Differentiation between recurrent tumor and radiation necrosis in a child with anaplastic ependymoma after chemotherapy and radiation therapy

In patients after treatment for malignant brain tumors, a clear distinction between tumor recurrence and radiation necrosis can be challenging. This case report describes the diagnostic workup in a child with anaplastic ependymoma and inconclusive MRI (magnetic resonance imaging) and PET (positron emission tomography) findings. 1.5 years after resection, hyperfractionated radiotherapy and chemotherapy of an anaplastic ependymoma in the right parietal region, the cranial MRI of an 11-year-old girl showed multiple small contrast-enhanced lesions in the frontal cortex. In the following months, these lesions increased in number and size and neurologic symptoms developed. Diagnostic workup included repeated MRI scans, PET with an (18)F-amino acid and (18)F-fluorodeoxyglucose (FDG), as well as a brain biopsy. Amino acid PET, performed when the lesions were still small, showed multiple small areas of mild uptake in close correlation to the MRI lesions. Although not typical, this result was suspicious of tumor seeding, the more since the lesions appeared in gray matter areas outside the high-dose-rate irradiation field. A biopsy, performed 6 months later when the clinical appearance worsened, showed no tumor tissue. FDG PET, performed after the size and number of the lesions had increased, showed no intensely increased glucose metabolism, a high-grade recurrent tumor was therefore very unlikely. In the following months, the clinical picture stabilized. The final interpretation of the lesions was multiple focal radiation necrosis based on perfusion abnormalities after chemotherapy and conformal hyperfractionated radiotherapy, probably due to an individually enhanced vulnerability of the cerebral vessels.