SARS-CoV-2 Placentitis: A Review of Pathologic Findings and Discussion of Differential Diagnosis.

CONTEXT.—: Maternal SARS-CoV-2 infection has been associated with increased adverse events in the mother, as well as increased stillbirths (11.5 per 1000), spontaneous abortions, and premature delivery. Clinical symptomatology, or the lack thereof, does not appear to be directly related to fetal or neonatal complications. SARS-CoV-2 placentitis is now recognized as the culprit, and the presence of the virus in the syncytiotrophoblasts of the placenta has emerged as a significant predictor of fetal compromise.

OBJECTIVE.—: To provide a review of the clinical presentation and outcomes, morphologic characteristics, detection methods, and differential diagnosis of SARS-CoV-2 placentitis.

DATA SOURCES.—: A case of placental pathology in a patient with COVID-19 infection at the University of Michigan, as well as a review of the available literature through a search of PubMed and Google Scholar.

CONCLUSIONS.—: SARS-CoV-2 placentitis is a well-documented outcome of symptomatic and asymptomatic COVID-19 infection during pregnancy. It can disrupt placental function and lead to severe outcomes in the neonate, including growth restriction and stillbirths. Chronic histiocytic intervillositis, perivillous fibrin deposition, and trophoblast necrosis, when present together, may act as a morphologic signature of SARS-CoV-2 placentitis. The histologic differential diagnosis includes massive perivillous fibrin deposition (MPFD)/maternal floor infarction (MFI), chronic villitis of unknown origin, or other infectious villitides. Immunohistochemistry and RNA in situ hybridization are specific to the viral antibodies and RNA, respectively, and are essential for classification.