A 52-year-old man presents with progressive headaches, focal seizures, and cognitive decline over 6 months. MRI brain shows a heterogeneous mass in the left frontal lobe with central necrosis and peripheral edema. Histopathology reveals high cellularity with marked nuclear pleomorphism, brisk mitotic activity, and microvascular proliferation. What is the most common grade of glioma in adults?

Explanation

## Most Common Grade of Glioma in Adults **Key Point:** Glioblastoma multiforme (Grade IV) is the most common primary malignant brain tumor in adults, accounting for approximately 45–50% of all gliomas and 15% of all primary CNS tumors. ### Epidemiology and Incidence | Grade | Tumor Type | Incidence in Adults | Median Survival | |-------|-----------|-------------------|------------------| | IV | Glioblastoma (GBM) | 45–50% of gliomas | 12–15 months | | III | Anaplastic astrocytoma/oligodendroglioma | 10–15% of gliomas | 2–3 years | | II | Diffuse astrocytoma/oligodendroglioma | 20–25% of gliomas | 5–10 years | | I | Pilocytic astrocytoma | Rare in adults; common in children | Excellent | **High-Yield:** Glioblastoma is the most aggressive and most common malignant glioma. It arises either *de novo* (primary GBM, ~90% of cases) or through malignant transformation of lower-grade gliomas (secondary GBM, ~10% of cases). ### Pathological Features of Grade IV Glioblastoma 1. **Cellular characteristics:** - Marked nuclear pleomorphism - High mitotic rate (>10 mitoses per 10 HPF) - Necrosis (often with pseudopalisading pattern) - Microvascular proliferation 2. **Imaging hallmarks:** - Heterogeneous enhancement with gadolinium - Central necrosis ("ring enhancement") - Surrounding vasogenic edema - Infiltrative margins **Clinical Pearl:** The presence of necrosis and microvascular proliferation on histology is diagnostic of Grade IV disease and distinguishes it from Grade III anaplastic gliomas, which lack these features. ### WHO 2021 Classification Update The WHO 2021 classification now incorporates **IDH mutation status** and **1p/19q codeletion** as key prognostic markers: - **IDH-wildtype GBM** (most common, ~90% of primary GBM): worse prognosis - **IDH-mutant GBM** (~10%, usually secondary): better prognosis than IDH-wildtype **Mnemonic for GBM Features:** **NMPEC** - **N**ecrosis - **M**icrovascular proliferation - **P**leomorphism (nuclear) - **E**dema (vasogenic, perilesional) - **C**ellularity (high) ### Clinical Presentation Glioblastoma typically presents with: - Progressive headaches (50–70%) - Focal neurological deficits (seizures, weakness, speech disturbance) - Cognitive/behavioral changes - Symptoms often rapid (weeks to months) **Warning:** Grade I pilocytic astrocytomas are common in *children* (especially in the posterior fossa and optic nerve), not adults. In adults, they are rare and typically found in the optic pathway or brainstem. [cite:Robbins 10e Ch 28] [cite:WHO Classification of Tumours of the Central Nervous System 2021]