Leptomeningeal dissemination in children is typical of high-grade, and occasionally low-grade,
neoplasms. Rare cases of widely disseminated oligodendroglia-like leptomeningeal
tumors, sometimes with associated spinal cord lesions, have been described that respond to treatment and follow an indolent course. Whether these lesions represent an established
tumor category or are a unique entity remains to be established. We present 9 pediatric cases of such diffuse leptomeningeal
neuroepithelial tumors (DLNT), 8 with assessment of 2 common genetic alterations seen in
oligodendrogliomas, 1p and 19q chromosomal deletions and
isocitrate dehydrogenase-1 (IDH1) R132H mutations. Four patients were male and 5 female, with a mean age at presentation of 4 years (range, 2 to 7 y). All presented with signs of increased intracranial pressure and diffuse contrast enhancement of the leptomeninges by magnetic resonance imaging. Three had a cervical or upper thoracic
spinal cord tumor, and another had a small cerebellar lesion. Leptomeningeal biopsies showed a thickened and fibrotic arachnoid infiltrated by monotonous cells with round nuclei and prominent perinuclear clearing. All cases were strongly immunoreactive for
S100 protein, and most showed faint granular
synaptophysin reactivity. Six of 8 cases showed deletions of chromosome arm 1p by fluorescence in situ hybridization, 2 of which also had loss of 19q. None of the lesions reacted with IDH1-R132H
antibodies. Although the clinicopathologic features show overlap of these DLNT lesions with
oligodendroglioma and extraventricular
neurocytoma, they do not exactly match either one, suggesting that DLNTs are a distinct
tumor entity.