Long-term imaging evolution of an indeterminate hypodense lesion highly suggestive of oligodendroglioma: a case report

Oligodendroglioma is an adult-type diffuse glioma that predominantly affects middle-aged adults and is uncommon in adults aged 80 years or older. Long-term imaging documentation of an indeterminate intracranial lesion before symptomatic tumor progression is rare. An 82-year-old man with hypertension, type 2 diabetes mellitus, and coronary heart disease presented in 2020 with progressive neurological symptoms and marked enlargement of a long-standing right frontal lesion. A right frontal hypodense lesion had been incidentally detected on cranial computed tomography in 2003 during treatment for bilateral subdural hematomas. Marked progression was observed in 2017, and magnetic resonance imaging in 2018 suggested a lower-grade glioma. Considering the patient’s advanced age, comorbidities, absence of documented neurological deterioration, and preferences, continued observation was chosen. In 2020, progressive headache, dizziness, dysarthria, left facial weakness, and left-sided limb weakness developed. Imaging revealed substantial enlargement of the right frontoparietal lesion with surrounding T2/FLAIR hyperintensity, ventricular compression, and midline shift. Subtotal resection was performed. Histopathological examination showed a cellular, diffusely infiltrating glioma with classic oligodendroglial morphology and appreciable mitotic activity. Immunohistochemistry demonstrated IDH1 R132H positivity, retained nuclear ATRX expression, and a Ki-67 labeling index of approximately 25%. Locus-specific fluorescence in situ hybridization detected deletion of the tested 1p36 and 19q13 loci. These integrated findings were highly suggestive of oligodendroglioma, with histological features that supported the original CNS WHO grade 3 designation; however, combined whole-arm loss of 1p and 19q was not independently confirmed. The patient received radiotherapy and procarbazine, lomustine, and vincristine chemotherapy. Tumor recurrence in 2022 was treated with repeat subtotal resection and focal re-irradiation. At the final follow-up, approximately 6 months after the second surgery, the patient and his family reported that he remained functionally independent in activities of daily living; formal neurological scale reassessment and follow-up imaging were unavailable. This case illustrates the approximately 19-year imaging evolution of an indeterminate intracranial lesion that preceded the diagnosis of an IDH1 R132H-mutant diffuse glioma with integrated features highly suggestive of oligodendroglioma. It highlights the importance of scheduled imaging surveillance and the need to distinguish locus-specific evidence of 1p/19q loss from definitive confirmation of combined whole-arm 1p/19q codeletion.