Discrepancy between radiological and histological findings in ganglioglioma of the optic chasm: Case report

BACKGROUND: Gangliogliomas involving the optic nerve or chiasm are extremely rare tumors, which can be confused radiologically with other neoplasms. α-[N-methyl-(11)C]-methylaminoisobutyric acid ((11)C-MeAIB) is a new artificial amino acid positron emission tomography (PET) tracer, which is metabolically more stable in vivo and may be more specific for tumors than (11)C-methionine. However, the utility of (11)C-MeAIB PET in the diagnosis of brain tumors has not yet been reported. CASE DESCRIPTION: A 26-year-old man presented with visual field defects and headache, and magnetic resonance imaging demonstrated a suprasellar mass involving the optic chiasm. A biopsy and partial tumor resection were performed via an interhemispheric approach. We diagnosed the tumor as ganglioglioma (WHO grade I) involving the optic chiasm. Although this lesion was histologically benign, (11)C-MeAIB PET, 2-deoxy-2-[(18)F] fluoro-D-glucose ((18)F-FDG) PET and proton magnetic resonance spectroscopy indicated malignant features. CONCLUSION: The discrepancy between radiological and histological findings implies that this new amino acid tracer PET may have a limitation in the diagnosis of gangliogliomas. Although further study is necessary, gangliogliomas should be included in the differential diagnosis of suprasellar tumors, even if PET findings show malignant features.