Abnormal placental membrane morphology Chronic villitis 2021-01-22T12:38:39Z Villitis of unknown aetiology Villitis of unknown etiology Villitis of unknown etiology (synonymous with villitis of unknown etiology) is a histologic diagnosis and, although it may have a variable distribution, evidence indicates that 3 parenchymal blocks will identify 62% of villitis, reaching an asymptote of 6 and 7 blocks identifying 85% of villitis. Villitis of unknown etiology by definition excludes those cases where an etiology is identified, such as viral or acute infections, and thus is preferred to the term nonspecific chronic villitis. It is usually lymphohistiocytic: although the presence of rare plasma cells does not exclude the diagnosis, thorough evaluation for an infectious etiology, such as cytomegalovirus, is required in a predominantly plasma cell villitis. Nonspecific chronic villitis Chronic villitis (non-infectious)