Polymorphous low-grade neuroepithelial tumour of the young (PLNTY)

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Status

Done

General

First described

In 2017
By Huse

May account for a proportion of oligodendroglioma-like tumours in the paediatric population

PLNTYs share significant histologic overlap with previous reports of “long‐term epilepsy associated tumors (LEATs)” and “pediatric oligodendroglioma”

Definition

Essential:

Diffuse growth pattern (at least regionally) AND
Oligodendroglioma-like components (although these may be minor) AND
Few (if any) mitotic figures AND
Regional CD34 expression by tumour cells and by ramified neural cells in associated cerebral cortex AND
IDH-wildtype status AND

Unequivocal expression of BRAF p.V600E on immunohistochemical assessment OR
Molecular diagnostic evidence of BRAF p.V600E mutations, FGFR2 or FGFR3 fusions, or potentially other МАРК pathway-driving genetic abnormalities

Desirable:

Conspicuous calcification (characteristic, although not constant)
Absence of 1 p/19q codeletion

CNS WHO grading

Grade 1

Numbers

Ranging in age from 4 to 57 years

Most occurring in the second and third decades of life (median age at diagnosis: 16 years)

Clinical presentation

Refractory epilepsy

Headache or dizziness

Origin

Tumours’ aberrant CD34 expression possibly reflecting an origin from developmentally dysregulated neural precursors

Pathology

Unencapsulated, soft to friable, grey-white masses that are indistinctly demarcated from normal brain

Demonstrates both infiltrative and compact growth patterns

Oligodendroglioma-like components with coarse calcification

Generally absent are

Foci of necrosis
Microvascular proliferation
Gemistocytic elements
Myxoid microcysts
Neurocytic rosettes
Rosenthal fibres

A collage of images of cells AI-generated content may be incorrect. — Polymorphous low-grade neuroepithelial tumour of the young. A, Oligodendroglioma-like features include small round nuclei, perinuclear haloes, and delicate branching capillaries. B, Mild nuclear pleomorphism and membrane irregularities are common. C, Astroglial elements here exhibit spindling and more conspicuous atypia without mitotic activity. D, Vascular mineralization was evident in this example. E, A diffuse growth pattern and conspicuous calcification are seen.

Genetic

Mutations affecting the MAPK pathway,

BRAF mutations
FGFR (particularly FGFR2 or FGFR3) fusions

Fusion transcript involving FGFR2 (including the kinase domain) joined with CTNNA3 (to include the entirety of its C‐terminal dimerization domain)
The resultant fusion is thought to lead to homodimerization and autophosphorylation of FGFR2 and downstream MAPK/PI3K/mTOR pathway activation

Location

Temporal lobe most often (80% of cases),

More so on the right than left

Subcortically

Radiology

Characteristic imaging appearances

Cortical/subcortical location in the temporal lobe
Calcification and cysts in the majority of cases

T2w

Hyperintense lesions
A granular appearing calcification pattern termed ‘salt and pepper sign’ on T2w sequences has been proposed as a potential manifestation of this type

MRI + C

Little or no contrast enhancement.

A close-up of a brain scan AI-generated content may be incorrect. — Polymorphous low grade neuroepithelial tumour of the young. FLAIR-hyperintense solid components, cystic changes, and the absence of mass effect are seen in this MRI.

Differential diagnosis

Features	PLNTY	Dysembryoplastic neuroepithelial tumour (DNET)
Calcification	More	Less
FLAIR	Less likely	Hyperintense rim
Size	Smaller	Bigger
Demarcation	Less	Better
Nodularity		Multinodular (soap bubble sign)

Prognosis

Amenable to control by excision

Tumour removal effected relief from seizures or reduced seizure frequency in most cases.

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