Radiation Vasculopathy

Abstract

Cerebrovascular radiation related vasculopathies can involve vessels of all sizes. Of these, extracranial Carotid and Vertebral Artery radiation induced atherosclerosis are the most commonly encountered radiation vasculopathy in Asia. This is because of the high incidence of oro-naso-pharyngeal 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. Studies with Doppler measured Carotid Intima Media Thickness have shown up to 21 fold increase in thickness at 1year over the irradiated arteries, and also in patients without traditional risk factors. The incidence, cumulative incidence and prevalence of carotid artery stenosis (CAS) was higher in irradiated arteries. The risk of developing CAS after RT was 4 times higher, with a higher incidence of CAS observed for every category of stenosis. Meta-analyses revealed a high cumulative incidence of CAS, with a nearly doubling of incidence during the first 3 years of follow up. Radiation associated atherosclerotic disease frequently involved both the Common Carotid Artery (CCA) and Internal Carotid Artery (ICA). Radiation plaques were more likely to be diffuse, and tandem plaques causing >50% stenoses were twice as common. Radiation plaques also had more high-risk features, they were more likely to be non-calcified, echolucent, ulcerated, mobile and have intraplaque hypoechoic foci. There was a significant increase in risk of both ischemic and hemorrhagic strokes, highest amongst patients younger than 40 years old. Risk factors for radiation associated atherosclerosis (RAA) include the method of delivery of RT, total dosage used, field of radiation, and time interval after RT. Complications include carotid blowout syndrome with a reported incidence of 3%-4.4%. Soft tissue necrosis, locally recurrent cancer, mucocutaneous fistulas, local infections, exposed clivus on nasoendoscopic examination and skull base erosion on imaging studies predicted for Carotid blowout. Both Carotid endarterectomy and Carotid Artery Stenting (CASt) have been performed but CASt was preferred due to a "hostile neck" from underlying radiation dermopathy and fibrosis, and scarring from prior surgeries. It has been proposed that screening could start as early as 1 year post-RT in higher risk patients, with repeat scans every 3- 5 years, using the non invasive and less expensive Doppler scan. Other radiation related vasculopathies, intracranial aneurysms, intracranial disease or Moyamoya syndrome, cavernomas and microbleeds were less common, and rarely encountered in Asian populations.