Polymorphous low-grade neuroepithelial tumor of the young: a case report.

Objective: To investigate the clinical, imaging, pathological, and molecular characteristics of polymorphous low-grade neuroepithelial tumor of the young (PLNTY) and provide references for clinical diagnosis and treatment. Method: We retrospectively analyzed the clinical data of one pathologically confirmed PLNTY patient, including medical history, clinical symptoms, imaging findings, pathological morphological features, immunohistochemical results and molecular testing data, and reviewed relevant literature. Result: A 30-year-old male patient presented with a 6-year history of drug-resistant epilepsy as the primary manifestation, which progressed from focal facial myoclonus to mixed seizure phenotypes. Cranial magnetic resonance imaging (MRI) demonstrated an ovoid area of abnormal signal intensity in the left temporal pole, exhibiting isointensity on T1-weighted imaging (T1WI), hypointensity on T2-weighted imaging (T2WI) and fluid-attenuated inversion recovery (FLAIR) sequences, and no enhancement following contrast administration; the initial radiological impression was a suspected cavernous hemangioma. Twenty-four-hour video electroencephalography (vEEG) identified abnormal epileptiform discharges originating from the left anterior temporal lobe. Subsequent to left temporal lobe lesionectomy, pathological examination confirmed the diagnosis of polymorphous low-grade neuroepithelial tumor of the young (PLNTY), CNS WHO Grade 1. Microscopically, the lesion was characterized by thin-walled vascular clusters, focal vascular wall hyalinization, calcification, and adjacent reactive glial proliferation. Immunohistochemical (IHC) staining revealed diffuse CD34 positivity, glial fibrillary acidic protein (GFAP) (+), oligodendrocyte transcription factor 2 (Olig-2) (+), and a Ki-67 proliferation index of 1%, indicating low proliferative activity. Molecular testing confirmed BRAF mutation positivity, weak immunoreactivity for BRAF V600E (detected via VE1 antibody), and absence of malignant-associated mutations. Postoperatively, the patient achieved complete seizure control and remained seizure-free with uneventful recovery at the latest follow-up. Conclusion: PLNTY is typically characterized by long-standing drug-resistant epilepsy and has a predilection for the temporal lobe, with potential atypical imaging manifestations (e.g., hypointensity on T2WI as observed in this case). Definitive diagnosis requires the integration of pathological morphology, immunohistochemistry, and molecular testing. PLNTY harboring the BRAF V600E mutation exhibits indolent biological behavior; gross total resection serves as the core therapeutic modality, conferring a favorable prognosis. Molecular subtyping can guide individualized follow-up strategies, and clinicians should be vigilant against misdiagnosis of cases with atypical imaging features.