Diffuse leptomeningeal glioneuronal tumor (DLGNT) is a rare pediatric neoplasm categorized by the WHO in 2016. It is characterized by communicating hydrocephalus, slow tumor growth, CSF with absence of tumor cells, and MRI showing diffuse leptomeningeal enhancement and cystic changes. Here we present, to our knowledge, the first case in which direct cystic tumor infiltration of the optic apparatus was the initial manifestation.

A 3-year-old boy developed emesis, altered mental status, bilateral leg weakness, and decreased visual acuity to 20/125 OD and 20/160 OS. MRI showed hydrocephalus and diffuse leptomeningeal enhancement of the brain and spine. Lumbar puncture showed pleocytosis, elevated protein, positive enterovirus PCR, and opening pressure of 55 cm H2O.  VP shunt was placed for presumed enterovirus meningitis.  Symptoms of hydrocephalus resolved but vision did not improve.  Exam showed optic disc pallor bilaterally and no papilledema.  OCT demonstrated retinal nerve fiber layer thinning bilaterally. Visual decline progressed despite normalization of ICP.  Repeat MRI brain/orbits showed multiple new subpial cysts along the optic tracts and optic chiasm.  Filum biopsy showed rare inflammatory cell. Review of the pathology and radiological findings led to a consensus of DLGNT with cysts compressing and infiltrating optic chiasm and nerves.  The patient was started on the MEK inhibitor trametinib, with stabilization of MRI findings and vision, but unfortunately without visual improvement.

Pathologic confirmation of DLGNT can be difficult as safely obtained biopsy samples are typically small.  In this case, bilateral optic neuropathy developed due to infiltration of the optic nerves, chiasm and tracts, while papilledema was never seen.  MEK inhibitor therapy was initiated with Trametinib leading to stabilization in disease burden.  This diagnosis should be considered in pediatric patients with communicating hydrocephalus, diffuse leptomeningeal enhancement, and elevated CSF protein with otherwise normal profile including absence of tumor cells.