Tumor Recurrence or Radionecrosis: A Clinical Dilemma in Long-Term Survivors of Low-Grade Diffuse Glioma With Drug-Resistant Epilepsy

Low-grade diffuse gliomas with isocitrate dehydrogenase (IDH) mutations predominantly affect young adults and are frequently associated with prolonged survival, requiring extended neuro-oncological follow-up. In these patients, differentiating tumor recurrence from radionecrosis after radiotherapy remains a major diagnostic challenge because both entities may present with overlapping clinical manifestations and conventional imaging findings. We present the case of a 35-year-old man with an IDH-mutant grade 2 astrocytoma located in the left temporo-parieto-insular region who underwent subtotal surgical resection followed by radiotherapy and adjuvant temozolomide. During follow-up, he developed focal drug-resistant structural epilepsy with progressive seizure burden despite multiple antiseizure medications. Serial MRI demonstrated the appearance and interval growth of a nodular enhancing lesion within the frontal operculum adjacent to the surgical cavity, raising concern for tumor recurrence. Given the diagnostic uncertainty, 18F-fluoroethyl-L-tyrosine positron emission tomography (18F-FET PET) was performed, demonstrating mild and homogeneous amino acid uptake with a tumor-to-background ratio (TBR) of 1.7 and maximum standardized uptake value (SUVmax) of 2.1, findings favoring treatment-related changes and radionecrosis rather than active tumor progression. Considering the imaging characteristics, eloquent cortical location, and multidisciplinary assessment, a conservative neuro-oncological management approach was favored. This case highlights the importance of integrating advanced metabolic imaging techniques such as 18F-FET PET into the evaluation of long-term survivors of low-grade gliomas (LGGs) presenting with worsening epilepsy and new enhancing lesions after radiotherapy. Amino acid PET imaging may represent a valuable complementary tool for distinguishing radionecrosis from recurrent tumor activity in complex neuro-oncological cases.