Polymorphous Low-Grade Neuroepithelial Tumor of the Young: A Case Report with Genomic Findings

Background: Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a recently recognized epileptogenic neuroepithelial tumor. Despite its distinctiveness, its polymorphous histology and the nature of its oligodendrocyte-like cells remain unclear. Case Description: A 30-year-old, right-handed man was diagnosed with intractable epilepsy since 22 years of age. Magnetic resonance imaging revealed T2 signal hyperintensity and corresponding T1 signal hypointensity within the subcortical white matter of the right middle temporal gyrus. Positron emission tomography scan demonstrated hypometabolism in the right anterior temporal region. Electroencephalography and stereo-electroencephalography monitoring localized seizures to the right temporal lobe, allowing the patient to undergo right temporal lobectomy. Histologic sections demonstrated cortical dysplasia, white matter heterotopia, and hippocampal reactive gliosis without neuronal loss. Interestingly, an approximately 6-mm subcortical neoplasm was identified in the temporal lobectomy. It was composed of well-differentiated oligodendroglial-like cells but exhibited mild-to-moderate nuclear variability and pleomorphism, and mild infiltration into the overlying cortex without perineuronal satellitosis. No mitotic activity, microvascular proliferation, or necrosis was identified, and Ki-67 labeling index was less than 1%. The tumor was diffusely CD34 positive with moderate glial fibrillary acidic protein and retained ATRX staining, and demonstrated the presence of the BRAF V600E mutation. The tumor was negative for reticulin condensation, synaptophysin, SMI31, neuronal nuclei immunostains, and both the IDH1 mutation and 1p19q codeletion. Overall histologic findings were most consistent with PLNTY. Conclusions: The correct diagnosis of PLNTY and its distinction from closely resembling low-grade neuroepithelial tumors is important. We hope our proposed diagnostic features will aid in its proper diagnosis and management.