Thoracic Giant Venous Malformation in a Stillbirth with <i>Pik3ca</i> Somatic Mutation

<b>Introduction:</b> Congenital venous malformations (VMs) are typically located in the skin of the head and neck, but extension to deep tissues and visceral organs may occur. In 20% of cases, sporadic VMs are caused by somatic mutations in the <i>PIK3CA</i> gene, which determines aberrant angiogenesis. <b>Case report:</b> Intrauterine death of a fetus with a known extensive vascular lesion of the right hemithorax occurred at 28 weeks + 6 days. Autopsy revealed abundant bilateral pleural effusions, and histology showed a VM. High-depth next-generation sequencing for <i>PIK3CA</i> and <i>TEK</i> on amniocytes was negative. Postmortem real-time polymerase chain reaction for <i>PIK3CA</i> on paraffin-embedded samples of the lesion revealed somatic p.H1047X hotspot mutation in the exon 20. <b>Conclusion:</b> To the best of our knowledge, this is the first case of a VM in a stillbirth. Extensive lesions carry a high risk of fetal demise due to high-output cardiac failure.