Chorionic vasculitis is the hallmark of a fetal response in chorioamnionitis. There are five highly characteristic findings: (1) leukocyte migration is not concentric but rather radiates toward the infected amniotic fluid; (2) the infiltrate is primarily neutrophils; (3) multiple chorionic vessels, first veins and then arteries, are usually involved; (4) the infiltrate never extends into the vasculature of stem villi; and (5) it is rare in the absence of chorioamnionitis (or its precursors). Here we describe a new form of chorionic vasculitis characterized by an infiltrate composed primarily of eosinophils and CD3+ T lymphocytes that very focally involves a single chorionic vessel (artery or vein), that radiates away from the amniotic fluid (i.e., toward the intervillous spaces), and that may extend into the stem villous vasculature; this lesion occurs in the absence of any evidence of chorioamnionitis. During the past 7+ years, using accepted placental review criteria, we have examined 7104 placentas and identified 14 cases of eosinophilic/T-cell chorionic vasculitis (or related lesions). Although the frequency of diagnosis in the placentas examined was 0.197%, its true incidence cannot be estimated because of its very focal nature and the limited nature of placental disk sampling. Its etiology and significance are unknown, but it may represent a focal immune-mediated vasculitis.
