Radiation Vasculopathy

Cerebrovascular radiation-related vasculopathies can involve vessels of all sizes. Of these, extracranial carotid and vertebral artery (VA) radiation-induced atherosclerosis are the most commonly encountered radiation vasculopathy in Asia. This is because of the high incidence of oro-nasopharyngeal cancers in this region, where radiation therapy (RT) is the mainstay treatment.

Radiation exposure induces the early and rapid development of atherosclerosis in the extracranial arteries. In retrospective studies, significant changes were demonstrated as early as 1 year after RT, using carotid intima media thickness measurements. Plaque development continued at an accelerated rate, with a four times increased risk compared to those without radiation exposure, and regardless of the presence or absence of traditional risk factors. In addition, radiation-induced plaques were often extensive, involving all cranial arteries exposed to radiation. They often have high-risk features, which included echolucent plaques with ulcerations, mobile components, and/or intraplaque hypoechoic foci. The risk of both ischaemic and haemorrhagic strokes are increased, with the highest risk seen in patients younger than 40 years old. Carotid blowout is a rare and potentially deadly complication, which could involve the common, internal or external carotid arteries. Both carotid endarterectomy and carotid artery stenting have been performed, but there is a preference for stenting because of a "hostile neck," from underlying radiation dermopathy and fibrosis, or scarring from prior surgeries, both contributing to poor wound healing and difficult CEA. Favourable outcomes have been reported with transcarotid artery revascularisation, compared against CEA. Other radiation-related vasculopathies, intracranial aneurysms, intracranial disease or moyamoya syndrome, cavernomas, and microbleeds were less common and rarely encountered in Asian populations. Of this, radiation-related intracranial aneurysm has been described in <1% of Chinese patients who had head and neck radiation, with a long latency periods after radiation exposure, ranging from median lag time of 6-20 years.

Cerebrovascular radiation vasculopathies have a diverse phenotypic range, from small vessel to large vessel involvement, from extracranial to intracranial disease, intracranial aneurysms, cavernomas and microbleeds. In Asia, extracranial carotid and VA radiation-induced atherosclerosis was most commonly encountered and reported, due to the prevalence of oro-nasopharyngeal cancers in many parts of this region. Complications include atherosclerosis, stroke, and increased risk of carotid blowout syndrome.