H3K27M-Mutant Diffuse Leptomeningeal Glioneuronal Tumor Presenting as Communicating Hydrocephalus: Case Report and Literature Review.

INTRODUCTION: Diffuse leptomeningeal glioneuronal tumor (DLGNT) with H3K27M mutation is a rare and potentially fatal condition, with only a few cases reported in the literature. We present an unusual case of DLGNT presenting with communicating hydrocephalus secondary to leptomeningeal spread, initially misdiagnosed as idiopathic intracranial hypertension (IIH), with coexisting BRAF-KIAA1549 fusion and H3K27M mutation. CASE PRESENTATION: An 11-year-old boy presented with progressive, painless bilateral vision loss. Initial neuroimaging findings were misinterpreted as IIH, and a programmable ventriculoperitoneal (VP) shunt was placed. However, the underlying communicating hydrocephalus was secondary to leptomeningeal spread of DLGNT. Three months later, the patient developed lower limb weakness, and repeat imaging revealed diffuse leptomeningeal disease with spinal involvement. Histopathology and molecular testing confirmed DLGNT harboring both H3K27M mutation and BRAF-KIAA1549 fusion. Despite planned multimodal therapy, the patient experienced rapid neurological deterioration and died four months after diagnosis. CONCLUSION: This case demonstrates that DLGNT can present with communicating hydrocephalus secondary to leptomeningeal spread, which may be misdiagnosed as IIH. Early comprehensive neuroaxis imaging, prompt molecular characterization, and close surveillance are essential in pediatric patients with communicating hydrocephalus of unclear etiology.