Contribution to the pathogenesis of radiation-induced injury to large arteries.

We report a case of a 35-year-old man who died of a brain infarct 20 months after radiotherapy for carcinoma of the tonsil with metastases to the cervical lymph nodes. Histology revealed mild atherosclerosis, necrotizing vasculitis, and occlusive thrombosis of the internal carotid artery. Significant changes were observed in the vasa vasorum: swelling and detachment of the endothelium, subendothelial oedema, hyaline change, fibrinoid necrosis of the vessel walls with mononuclear cellular infiltration, accompanied by focal haemorrhages and chronic inflammation in the periadventitial soft tissue. We believe that these changes of the vasa vasorum and necrotizing vasculitis are causally related and that vasculitis represents focal ischaemic necroses with inflammatory reaction. Our findings support the hypothesis, based on experimental studies, that injury to the vasa vasorum is an important mechanism in the development of radiation-induced vasculopathy of large arteries. They also suggest an evolution of the injury to the vasa vasorum and periadventitial tissue from the early lesions described in our patient, to late stages resulting in dense periadventitial fibrosis as reported previously. We suggest that injury to the vasa vasorum and the consequent ischaemic lesions of the arterial wall are morphological features distinguishing radiation-induced arterial injury from spontaneous atherosclerosis.