Brachiocephalic vein occlusion in this case appears chronic given the distension of the hemiazygos-azygos collateral return.

Veins are thought to be the least radiosensitive of the all the blood vessels but cases of superior vena cava obstruction secondary to radiotherapy-induced fibrosis have been reported, which is the most likely etiology in this case as the patient has a history of radiation therapy for breast cancer.