Non-specific histological variant of dysembryoplastic neuroepithelial tumor: a diagnostic challenge

Abstract

Abstract Objective The accurate diagnosis of the non-specific variant of dysembryoplastic neuroepithelial tumor (DNT) is very difficult because it is characterized by absence of the histological hallmark of the “specific glioneuronal element” in lesions. We herein present two cases of the non-specific form of DNT to analyze the clinical, radiological, and histological features of this unusual subtype of DNT. Methods A 16-year-old and a 23-year-old patient had been treated for pharmacoresistant epilepsy for several years before undergoing referral to the hospital for further examination and treatment. Magnetic resonance imaging (MRI) revealed that both patients had a small, well-demarcated cystic lesion within the cortex of the brain without obvious contrast enhancement or peritumoral edema. The lesions were totally resected and routinely examined using histological and immunohistochemical analysis. Results Both lesions exhibited similar histological appearances with cyst formation and mural nodule architecture. The glial nodules were mainly composed of oligodendrocyte-like components, and partly of piloid cells resembling pilocytic astrocytoma. The cortex adjacent to the lesion in both cases was found to have the histological features of focal cortical dysplasia (FCD) Type I. Immunohistochemically, the oligodendrocyte-like components were diffusely positive for Syn and Olig-2, but staining for CD34, p53, and IDH1 R132H was negative. The Ki-67 (MIB-1) labeling index was low, approximately 1%. There was no 1p/19q co-deletion in either lesion by fluorescence in situ hybridization (FISH) assay. Neither patient received postoperative adjuvant treatment, and both underwent regular follow-up for at least 24 months. No signs of recurrence or epileptic attacks were observed during the follow-up period. Conclusion The non-specific variant of DNT is a diagnostic challenge for pathologists in clinical practice, and differentiation from some low-grade gliomas needs to be considered. The careful inspection of radiologic and histopathologic findings, accompanied by analysis of patients’ clinical manifestations, may be helpful in making an accurate diagnosis.