Cerebral radiation necrosis with accumulation of thallium 201 on single-photon emission CT

A patient who had previously undergone resection of a malignant glioma followed by radiation therapy was found to have a focus of a high accumulation of thallous chloride Tl 201 on single-photon emission CT scans, suggesting recurrent tumor. Resection of this area was performed and the specimen showed radiation necrosis, including such reactive changes as reactive astrocytes and lymphocytes in the necrotic tissue. This case illustrates a diagnostic pitfall in the use of 201Tl single-photon emission CT for distinguishing radiation necrosis from recurrent tumor in patients treated for malignant glioma.