Enterovirus Placentitis is an Underrecognized Cause of Placental Pathology

The placenta is susceptible to infection by a number of viral pathogens, including severe acute respiratory syndrome coronavirus 2, which is associated with poor fetal outcomes. The histologic pattern of injury, termed severe acute respiratory syndrome coronavirus 2 placentitis, is characterized by a triad of increased perivillous fibrin deposition, intervillous histiocytes, and trophoblast necrosis. While the etiology of massive perivillous fibrin deposition (MPVFD) is mostly unknown, previous case reports of MPVFD in association with maternal Enterovirus (ENT) suggest that a subset of these cases are a consequence of undiagnosed viral infection. We evaluated 46 placentas collected between 2011 and 2022 with a diagnosis of MPVFD (n = 41) or chronic histiocytic intervillositis (CHI; n = 4). Combining methods of pan-viral metagenomic sequencing and targeted viral PCR, we detected Enterovirus DNA in 8 of 45 (18%) MPVFD and/or CHI cases. Seven of these positive cases were from MPVFD, and 1 was associated with a CHI diagnosis. Enterovirus A species (n = 7) were commonly identified, whereas one case had Enterovirus B. Histologic evaluation of these cases, including immunohistochemical staining for CD68, demonstrated increased intervillous histiocytes in Enterovirus -positive MPVFD cases in comparison with Enterovirus- negative, as well as evidence of trophoblast necrosis. Thus, we favor the terminology Enterovirus placentitis to describe this pathology. Overall, these findings suggest that Enterovirus is an underrecognized etiology of histologic MPVFD and, possibly, CHI. Further study to evaluate the recurrence risk of Enterovirus placentitis in comparison to MPVFD may help inform future fertility planning in patients with these diagnoses.