Diffuse astrocytoma MYB or MYBL1 altered is a newly recognized IDH wildtype pediatric-type diffuse low-grade glioma included in the 5th Edition (2021) WHO brain tumor classification 1. It has a generally favorable prognosis and is often associated with seizures 4.
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Epidemiology
Diffuse astrocytoma MYB or MYBL1 altered occurs in children and young adults (median age 5 years; range 0-26 years) 3.
Pathology
Diffuse astrocytoma MYB or MYBL1 altered is closely related, from a molecular point of view, to angiocentric gliomas that also share MYB alterations but lack their histological features 8.
They are also closely related to isomorphic diffuse gliomas, not yet recognized as a distinct entity under the current (2021) WHO brain tumor classification, that also share MYBL1 alterations but tend to occur in adults and have a distinct methylation profile 8.
Location
hemispheres
diencephalon
brainstem 3
Microscopic appearance
Non-specific and low-grade histopathologic features with rare or absent mitotic activity 1,3.
Genetics
As these tumors are histologically non-specific it is essential to identify MYB/MYBL1 mutations for the diagnosis.
MYB or MYBL1 alternations 1,3,4
H3 wildtype
IDH wildtype
Radiographic features
The hemispheric cortical tumors appear as lobulated and infiltrative masses, while poorly defined and diffuse in the diencephalon and brainstem 3.
MRI
T1: iso- or hypointense
T2/FLAIR: heterogeneous hyperintensity
DWI/ADC: no restricted diffusion
T1 C+ (Gd): no enhancement 3
Treatment and prognosis
Although further studies are needed, the prognosis of these tumors is generally good 3.
Differential diagnosis
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pediatric-type diffuse low-grade gliomas:
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pediatric-type diffuse high-grade gliomas:
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