PET in Differentiation of Recurrent Brain Tumor from Radiation Injury*

MR and PET scans of 50-y-old man, with a history of grade 2 right frontal oligodendroglioma, who presented with headaches and memory loss. (A) GdDTPA T1-weighted (Tr = 700, TE = 16) MR scan of 50-y-old man, showing an area of low signal in the right parietal lobe with predominantly peripheral contrast enhancement, edema, and focal areas of hemorrhage, which indicated the possibility of tumor or DLRI. (B) PET scan of patient's brain, showing hypometabolic right frontoparietal area consistent with changes after surgery and radiation. No hypermetabolic foci to suggest recurrent tumor. Tumor was resected on September 8, 1993, and treated with radiation therapy to the frontal and parietal lobes (total dose between September 29 and November 9, 1993 = 56 Gy). Patient continued to have mild cognitive deficits and psychosis. In 1995, patient developed new neurologic deficits and dementia worsened. MR showed progression of edema and enhancement in the right parietal lobe, next to the resection site. PET scan in November 1995 was negative for abnormal hypermetabolic foci; a second craniotomy was performed December 1995, and right frontoparietal cystic lesion without evidence of malignancy on a frozen section was removed. Histologic examination showed mixed astrocytoma and oligodendroglioma without mitotic activity, and with areas of focal necrosis. Patient died in February 1996.