Isolated left common carotid artery connected to the pulmonary artery: where was the arterial duct?

A three-year-old boy was referred for persistent arterial duct. Transthoracic echocardiography showed a right aortic arch and an unusual Doppler flow in the arch vessels and the pulmonary artery. The tomodensitometry showed a right-sided aortic arch, with successive origin of the right common carotid, the right subclavian artery, and an aberrant (lusoria) left subclavian artery. The left common carotid took origin from the pulmonary trunk. During surgery, a fibrous cord independent from the anomaly was identified. An end-to-side anastomosis between the left carotid and the ascending aorta was done and the fibrous cord was divided. Was this fibrous cord a ductal ligament?