Rupture of a mediastinal collateral aneurysm associated with unilateral absence of pulmonary artery

Isolated unilateral absence of pulmonary artery is a rare congenital malformation and often asymptomatic in adults. However, aneurysm formation in the aortopulmonary collateral vessels carries a potential risk of life-threatening hemorrhage. This case report describes a 79-year-old woman who presented with rupture of a mediastinal collateral aneurysm associated with isolated unilateral absence of pulmonary artery. We discuss the clinical course, including vascular morphology changes, and subsequent endovascular treatment. Notably, this case demonstrates the rupture of a de novo collateral aneurysm rather than a preexisting one.