Oligodendroglioma (IDH-mt, 1p19q codeleted)

In the left posterior part of the superior frontal gyrus, extending medially to involve the anterosuperior part of the paracentral lobule, there is a region of hypoattenuation with the involvement of the overlying cortex and positive mass effect. There is associated low attenuation in the white matter extending into the precentral gyrus (edema/tumor spread). On postcontrast imaging, no abnormal enhancement is demonstrated. The remainder of the brain is unremarkable in appearance. Ventricles are within normal limits in size. No focal osseous lesion. Small subcutaneous nodule is demonstrated beneath the left parietal scalp, most likely representing a sebaceous cyst/epidermal cyst. 

Correlating to the low density on CT brain, centered at the posterior-most aspect of the left superior frontal gyrus, is a moderate-sized area of FLAIR intensity involving and expanding cortex and with local mass-effect. The abnormal signal extends posteriorly to the precentral gyrus mainly medial to the hand knob. They are small foci of FLAIR hypointensity in and no definite enhancement. Only small area of mild diffusion restriction is present. MRS demonstrates mild reversal of the choline-creatine peak and mildly reduced NAA. No increased CBV. No susceptibility. Equivocal overlying bony remodeling. Paranasal sinus mucosal disease. 

MICROSCOPIC DESCRIPTION:

Sections show a moderately cellular tumor composed of cells containing round to oval, hyperchromatic, vesicular nuclei with inconspicuous nucleoli and prominent perinuclear clearing. Tumor cells are arranged in diffuse sheets intersected by thin-walled "chicken-wire" capillaries. Secondary structuring with perineuronal satellitosis and subpial condensation are noted. Focal microcystic change is seen. No calcifications are seen. Occasional mitotic figures are identified (up to 2/10hpf). No necrosis or microvascular proliferation is seen. 

IMMUNOHISTOCHEMISTRY: GFAP Positive Nogo A Positive Nestin Positive (intermediate) IDH-1 R132H Positive (mutated) ATRX Positive (non-mutated) MGMT Negative (likely methylated) p53 Negative p16 Positive Topoisomerase labeling index: 10%. 

FISH for chromosome 1p/19q deletion. 

1p36 DELETION DETECTED 19q13.3 DELETION DETECTED 

• Number of cells scored 200 
• Number of sites scored 10
• 1p36/1q25 ratio 0.69 
• 19q13.3/19p13 ratio 0.58 

REFERENCE CRITERIA: 

• 1p36/1q25 ratio <0.8 Deletion detected 
• 19q13.3/19p23 ratio <0.8 Deletion detected 

FINAL DIAGNOSIS: Oligodendroglioma, IDH-mutated, 1p/19q co-deleted (WHO Grade II)