A 52-year-old woman undergoes imaging for progressive headaches and is found to have a brain tumor. Histopathology shows a tumor composed of cells with round nuclei, perinuclear halos, and a characteristic 'honeycomb' appearance. The tumor is WHO Grade II. In which location is this type of glioma most commonly found?

Explanation

## Most Common Site of Oligodendroglioma: Cerebral Hemispheres **Key Point:** Oligodendrogliomas are most commonly located in the **cerebral hemispheres, particularly in the white matter**, with a predilection for the frontal and parietal lobes. They account for 5–10% of all gliomas. ### Pathological Features (as described in the stem) - **Round nuclei** with uniform appearance - **Perinuclear halos** — characteristic clear space around the nucleus (artifact of fixation) - **Honeycomb or fried-egg appearance** — the classic histological hallmark - **WHO Grade II** — relatively indolent behavior ### Epidemiology & Location 1. **Most common site:** Cerebral hemispheres (frontal > parietal > temporal) 2. **White matter predilection** — arises from oligodendrocytes in white matter tracts 3. **Cortical involvement** — often extends to involve gray matter as well 4. **Bilateral involvement** — rare but possible ### Clinical Presentation - Seizures (40–60% of cases) — often the presenting symptom - Headaches - Focal neurological deficits (less common than with astrocytomas) - Slower progression than astrocytomas of equivalent grade ### Imaging Characteristics - Hypodense on CT, hypointense on T1-weighted MRI - Hyperintense on T2-weighted and FLAIR sequences - May show calcification (30–50% of cases) - Minimal surrounding edema - Enhancement is variable **High-Yield:** Oligodendrogliomas are **supratentorial tumors of the cerebral hemispheres**, not infratentorial. The "fried-egg" or "honeycomb" appearance is pathognomonic. Seizures are the most common presenting symptom. **Mnemonic:** **OLIGO** = **O**ver the **L**obes (cerebral hemispheres), **I**ndolent course, **G**ood prognosis (Grade II), **O**ligodendrocytes (cell of origin). ### Comparison of Glioma Sites | Glioma Type | Most Common Site | Key Feature | | --- | --- | --- | | **Oligodendroglioma** | Cerebral hemispheres (white matter) | Fried-egg appearance, seizures | | **Astrocytoma** | Cerebral hemispheres (white matter) | Infiltrative, variable grades | | **Ependymoma** | Ventricular system, 4th ventricle | Arises from ependymal lining | | **Medulloblastoma** | Cerebellum (4th ventricle) | Pediatric, highly malignant | | **Brainstem glioma** | Pons, midbrain | Pediatric, poor prognosis | **Clinical Pearl:** Oligodendrogliomas with 1p/19q co-deletion (now a defining molecular feature) have a significantly better prognosis and improved chemotherapy response compared to those without this deletion. [cite:Robbins 10e Ch 28]