## Distinguishing Oligodendroglioma from Astrocytoma ### Histopathological Features **Key Point:** The 'fried egg' appearance with perinuclear halos is the pathognomonic feature of oligodendroglioma, resulting from cell retraction artifact during fixation. | Feature | Oligodendroglioma | Astrocytoma | |---------|-------------------|-------------| | **Characteristic appearance** | Fried egg cells with perinuclear halos | Fibrillary background with Rosenthal fibers | | **Nuclear morphology** | Round, uniform nuclei | Irregular, hyperchromatic nuclei | | **Cytoplasm** | Clear, retracted from nucleus | Fibrillary, GFAP-positive | | **Necrosis pattern** | Chicken-wire capillary pattern | Pseudopalisading necrosis (high-grade) | | **Genetic marker** | 1p/19q co-deletion (favorable) | TP53 mutation, ATRX loss | ### Clinical Pearl **High-Yield:** Oligodendrogliomas with 1p/19q co-deletion have significantly better prognosis and chemosensitivity compared to astrocytomas. The 'fried egg' appearance is a light microscopy finding that should prompt immunohistochemistry (OLIG2+, SOX10+) and molecular testing for 1p/19q status. ### Immunohistochemical Correlation - **Oligodendroglioma:** OLIG2+, SOX10+, GFAP−/weak - **Astrocytoma:** GFAP+, OLIG2−, SOX10− **Mnemonic:** **FRIED EGG = OLIGO** — The classic fried egg appearance is virtually diagnostic of oligodendroglioma. [cite:Robbins 10e Ch 28] 
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