A 45-year-old man presents with progressive headaches, focal seizures, and cognitive decline over 6 months. MRI brain shows a heterogeneous intra-axial mass in the left frontal lobe with areas of necrosis and hemorrhage. Histopathology reveals glial cells with marked nuclear pleomorphism, high mitotic activity, and microvascular proliferation. What is the most common grade and type of glioma in adults?

Explanation

## Most Common Adult Glioma: Glioblastoma Multiforme **Key Point:** Glioblastoma multiforme (GBM, WHO Grade IV astrocytoma) is the most common primary malignant brain tumor in adults, accounting for approximately 45–50% of all primary CNS tumors and 80% of malignant gliomas. ### Epidemiology & Incidence - Peak incidence: 45–70 years of age - Incidence: 3–4 cases per 100,000 population per year - Represents the most aggressive glioma subtype ### Pathological Features (as in this case) 1. **Nuclear pleomorphism** — marked variation in cell size and shape 2. **High mitotic activity** — numerous mitotic figures 3. **Microvascular proliferation** — hallmark feature of Grade IV 4. **Necrosis** — often with pseudopalisading pattern 5. **Hemorrhage** — common finding on imaging and histology ### Clinical Presentation - Rapid onset of symptoms (weeks to months) - Headaches, seizures, focal neurological deficits - Cognitive or personality changes - Mass effect symptoms (increased ICP) ### Imaging Characteristics - Heterogeneous enhancement with gadolinium - Central necrosis with peripheral enhancement ("ring-enhancing" lesion) - Surrounding vasogenic edema - Often crosses midline (infiltrative) **High-Yield:** GBM is the **most common primary malignant brain tumor in adults**. The presence of microvascular proliferation and necrosis on histology is pathognomonic for Grade IV. **Clinical Pearl:** Despite aggressive multimodal therapy (surgery, radiation, chemotherapy with temozolomide), median overall survival remains only 12–15 months, making it one of the most lethal human cancers. ### Comparison with Other Gliomas | Feature | Grade II (Diffuse) | Grade III (Anaplastic) | Grade IV (GBM) | | --- | --- | --- | --- | | **Mitotic activity** | Low | Moderate–high | High | | **Necrosis** | Absent | Absent | Present (defining) | | **Microvascular proliferation** | Absent | Absent | Present (defining) | | **Median survival** | 5–10 years | 2–3 years | 12–15 months | | **Frequency in adults** | 10% | 10% | 50% | [cite:Robbins 10e Ch 28]