Mesial temporal lobe rosette-forming glioneuronal tumor : an unusual location for a rare tumor

Excerpt

A left-handed 55-year-old female with an unremarkable medical history was admitted to the hospital with episodes of headache, paroxysmal bad smell, speech and behavior problems, sense of fainting and episodes of seizures lasting for a few minutes. Clinically, complex partial seizure was considered. Magnetic resonance imaging (MR) of the brain was performed and revealed a 27 × 22 × 21 mm mass in the right hippocampus. The mass was iso-hypointense and heterogeneously hyperintense to cortical gray matter on T1 and T2-weighted MR images, respectively. There was no enhancement in the tumor on gadolinium-enhanced images. The choline (Cho) peak was increased and the N-acetyl aspartate (NAA) peak was reduced on single voxel MR spectroscopy. The Cho/NAA ratio was 1.13 (Fig. 1). A low-grade glioma was suggested. Surgery was performed with total tumor resection. Microscopic evaluation of the lesion revealed a biphasic tumor showing glial and neurocytic components. The neurocytic part was composed of neurocytic tumor cells, forming neurocytic rosettes and pseudorosettes which lie in a mucinous and microcystic matrix in some areas of the tumor. The dominant neoplastic glial component of the tumor was composed of oval and elongated nuclei with moderately dense chromatin. Immunohistochemical analysis confirmed the presence of neurocytic and perivascular pseudorosettes by immunoreactivity for synaptophysin either at the centers of rosettes or in cytoplasms of neurocytic tumor cells. Glial component showed immunopositivity for GFAP and immunonegative for IDH1 and P53. Ki-67 was 1% (Fig. 2). Due to the typical histomorphological and immunohistochemical findings, the lesion was diagnosed as a rosette-forming glioneuronal tumor (RGNT) of the hippocampal region. …