Calvarial erosion secondary to epithelioid glioblastoma: A molecularly characterized case report

Background: Epithelioid glioblastoma (eGBM) is a rare, aggressive IDH-wildtype glioblastoma of children and young adults. It is typically B-Raf proto-oncogene, serine/threonine kinase (BRAF) valine-to-glutamic acid substitution at amino acid position 600 (V600E)/ cyclin-dependent kinase inhibitor 2A (CDKN2A)/ cyclin-dependent kinase inhibitor 2B (CDKN2B) -altered. Calvarial erosion with extracranial extension is exceptionally rare and may mimic primary calvarial or extra-axial tumors. Case Description: A 16-year-old girl presented with a 2-week history of headache and a new-onset generalized tonic-clonic seizure. Neuroimaging revealed a superficially located left temporal intra-axial lesion with heterogeneous enhancement, extensive vasogenic edema, focal dural enhancement, and a through-and-through temporal squamous bone defect suggesting transdural extension. The patient underwent a left temporal craniotomy and tumor resection. The temporal squama was completely eroded, and the tumor breached the dura and extended beyond the inner table, confirming extracranial spread. Gross-total resection, including involved bone and dura with reconstruction, was achieved without postoperative complications or neurological deficit. Histopathology showed eGBM, central nervous system World Health Organization grade 4, with rhabdoid features, necrosis, subpial condensation, and meningeal involvement. Molecular profiling demonstrated BRAF V600E, telomerase reverse transcriptase (TERT) promoter −146C>T, CDKN2A/2B homozygous deletion, and methylthioadenosine phosphorylase (MTAP) loss, with isocitrate dehydrogenase 1 (NADP+) (IDH1)/ isocitrate dehydrogenase 2 (NADP+) (IDH2) and H3F3A wildtype, low tumor mutational burden, and microsatellite stability. Despite standard chemoradiotherapy, the patient passed away 6 months after diagnosis. Conclusion: eGBM may present with calvarial erosion and surgically confirmed extracranial extension in pediatric patients. Recognition of skull defects and dural enhancement should prompt planning for en bloc resection of invaded bone and dura with reconstruction and early comprehensive molecular testing to identify actionable targets such as BRAF V600E.