Late appearance of a radiodense lesion at the site of an irradiated metastasis: neuropathological findings.

The appearance of contrast-enhancing computed tomographic (CT) lesions at the site of an irradiated brain tumor often has sinister implications. We present the case of a 43-year-old woman who received cranial irradiation as treatment for cerebral metastases from lung cancer. Follow-up radiographic studies revealed complete tumor regression; however, 26 months after treatment, enhanced CT scanning showed a radiodense nodule at the site of one of the previous metastatic deposits. Neuropathological examination of the surgically excised tissue identified benign reactive changes only. The natural history of irradiated brain lesions is discussed.