Diffuse hemispheric gliomas, H3 G34 mutant are rare and high grade infiltrating tumors typically presenting in adolescents and young adults.
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Terminology
Diffuse hemispheric gliomas H3 G34 mutant have been recently included in the 5th Edition (2021) of the WHO brain tumor classification 1 among the "pediatric-type diffuse high-grade gliomas" (WHO grade 4).
Epidemiology
Diffuse hemispheric gliomas H3 G34 mutant generally occur in adolescents and young adults 2, although cases in older patients have been reported 3.
Pathology
Location
Diffuse hemispheric gliomas H3 G34 mutant are usually supratentorial tumors, often multifocal, arising mainly in temporal and parietal lobes 2. Similarly to glioblastomas in adults, they may cross the midline structures and have leptomeningeal spread.
Microscopic appearance
These tumors typically demonstrate astrocytic cells with glioblastoma-like features such as high cellularity, brisk mitotic activity and infiltrative growing. Microvascular proliferation and necrosis may be present. They also often show an embryonal-like appearance with smaller cells and hyperchromatic nuclei 2.
Immunochemistry
They show a high Ki-67 proliferation index 2.
Radiographic features
Diffuse hemispheric gliomas H3 G34 mutant are similar to other high-grade gliomas.
MRI
Hyperintense multifocal lesions in T2 and FLAIR sequences infiltrating the white matter and exert mass effect on surrounding cerebral structures. After administration of contrast media, they usually show foci or subtle areas of enhancement 3. In addition, necrotic and/or hemorrhagic areas, calcifications and cystic changes may be seen 4.
Treatment and prognosis
Diffuse hemispheric gliomas H3 G34 mutant carries a poor prognosis with a median survival of 18-22 months 2,3. Treatment is surgical, with adjuvant radiotherapy and chemotherapy.
Differential diagnosis
Differential diagnosis includes the other pediatric-type diffuse high-grade gliomas:
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