INNV-58. Delayed diagnosis of diffuse leptomeningeal glioneuronal tumor in an adult

Abstract Diffuse leptomeningeal glioneuronal tumor (DLGNT) is a rare, predominantly pediatric tumor, with adult-onset cases being exceedingly uncommon. Symptoms are non-specific, often presenting with headaches or signs of elevated intracranial pressure. Due to the rarity of adult-onset cases and the insidious nature of symptoms, delays in diagnosis and treatment are common. Furthermore, limited data on DLGNT restricts understanding of optimal management strategies. We report a case of a 65-year-old male who presented with isolated headaches. Magnetic resonance imaging (MRI) revealed diffuse leptomeningeal contrast enhancement involving the brain and spinal cord. Lumbar puncture revealed elevated intracranial pressure with elevated protein and a lymphocytic pleocytosis. Cytology was negative for tumor cells. A biopsy was initially deferred, and the patient was treated empirically for neurosarcoidosis, without clinical improvement. Eventually a brain biopsy was performed, which confirmed the diagnosis of DLGNT harboring a BRAF V600E. The patient is managed with BRAF/MEK inhibition with dabrafenib and trametinib. These therapies target this molecular abnormality directly. With this case report, we hope to further the knowledge of adult-onset DLGNTs and to further emphasize the clinical importance of surgical biopsy in establishing a definitive diagnosis.