Thalamic Tumors in Adults

Epidemiology and Diagnosis

The World Health Organization recommends evaluating all thalamic gliomas for H3 K27M mutations and loss of nuclear K27-trimethylated histone H3 (H3K27me3) by immunohistochemistry, as this mutation status fundamentally changes the diagnosis and prognosis 4
Diffuse midline glioma, H3 K27M-mutant, is a consideration in this anatomic location, carrying WHO grade IV designation, and arises in midline structures including the thalamus 1, 2, 3
The American Joint Committee on Cancer suggests that diffuse gliomas detected within bilateral thalami at diagnosis should prompt immediate H3 K27M mutant-specific IHC testing, as this mutation qualifies the tumor for the diagnosis of diffuse midline glioma, H3 K27M-mutant regardless of histologic grade 1, 2

The National Comprehensive Cancer Network notes that the vast majority of glioblastomas (90%) are IDH-wildtype, corresponding to de novo glioblastomas arising after age 55 years 1, 2
For patients over 55 years with histologically typical glioblastoma, immunohistochemical negativity for IDH1 R132H alone suffices for classification as IDH-wildtype glioblastoma, according to the College of American Pathologists 4
IDH-mutant glioblastomas predominate in younger adults and have comparably prolonged survival compared to IDH-wildtype tumors, as stated by the American Association for Cancer Research 1, 2

The International Society for Magnetic Resonance in Medicine suggests that neuroimaging characteristics, such as infiltrative lesions on T2-weighted MRI within the thalamus, can help narrow the differential diagnosis, with infiltrative lesions strongly suggesting diffuse glioma, while ring-enhancing lesions suggest glioblastoma 3