Radiation Necrosis

Radiation necrosis is not an infrequent complication of nasopharyngeal, sinonasal, and skull base neoplasms treated with irradiation.144–149,170 Due to the field covered, the temporal lobes are most commonly affected ( Fig. 3.25A,B ), followed by the frontal lobes. The total dose, duration, and fractionation of radiation play an important role in the development of radiation necrosis.149,171 The incidence of radiation necrosis following the treatment of head and neck cancer and skull base neoplasms ranges from 3 to 10%.149,171,172 However, radiation necrosis is probably more common than reported, as many patients are asymptomatic and therefore are not imaged leading to underdetection. Irradiation can also result in radiation vasculitis affecting the deep perforating arteries leading to ischemic sequela in the basal ganglia, thalami, brainstem, and the deep white matter. Symptoms of radiation arteritis are dependent on the regions of the brain affected and may include changes in mental status, focal neurologic deficits, and occasionally, seizures.

Changes in the brain due to radiation necrosis may occur early (during therapy) or be delayed. Delayed radiation changes can be further divided into early (within 3 to 4 months of therapy) and late (months to years following therapy). In early as well as early delayed injury, MRI typically shows T2 hyperintensity representing edema that is frequently reversible.172,173 Late delayed injury is usually related to vascular injury, demyelination, and inflammatory infiltrates. This is characterized on MRI by T2 hyperintensity, mass effect, and enhancement that may be solid or ringlike (peripheral enhancement around a necrotic cavity) ( Fig. 3.25A,B ).172,173 In burnt out radiation necrosis, there frequently is temporal lobe encephalomalacia. Although the differential diagnosis of radiation necrosis includes meta-static disease, in the setting of primary head and neck or skull base malignancies, cerebral metastases are relatively uncommon. Intracranial extension of these neoplasms usually presents with extra-axial (extracerebral) masses, whereas the changes of radiation necrosis are intracerebral.