Polymorphous low grade neuroepithelial tumor of the young

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is an epileptogenic tumor of children and young adults. They are often considered part of the heterogeneous group of tumors known as long-term epilepsy-associated tumors (LEATs).

Terminology

First described in 2016 ¹, polymorphous low-grade neuroepithelial tumor of the young has been included in the new family of "pediatric-type" low-grade diffuse gliomas in the 5^th Edition (2021) WHO brain tumor classification ² (WHO grade 1 tumor).

Epidemiology

Polymorphous low-grade neuroepithelial tumor of the young mainly occurs in children and young adults ³.

Clinical presentation

Most of the patients present with drug-refractory epilepsy ^3,6.

Pathology

Location

Polymorphous low-grade neuroepithelial tumor of the young commonly arises from the cortex and in the temporal lobes, although other locations have been reported (such as frontal, parietal, and occipital lobes) ^3,4,6.

Microscopic appearance, immunochemistry and genetics

Polymorphous low-grade neuroepithelial tumor of the young is typically characterized by oligodendroglioma-like cellular elements, calcifications, and a strong CD34 immunopositivity. Moreover, it frequently shows the mutation of BRAF V600E gene and fibroblast growth factor receptors 2 and 3, all of them involved in the regulation of the MAPK oncogenic pathway ^3-5.

Radiographic features

Polymorphous low-grade neuroepithelial tumors of the young display a solid or partially cystic appearance with unclear margins. They typically involve the cortex and subjacent white matter of the temporal lobe but usually do not produce a significant mass effect ^3-6.

CT

Polymorphous low-grade neuroepithelial tumor of the young may appear as a hypo- or hyperdense mass. They are frequently calcified, often with central coarse calcification ^3-6.

MRI

• T1: iso- or hypointense

• T2/FLAIR

  • heterogeneous hyperintensity with the "salt and pepper" sign (likely due to calcifications) ⁶

  • cystic components are variable in number and size ⁶

• T2*/SWI

  • patterns of calcification are variable

  • small punctate calficications are common particularly in younger patients ⁶

  • larger coarse central "blooming" calcifications are though to be typical ⁶

• DWI/ADC: no restricted diffusion

• T1 C+ (Gd)

  • slight or no enhancement ^3-6.

  • presence of enhancement has been raised as potentially heralding increased risk of recurrence ⁷, although this is not reproduced in all series ⁶

Treatment and prognosis

Surgery is curative and therefore the prognosis is good ^3-5.

Differential diagnosis

Differential diagnosis generally includes other epileptogenic entities ³.

• ganglioglioma and gangliocytoma

  • similar appearance and location

  • also fairly frequently has calcifications

• papillary glioneuronal tumor

  • can be indistinguishable on imaging

  • rare

• pleomorphic xanthoastrocytoma (PXA)

  • similar appearance and location

  • often very vivid contrast enhancement

  • may have a dural tail sign

• dysembryoplastic neuroepithelial tumor (DNET)

  • soap-bubble appearance and bright rim sign

  • enhancement less common and less intense if present

• oligodendroglioma

  • usually occurs in middle aged adults

  • less commonly arises in the temporal lobes

  • calcifications are common, tend to be "ribbon-like" or peripherally distributed

• focal cortical dysplasia

  • characterized by the thickening of the cortex,

  • blurring of white matter-grey matter junction and the transmantle sign

  • no enhancement

• calcifying pseudoneoplasm of the neuraxis (CAPNON)

  • almost entirely calcified

  • usually extra-axial (but can be intra-axial)