Umbilical cord ‘pseudo‐vasculitis’ following second trimester fetal death: a clinicopathological and immunohistochemical study of 13 cases

Amniotic fluid bacterial infection is an occasional cause of second trimester septic abortion. We describe an autolysis-related histological artifact, umbilical cord 'pseudo-vasculitis', which can erroneously implicate amniotic bacterial infection in fetal death. Clinicopathological features of 13 second trimester fetal deaths with umbilical cord pseudo-vasculitis are reported. In four cases (31%), an incorrect pathological diagnosis of umbilical vasculitis had initially been rendered. Umbilical cords from five cases of pseudo-vasculitis and one comparison fetus (18-week septic abortion with true umbilical vasculitis), were studied with chloroacetate esterase and with immunohistochemical staining for myeloperoxidase, muscle-specific actin (HHF35) and smooth muscle actin. Histologically, umbilical pseudo-vasculitis exhibited numerous small, rounded, degenerating cells with irregular, multilobed nuclei (closely resembling neutrophils) located within the umbilical vessel wall. Immunohistochemical studies demonstrated that all cells resembling neutrophils were of smooth muscle origin. Moderate to severe fetal autolysis was present in all cases of umbilical pseudo-vasculitis, suggesting that this finding represents autolysis of umbilical vascular smooth muscle secondary to post moderate fetal retention. Vascular smooth muscle in other fetal and placental locations did not demonstrate the finding, suggesting that this striking degenerative artifact of smooth muscle is restricted to the umbilical cord.