Chronic inflammatory conditions of the placenta

Placental inflammatory conditions comprise a main diagnostic category in placental pathology. Placental inflammation can broadly be categorised into acute and chronic, with co-existence of both in the same placenta also possible. Chronic inflammation may be of infectious or non-infectious aetiology. TORCH infections represent the majority of placental infections associated with chronic inflammation in developed countries. Non-infectious chronic placental inflammatory conditions, such as villitis of unknown aetiology (VUE) and chronic histiocytic intervillositis (CHI) are currently attributed to immune-mediated mechanisms and aetiology, and have been associated with significant implications such as miscarriage, stillbirth, premature delivery, intra-uterine growth restriction, poor neurological outcome in living babies, and recurrence risk in future pregnancies. Standardised histologic diagnostic criteria have been proposed for the diagnosis of VUE, whereas a standardised histologic definition is currently lacking for CHI, hampering the comparison between different studies and hindering reaching conclusions about the effectiveness of different treatment strategies. This review will discuss inflammatory conditions of the placenta with emphasis on histopathological diagnosis, clinical associations, and implications for future clinical care.