The axial FLAIR MRI of the brain shown above reveals a large, infiltrative lesion in the right temporo-parieto-occipital region. Which of the following is the most likely diagnosis?

Explanation

## Image Findings * **Large, ill-defined hyperintense lesion:** A significant area of increased signal intensity is noted in the right temporo-parieto-occipital region. * **Infiltrative margins:** The lesion lacks clear demarcation from the surrounding brain parenchyma, suggesting an infiltrative growth pattern. * **Mass effect:** There is effacement of the sulci adjacent to the lesion and mild compression of the right lateral ventricle, indicating significant mass effect. * **Extensive vasogenic edema:** The widespread hyperintensity on FLAIR, particularly around the lesion, is consistent with extensive vasogenic edema. * **Intra-axial location:** The lesion is clearly within the brain parenchyma, involving both cortical and subcortical structures. ## Diagnosis **Key Point:** The imaging features of a large, infiltrative, intra-axial lesion with extensive surrounding edema and significant mass effect are highly characteristic of a **Glioblastoma Multiforme (GBM)**. GBM is the most common and aggressive primary malignant brain tumor in adults. On FLAIR sequences, GBM typically appears as a heterogeneous, hyperintense mass with irregular, infiltrative margins and extensive surrounding vasogenic edema. While central necrosis and ring enhancement are classic features seen on post-contrast T1, the infiltrative nature and significant edema on FLAIR are strong indicators of a high-grade glioma. ## Differential Diagnosis | Feature | Glioblastoma Multiforme (GBM) | Meningioma | Cerebral Abscess | Multiple Sclerosis Plaque | | :------------------ | :---------------------------------------------------------- | :---------------------------------------------------------- | :---------------------------------------------------------- | :---------------------------------------------------------- | | **Location** | Intra-axial, often deep white matter, can involve cortex | Extra-axial (dural-based) | Intra-axial | Intra-axial, periventricular, juxtacortical, infratentorial | | **FLAIR Signal** | Heterogeneous hyperintense, extensive edema | Iso- to hypointense, variable edema | Hyperintense edema, central hypointense (pus) | Ovoid hyperintense, Dawson's fingers | | **Margins** | Ill-defined, infiltrative | Well-circumscribed, broad dural base | Well-defined capsule (rim enhancement on T1C) | Well-defined | | **Mass Effect** | Significant | Variable, often less than size suggests | Significant | Minimal to none | | **Enhancement (T1C)** | Irregular, ring-enhancing, central necrosis (not seen here) | Strong, homogeneous, dural tail sign | Ring-enhancing capsule, central non-enhancing | Variable, often no enhancement or faint patchy | ## Clinical Relevance **Clinical Pearl:** Patients with GBM often present with rapidly progressive neurological deficits, seizures, and symptoms of increased intracranial pressure (headache, nausea, vomiting). The prognosis is generally poor despite aggressive treatment. ## High-Yield for NEET PG **High-Yield:** Glioblastoma Multiforme is the most common primary malignant brain tumor in adults. It is characterized by rapid growth, extensive infiltration, and a poor prognosis. Histologically, it shows pseudopalisading necrosis and microvascular proliferation. **Key Point:** On imaging, GBMs are often described as having a 'butterfly' appearance when they cross the corpus callosum. ## Common Traps **Warning:** Differentiating GBM from a solitary brain metastasis or a large cerebral abscess solely on FLAIR can be challenging. Contrast-enhanced T1 sequences and Diffusion-Weighted Imaging (DWI) are crucial for definitive diagnosis, as metastases are often more circumscribed with prominent edema, and abscesses show restricted diffusion within the necrotic core. ## Reference [cite:Harrison's Principles of Internal Medicine, Ch 428; Robbins Basic Pathology, Ch 26]