Infant-type hemispheric gliomas, also known as infant high-grade gliomas, are high-grade brain tumors occurring in children.
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Terminology
Infant-type hemispheric gliomas belong to the family of "pediatric high-grade diffuse gliomas" of the 2021 WHO Classification of Tumors of the Central Nervous System 1. They have been recognized as a novel tumor type distinct from other pediatric high-grade gliomas, harboring molecular mutations involving the receptor tyrosine kinases NTRK, ROS1, ALK, and MET.
Epidemiology
Infant-type hemispheric gliomas typically arise in the first year of life (range: 0–12 months) 2.
Pathology
Subtypes
infant-type hemispheric glioma, NTRK-altered
infant-type hemispheric glioma, ROS1-altered
infant-type hemispheric glioma, ALK-altered
infant-type hemispheric glioma, MET-altered
Location
They are usually supratentorial 2,3.
Microscopic appearance
Infant-type hemispheric gliomas show astrocytic cells arranged in fascicles or sheets with mild to moderate pleomorphism. Moreover, like the other high-grade gliomas, they often display palisading necrosis, mitotic activity, and endothelial proliferation 2,3.
Immunophenotype and molecular alterations
GFAP: positive
ALK: sometimes positive in the infant-type hemispheric glioma ALK-altered
diagnosis of these tumors generally requires detection of the fusion genes of tyrosine kinase NTRK1, NTRK2, NTRK3, ROS1, ALK, MET or, alternatively, a characteristic methylation profile 1-3
Radiographic features
An infant-type hemispheric glioma usually appears as a huge supratentorial mass with vasogenic edema, exerting a significant mass effect on the surrounding intracranial structures. Cases of leptomeningeal dissemination have been reported 4.
MRI
show a heterogeneous signal on T1W and T2W sequences, often with necrosis and hemorrhage
enhancement is present and is heterogeneous 2,3
Treatment and prognosis
More studies are needed to evaluate the survival rate and impact of targeted therapies. Infant-type hemispheric glioma ALK-altered subtype seems to have a better 5-year survival rate than the ROS1- and NTRK-altered subtypes 2.