The patient went on to have surgery.

Histology

Paraffin sections show a moderately hypercellular glial tumor with mixed morphology. Both oligodendroglial and astrocytic morphology is discernible and there is a prominent population of reactive astrocytes. Scattered mitotic figures are identified (3/20 HPF). A focus of microvascular proliferation with multi-layering of atypical cells around vessel lumens is demonstrated. No necrosis is identified.

IMMUNOHISTOCHEMISTRY:

• GFAP positive in astrocytic cells, negative in oligodendroglial cells.
• NogoA positive in oligodendroglial cells
• Nestin positive (low)
• IDH-1 R132H positive (mutated)
• ATRX negative (mutated)
• MGMT negative (likely methylated)
• p53 positive
• p16 CDKN2A positive
• Topoisomerase labeling index: Approximately 5%.

COMMENT: This glial tumor has mixed morphological features. Positive immunostaining for p53 and weak/negative staining for ATRX favor astrocytoma. However, many tumor cells show strong positive staining for NogoA indicating an oligodendroglial component. FISH for chromosome 1p/19q deletion is thus indicated. 

1p19q co-deletion:

• 1p/19q FISH 1p36 NO DELETION DETECTED
• 19q13.3 DELETION DETECTED 

FINAL DIAGNOSIS:

astrocytoma IDH-mutant (WHO CNS grade 3)

Discussion

This case is unusual and presumably represents a low-grade astrocytoma IDH-mutant which is in the process of becoming more aggressive.

Note, the presence of microvascular proliferation strictly speaking is sufficient to designate this tumor a WHO grade 4, however as the majority of this tumor does not demonstrate this feature, the absence of necrosis, preservation of CDKN2A and low-grade MRI appearances resulted in it being designated a grade 3 tumor by the pathologists.