Diffuse leptomeningeal glioneuronal tumor (DLGNT) is defined in the WHO 2016 update as a new entity of neuronal and mixed neuronal-glial tumors. It consists of neoplastic glial and neuronal components with diffuse leptomeningeal involvement, usually in pediatric patients. Survival outcomes vary, but 40% of patients experience rapid progression. Due to the rarity of this entity there are no clear guidelines for management. Approaches described in the literature include craniospinal radiation therapy alone or in combination with different chemotherapeutic regimens.

Case Report: 13 year-old African American girl with past medical history of hemoglobin SS disease and alpha thalassemia who presented with encephalopathy and headache. MRI showed T2/FLAIR enhancing lesions with diffuse leptomeningeal enhancement involving the basal cisterns and spinal cord. Infectious and inflammatory etiologies were pursued but unrevealing. Encephalopathy and headache resolved the next day. The patient was discharged and lost to follow up. Five months later she presented with similar symptoms. Repeat MRI showed mild progression of disease, which prompted meningeal biopsy.

Biopsy showed monomorphous cells with round nuclei and clear cytoplasm positive for GFAP, S-100 and synaptophysin, consistent with DLGNT. IDH was non-mutated and there was insufficient sample to identify MGMT methylation and 1p19q deletions.

She was treated with temozolomide. Repeat MRI at three and six months showed no progression of disease. She has remained neurologically intact for eight months.

Given the patient's slow progression of disease and African American ethnicity, the leading diagnosis was initially sarcoidosis. A meningeal biopsy was fundamental in order to avoid misdiagnosis and erroneous management. Although rare, DLGNT should be in the differential for leptomeningeal disease especially in slowly progressive pediatric cases. Temozolomide is a reasonable chemotherapy option, but more studies are necessary to define a standard approach in these patients.