October 2018 Case
A 22 year old male presented with confusion and delusional ideation and was found to have a 1.5cm non-enhancing intraventricular/midline septum pellucidum mass with obstructive hydrocephalus.
On immunohistochemistry (IHC), the tumor demonstrated appreciable Ki-67 and lacked IDH-1 expression. FISH was consistent with a lack of 1p19q co-deletion. BRAF mutations were absent via next-generation sequencing (NGS).
Dysembryoplastic neuroepithelial tumor of the septum pellucidum
Dysembryoplastic neuroepithelial tumor (DNET) is a well-defined entity that classically occurs in the cerebral cortex of children and young adults.
Histologically, DNETs present as a unique combination of features to include intracortical location, multinodular architecture, heterogeneous cellular composition and frequent association with cortical dysplasia.1
The anatomic spectrum of DNETs has expanded to include the cerebral cortex, pons, thalamus, basal ganglia, cerebellum, third ventricle, caudate nucleus and septum pellucidum.
Although DNETs are molecularly distinct entities lacking 1p19q deletions found in oligodendrogliomas and frequently harboring BRAF V600E mutations2, when occurring in the septum pellucidum, diagnosis and distinction from a close mimic, oligodendroglioma, can be difficult due to shared histological features.
1. Baisden BL1, Brat DJ, Melhem ER, Rosenblum MK, King AP, Burger PC. Dysembryoplastic neuroepithelial tumor-like neoplasm of the septum pellucidum: a lesion often misdiagnosed as glioma: report of 10 cases. Am J Surg Pathol. 2001 Apr;25(4):494-9.
2. Ibrahim Qaddoumi, Wilda Orisme, Ji Wen. Genetic alterations in uncommon lowgrade neuroepithleial tumors: BRAF, FGFR1, and MYB mutations occur at high frequency and align with morphology. Acta Neuropathol. 2016 Jun; 131(6); 833-845.
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