Radiation-induced changes in the central nervous system and head and neck.

Radiation therapy of the brain, neck, and spine can be associated with radiation-induced changes that are increasingly evident radiologically. These changes affect the central nervous system (focal necrosis, diffuse white matter injury, atrophy, mineralizing microangiopathy, telangiectasia, optic neuropathy, large vessel vasculopathy), bone (fatty replacement of marrow, osteoradionecrosis, sinus inflammation), and superficial and deep soft tissues and include neoplasia. Focal necrosis, which most commonly occurs at the treatment site, is seen at computed tomography (CT) and magnetic resonance (MR) imaging as a ring-enhancing mass with edema and mass effect, findings similar to those of tumor recurrence. Diffuse white matter injury appears as hypoattenuating (at CT) or hyperintense (at MR imaging) small foci near the frontal or occipital horns or as a confluent band extending from the ventricles to the corticomedullary junction. Fatty replacement of marrow is the most common osseous complication seen on MR images. Osteoradionecrosis, which occurs most often in the mandible, appears as a focal lytic area at CT and with abnormal marrow signal and cortical destruction at MR imaging. The most common changes in the superficial soft tissues of the head and neck, edema and fibrosis, are seen radiologically as skin thickening and increased soft-tissue attenuation with stranding of subcutaneous fat. Meningioma, the most common radiation-induced CNS tumor, can be distinguished from spontaneous meningiomas on the basis of clinical characteristics (eg, presence of focal alopecia and scalp atrophy).