Polymorphous Low-Grade Neuroepithelial Tumor of the Young (PLNTY): A Rare Entity

This report describes a case of polymorphous low-grade neuroepithelial tumor of the young (PLNTY) with an unusual immunohistochemical profile that was diagnosed with next-generation sequencing.

An 11-year-old female presented with a seizure and was found to have a 3.3 cm right temporal calcified mass with mild heterogeneous enhancement most consistent with a low-grade glioma. The mass was biopsied. Sections showed a moderately cellular neoplasm composed of oval to elongate cells with clumped chromatin, scant cytoplasm, irregular nuclear contours, and rare mitotic figures within a fibrillary background with delicate branching capillaries and microcalcifications. The neoplastic cells were diffusely positive for synaptophysin and negative for NeuN. Additionally, the cells had a patchy positivity for CD34 and p16, rare positivity for SOX10 and GFAP, strong positivity for p53 in 20% of cells, absence of BRAF V600E and IDH1 R132H mutant proteins, retained nuclear expression of ATRX, and a Ki67 index of 3%. Next-generation sequencing revealed an FGFR2::SHTN1 fusion.

This case illustrates the increasing centrality of molecular testing in the diagnosis of central nervous system (CNS) tumors and the impact of recent advances in CNS tumor classification on the care of pediatric patients.