MICROSCOPIC DESCRIPTION: 1-2. Sections show cerebral cortex and white matter. There is a moderately cellular glial tumour. There is a proliferation of predominantly neoplastic oligodendroglial cells. They have enlarged round nuclei with perinuclear haloes. Intermixed neoplastic astrocytes are also present. These cells have more elongated and angulated nuclei. The background is fibrillary with cystic spaces and occasional calcification. The tumour extends into the cortex with secondary structuring including subpial accumulation and perineuronal satellitosis. A single mitosis is identified. No microvascular proliferation or necrosis is present.
IMMUNOHISTOCHEMISTRY: GFAP positive in tumour and reactive astrocytes; negative in tumour oligodendroglial cells NogoA positive in tumour oligodendroglial cells. IDH-1 R132H positive (mutated) ATRX positive (not mutated) MGMT positive (likely unmethylated) p53 negative p16 positive Topoisomerase labelling index: Approximately 2% The features are those of oligoastrocytoma (WHO Grade II).
DIAGNOSIS: oligoastrocytoma (NOS) (WHO Grade II)