Abstract
INTRODUCTION: The prenatal detection of an intrathoracic cyst during the first trimester of pregnancy is an exceedingly rare condition. In this report, we describe a case of first-trimester intrathoracic cyst causing cardiac dextroposition, which resolved by 24 weeks' gestation. CASE REPORT: A 5-mm intrathoracic cyst causing cardiac dextroposition was detected during the routine sonographic scan performed at 12 weeks + 2 days. The cyst remained stable in size until 20 weeks and was no longer identified during focused fetal echocardiography at 24 weeks. DISCUSSION: Our case demonstrates that a first-trimester intrathoracic cyst can have a benign course, either by remaining stable in size or even undergoing complete resolution during the second trimester. A focused sonographic examination should therefore be undertaken as follow-up to determine the final prognosis of these lesions. CONCLUSION: The etiology of intrathoracic cysts detected in the first trimester is unclear and could represent a resolving pericardial cyst.