At some point in the disease, most patients with low-grade gliomas (astrocytoma, oligodendroglioma, or mixed oligodendroglioma) are likely to present with progressively more severe neurologic signs and symptoms with neurologic imaging changes associated with tumor recurrence. These imaging changes include the appearance of new foci of enhancement and increasing brain edema. Although it is difficult to distinguish tumor recurrence from radiation necrosis from clinical presentation and imaging features, PET, SPECT, or MRS examinations can help to differentiate the two. To clarify the differential diagnosis, tissue specimens need to be obtained. An analysis of the surgical database: 100 patients with suspected low-grade astrocytoma recurrence underwent reoperation, and pathology showed 33% low-grade tumors, 64% high-grade tumors and 3% radiation necrosis. In a study by Forsyth et al. 51 patients (40 of whom had Kernohan grade 1 or 2 astrocytoma, oligodendroglioma, or oligodendroglioma) previously treated with radiation therapy underwent stereotactic tissue biopsy for suspected tumor recurrence. Pathology revealed tumor recurrence in 30 cases (59%), tumor recurrence plus necrosis in 17 cases (33%), pure radiation necrosis in 3 cases (6%), and radiation-induced sarcoma in 1 case (3%). Of the recurrent tumors found on biopsy, 63% were high-grade gliomas. The median survival time for patients with biopsy-detected tumor recurrence was 10 months after biopsy, while the median survival time for patients with biopsy-detected tumor recurrence and radiation necrosis was 22 months after biopsy, the former being significantly worse than the latter. The three patients whose biopsies showed pure radionecrosis did not die. In conclusion, survival after tumor recurrence would be decreased. The median survival time for patients who developed tumor progression after surgery and radiotherapy was 9.7 months, with a 2-year survival rate of 29%, as reported in one study series. However, specific pathological findings at the time of biopsy or reoperation clearly affect patient prognosis. For example, Leighton et al. reported a median survival of 39 months for all patients with recurrent tumors, 16 months for recurrent low-grade astrocytomas, and 60 months for recurrent low-grade oligodendrogliomas. Treatment of recurrent tumors includes surgery, external radiotherapy, intertissue brachytherapy, and chemotherapy. For patients who have been followed up and treated with surgery only, reoperative treatment and postoperative radiotherapy are available if tumor progression occurs. The advantage of reoperation is that the pathologic diagnosis and grade of recurrent tumor can be clarified. The pathologic grade of the recurrent tumor is a guide to the use of further therapeutic measures. Patients who progress from low-grade to high-grade glioma have a better prognosis with further surgery and radiotherapy than those who started with high-grade glioma. For recurrent tumors that have already received external radiation therapy, stereotactic radiosurgery or stereotactic radiotherapy may be used depending on the size and location of the tumor. Patients treated repeatedly are at higher risk of radiation necrosis or hormone dependence. In addition, further chemotherapy is an optional treatment.