This lesion is also discussed as intraepidermal acrospiroma and as intraepidermal eccrine poroma in some texts.

Hidroacanthoma simplex is composed of the same type of cells (acrosyringeal) that constitute eccrine poromas and dermal duct tumors. This population of small epithelial cells has a monotonous appearance in most areas. Therefore, HAS can be considered an architectural variant of this class of tumors. Duct differentiation and/or 'necrosis en masse' is/are uncommon but very helpful diagnostically when present. Cytologic atypia of the type noted in the intraepidermal component of a porocarcinoma is absent, and carcinoembryonic antigen studies have been reported as being negative. Hidroacanthoma simplex can be readily confused with clonal seborrheic keratosis..
 

	Scan power view. The lesion lacks the type of protrusion into the dermis that would be expected in an eccrine poroma.
	Low power view of area in the black rectangle. The acrosyringeal type cells are sharply demarcated from the adjacent keratinocytes.
	High power view of above. The large nuclear remnants in this field are of the type that can be seen in 'necrosis en masse' of other acrosyringeal tumors. This is a more reliable indicator of eccrine differentiation when seen in the interior of a tumor than when seen on the surface. Such a finding on the surface can sometimes be seen in seborrheic keratoses.
	Low power view of the area in the red rectangle.
	High power view of above. There are no transitional forms between the acrosyringeal cells (left side of picture) of the tumor and the adjacent epidermis in this field.
	Medium power view of the area in the yellow rectangle.
	High power view of above. Another illustration of the contrast beween the acrosyringeal cells of HAS and the adjacent epidermis.

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