Pathological characteristics of a series of rare chronic histiocytic intervillositis of the placenta.

Chronic histiocytic intervillositis of the placenta (CHI) is a rare and poorly understood pathology which may occur in all trimesters. The most conspicuous feature is a histiocytic infiltration of the intervillous space without involvement of the villous parenchyma. In this report on CHI, we re-evaluate a series of four cases and focus on histological, immunohistological and fluorescence in situ hybridisation-derived findings, fetal status and clinical data for previously unrecognised CHI-associated features. Our approach revealed that assisted reproduction-induced pregnancy had been performed in 2 of 4 CHI cases, but other factors and comorbidities are likely to contribute to CHI.