Thymic involution in pregnancy: a universal finding?

The thymus is a lymphatic organ that plays a vital role in the development of immunity in childhood. The thymus involutes during periods of stress and may acutely decrease in size but usually recovers to its normal size. The thymus also involutes during pregnancy, a process that is possibly hormonally mediated and thought to be necessary for fetal survival. This report describes two pregnant patients with signs and symptoms suggestive of pulmonary embolism who were incidentally found to have thymic enlargement on computed tomography. Follow-up imaging postpartum in both cases demonstrates a significant reduction in thymus size, suggesting thymic hyperplasia. Both patients delivered healthy babies at term. Thymic involution does not universally occur in pregnancy, challenging the theory of its necessity to fetal survival.