This case demonstrates contiguous brainstem and left globus pallidus / internal capsule lesion with multiple ring-enhancing areas. The appearances and location raise the possibilities of rhomboencephalitis or a high-grade glioma, with the later favored based on the clinical setting. Metastatic disease was felt unlikely given the distribution.

MICROSCOPIC DESCRIPTION: 1-3. Sections show fragments of a moderately hypercellular astrocytic glioma. Tumor cells show moderate nuclear and cellular pleomorphism. Scattered mitotic figures are identified. There is prominent microvascular proliferation with multilayering of atypical cells around the vessel lumen. Focal areas of palisaded tumor necrosis are also identified.

Immunohistochemistry results show tumor cells stain:

• GFAP Positive
• Nestin Positive (high)
• NogoA Positive
• IDH1 R132H Negative (non-mutated)
• ATRX Positive (non-mutated)
• p53 Equivocal
• p16 CDKN2A Negative

Topoisomerase labeling index: 20%.

DIAGNOSIS: Brain tissue, biopsy: High-grade glioma with necrosis

The differential diagnoses include IDH1 wild-type Glioblastoma (WHO Grade IV) and anaplastic oligodendroglioma (WHO Grade III). Molecular testing for IDH1/2 mutation, 1p19q codeletion and H3K27M mutation will be performed.

SUPPLEMENTARY REPORT:

• IDH 1 and 2 and H3F3A sequencing:
  • IDH-1 no variant detected (IDH-1 wild type)
  • IDH-2 no variant detected (IDH-2 wild type)
• H3F3A sequencing
  • Codon 27: no variant detected
  • Codon 34: no variant detected
• FISH for chromosome 1p/19q deletion.
  • Chromosome 1
    • Mean copies 1p per cell: 1.72
    • Mean copies 1q per cell: 1.65
    • 1p/1q ratio: 1.04
    • Interpretation: No 1p loss detected by FISH
  • Chromosome 19
    • Mean copies 19q per cell: 1.73
    • Mean copies 19p per cell: 1.78
    • 19q/19p ratio: 0.97
    • Interpretation: No 19q loss detected by FISH
  • SUMMARY: No 1p/19q co-deletion detected

FINAL DIAGNOSIS: "Brain stem tumor": Glioblastoma IDH wild type (WHO Grade IV).