S2C7aP2a-1: Pityriasis rosea is a spongiotic dermatitis; occasionally, the basal unit hyperplasia is more developed and the lesion has both spongiotic and psoriasiform qualities. In this example, there is mild hyperplasia of the basal unit of the epidermis; focal areas of parakeratosis are associated with the areas of spongiosis in the basal unit of the epidermis. Mild perivascular infiltrates of lymphocytes follow vessels into the dermal papillae; they extend into the epidermis mostly at the tips of dermal papillae. The papillary dermis is widened and edematous. Blue arrows identify an area showing extravasated red blood cells in a dermal papilla and in the overlying epidermis.

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S2C7aP2a-2: The extravasated red blood cells in the epidermis vary in size; some of the cells are fragmented. The basal unit of the epidermis is hyperplastic; spaces among keratinocytes of this unit are widened (spongiosis). The papillary dermis is edematous. To the left of the center of the field, there is peri-vascular edema.

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