A 48-year-old woman undergoes MRI brain for chronic headaches. Imaging reveals a well-demarcated intra-axial mass in the frontal lobe. Which is the most common site of origin for glioblastoma multiforme in adults?

Explanation

## Most Common Site of Glioblastoma in Adults **Key Point:** The cerebral hemispheres, particularly the **frontal and temporal lobes**, are the most common sites of glioblastoma multiforme in adults, accounting for approximately 60–70% of cases. ### Anatomical Distribution of Glioblastoma | Location | Frequency in Adults | Frequency in Children | Notes | |----------|-------------------|----------------------|-------| | Cerebral hemispheres (frontal/temporal) | 60–70% | 20–30% | Most common in adults; often supratentorial | | Parietal lobe | 15–20% | Rare | Part of hemispheric distribution | | Occipital lobe | 10–15% | Rare | Part of hemispheric distribution | | Cerebellum | 5–10% | 40–50% | More common in children; infratentorial | | Brainstem | 2–5% | 10–15% | Rare in adults; more common in children | | Spinal cord | <1% | Rare | Extremely rare site for GBM | **High-Yield:** Glioblastoma is predominantly a **supratentorial** tumor in adults. The frontal lobe is the single most frequently affected region, followed by the temporal lobe. This contrasts sharply with pediatric gliomas, where infratentorial tumors (cerebellum, brainstem) are more common. ### Why the Frontal and Temporal Lobes? 1. **Vascular supply:** The middle cerebral artery (MCA) territory, which supplies the frontal and temporal lobes, is the largest vascular territory in the brain. Glioblastomas are highly vascular tumors and may preferentially arise in well-vascularized regions. 2. **White matter involvement:** Glioblastomas often arise at the gray-white matter junction and infiltrate white matter tracts. The frontal and temporal lobes have extensive white matter (corpus callosum, internal capsule). 3. **Cell of origin:** Glioblastomas likely arise from neural progenitor cells or dedifferentiated glial cells, which are abundant in the cerebral hemispheres. **Clinical Pearl:** Glioblastomas arising in the frontal lobe may present with personality changes, executive dysfunction, or motor deficits, while temporal lobe tumors may cause seizures, memory disturbance, or language dysfunction (if left-sided). ### Contrast with Pediatric Gliomas ```mermaid flowchart TD A[Glioma Location]:::outcome --> B{Age Group?}:::decision B -->|Adult| C[Supratentorial]:::outcome C --> D[Frontal/Temporal lobes<br/>60-70%]:::action B -->|Child| E[Infratentorial]:::outcome E --> F[Cerebellum/Brainstem<br/>50-60%]:::action ``` **Mnemonic for Glioma Sites — **SHIFT**: - **S**upratentorial (adults: frontal, temporal) - **H**emispheres (most common location) - **I**nfratentorial (children: cerebellum, brainstem) - **F**rontal > temporal (in adults) - **T**emporal (second most common in adults) ### Imaging Characteristics by Location - **Frontal lobe GBM:** Often large at presentation; may cross corpus callosum ("butterfly" glioma if bilateral); seizures common - **Temporal lobe GBM:** May present with seizures, memory loss, or language disturbance; may extend into insula - **Cerebellar GBM (rare in adults):** Presents with hydrocephalus, ataxia, increased ICP - **Brainstem GBM (rare in adults):** Presents with cranial nerve palsies, long tract signs **Warning:** Cerebellar and brainstem gliomas are *rare* in adults but *common* in children. Do not confuse the epidemiology of pediatric and adult CNS tumors — a frequent exam trap. [cite:Robbins 10e Ch 28] [cite:Harrison 21e Ch 449]