S8C19bP6b-1: The pattern is that of a well developed vasculitis with prominent fibrinoid necrosis (actually, adventitial deposits of fibrinoid) about vessels in the reticular dermis. The process extends along vessels to the deeper portions of the reticular dermis. The intervening reticular dermis shows mild interstitial infiltrates; these interstitial infiltrates are more prominent, as well as band-like, at the interface between the reticular dermis and the papillary dermis. The papillary dermis is markedly edematous (a common feature of a vasculitis). The epidermis is hyperplastic, but the keratin layer is not altered (a common feature of a vasculitis) (erythema elevatum diutinum).

S8C19bP6b-2: The connective tissue at the interface between the edematous papillary dermis and the reticular dermis is smudgy and necrotic. The infiltrates of neutrophils show leukocytoclasia. The patterns are Sweet’s syndrome-like. In this area in this example, the process takes on a pyodermatous quality (EED).

S8C19bP6b-3: The wall of the vessel is fibrotic and edematous; it contains loose infiltrates of neutrophils. The broad zone of fibrinoid necrosis is mostly representative of an altered vascular adventitia; this pattern, although usually not as extreme as in this example, is a common pattern in the setting of a vasculitis (i.e., the necrosis of a vasculitis often is more prominent in the adventitia of a thin-walled dermal vessel than in the actual wall of the vessel) (EED).