ABSTRACT
<p><b>OBJECTIVE</b>To study the clinicopathologic features of delayed radiation-induced brain injury after radiotherapy for brain tumor.</p><p><b>METHODS</b>The clinical, histopathologic and immunohistochemical features of 9 cases with delayed radiation-induced injury were evaluated.</p><p><b>RESULTS</b>The disease occurred from 6 months to 12 years after radiotherapy and often presented with headache and muscle weakness. Magnetic resonance imaging showed peripheral enhancing lesions with slight mass effect and surrounding edema. Microscopically, the major changes included coagulative necrosis, fibrinoid necrosis of vessels, vascular hyalinization with luminal stenosis and peripheral reactive gliosis. Immunostaining for hypoxia-inducible factors 1α was positive in reactive astrocytes.</p><p><b>CONCLUSIONS</b>Delayed radiation-induced brain injury is a relatively common complication of radiation therapy. The lesion was frequently misdiagnosed as brain tumor. Correct diagnosis relies on clinical, radiologic and pathologic correlation.</p>