Transient early computed tomographic changes mimicking tumor progression after brain tumor irradiation.

Transient computed tomographic (CT) changes occurring within three months after radiotherapy are described in three patients with cerebral gliomas. These changes consist of enlargement of an area of central necrosis, new tumor enhancement, and increased tumor enhancement with adjacent low-density changes. Subsequent scans showed regression of these changes in all patients. It is proposed that these changes are the direct effect of radiation on tumor tissue and adjacent normal brain; possible mechanisms are discussed. These radiation-induced changes mimic tumor progression on CT. The importance of recognizing their transient nature is stressed.