CONTRIBUTION TO THE PATHOGENESIS OF RADIATION-INDUCED INJURY TO LARGEARTERIES

We report a case of a 35-year-old man who died of a brain Infarct 20 m onths after radiotherapy for carcinoma of the tonsil with metastases t o the cervical lymph nodes. Histology revealed mild atherosclerosis, n ecrotizing vasculitis, and occlusive thrombosis of the internal caroti d artery. Significant changes were observed in the vasa vasorum: swell ing and detachment of the endothelium, subendothelial oedema, hyaline change, fibrinoid necrosis of the vessel walls with mononuclear cellul ar infiltration, accompanied by focal haemorrhages and chronic inflamm ation in the periadventitial soft tissue. We believe that these change s of the vasa vasorum and necrotizing vasculitis are causally related and that vasculitis represents focal ischaemic necroses with inflammat ory reaction. Our findings support the hypothesis. based on experiment al 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 periadvenlitial tissue from the early lesions described in our patien t, to late stages resulting in dense periadventitial fibrosis as repor ted previously. We suggest that injury to the vasa vasorum and the con sequent ischaemic lesions of the arterial wall are morphological featu res distinguishing radiation-induced arterial injury from spontaneous atherosclerosis.