Vieussens' arterial ring forming a coronary-pulmonary artery fistula with large aneurysmal dilatation: a case report.

Background: Vieussens' arterial ring (VAR) is an embryonic conotruncal ring remnant that represents a rare vascular anomaly involving a connection between the right coronary artery (RCA) and the left anterior descending artery (LAD). We describe a unique case of VAR associated with large aneurysmal dilatation, which presents as the formation of a fistula between the coronary artery and pulmonary artery. Case summary: An 80-year-old Japanese woman presented with an asymptomatic mediastinal mass that was incidentally detected on computed tomography. Subsequent imaging over 2 years revealed the progression of the two masses connecting the RCA to the LAD measuring 8 × 7 mm and 28 × 21 mm in diameter. Transthoracic echocardiography identified a cystic lesion anterior to the right ventricular outflow tract, and colour Doppler imaging confirmed flow into the pulmonary artery. Furthermore, coronary angiography revealed a large aneurysm arising from the LAD, with an efferent vessel communicating with the pulmonary artery. Surgical intervention involved resection of the aneurysms and closure of the coronary-pulmonary artery fistula, which yielded favourable postoperative outcomes. Discussion: Vieussens' arterial ring is a rare but clinically significant anomaly with varied presentations; the incidence of VAR remains uncertain. In this case, surgical resection and closure of the fistula were performed to mitigate the risk of rupture and to address the potential haemodynamic consequences. Understanding and documenting such cases will contribute to refining treatment approaches and improving patient care in cardiovascular medicine.