Objective: Complete placental abruption results rapidly in fetal death through acute asphyxia, and identification of thymic lesions at autopsy may help in confirming this diagnosis. Thymic petechiae are a marker for acute asphyxia, while absence of histologically identifiable acute thymic involution (ATI), which requires several hours to develop, may help in exclusion.
Methods: We identified autopsies on 17 3rd trimester stillborns with clinical abruption; 58 stillborns with unexplained demise comprised the control group. Eighty-nine percent of the mothers were African-American. ATI was graded 0-4 (grades 0-1 and 3-4 were combined for analysis), and thymic petechiae were recorded.
Results: In the abruption group, ATI grade 0-1 was more frequent than higher grades: 13 (77%) had ATI grade 0-1 compared to 1 (6%) with ATI grade 3-4 (p < 0.001). In contrast, in the control group, ATI grade 3-4 was more frequent than lower grades: 9 (16%) had ATI grade 0-1 compared to 30 (52%) with ATI grade 3-4 (p < 0.001). Thymic petechiae were more frequent in the abruption compared to control group [10 (59%) versus 2 (3%)] (p < 0.001), and were frequently seen with low ATI grade: 10 (83%) had ATI grade 0-1 (p < 0.001).
Conclusions: The presence of thymic petechiae and ATI grade 0-1 correlates significantly with a clinical diagnosis of placental abruption.
Keywords: Acute thymic involution; fetal autopsy; intrathoracic petechiae; placental abruption; stillbirth; thymic petechiae.