A 62-year-old right-handed man presents with 6 weeks of progressive morning headaches, nausea, a new focal-onset seizure, personality changes, and right-sided pyramidal weakness. Fundoscopy reveals bilateral papilloedema. MRI brain with gadolinium shows a heterogeneous mass centered in the splenium of the corpus callosum with a classic 'butterfly' configuration crossing the midline to involve both cerebral hemispheres. The structure marked **A** in the diagram—the ring-enhancing mass crossing the corpus callosum—demonstrates irregular thick rim enhancement around central necrosis with extensive surrounding vasogenic edema. MR spectroscopy shows elevated Cho:NAA ratio and lipid-lactate peaks. Based on this imaging signature, what is the most likely diagnosis?
A. Glioblastoma multiforme (WHO Grade 4 astrocytoma, IDH-wildtype)
B. Brain abscess with multiple loculations
C. Cerebral metastasis from a systemic primary malignancy
D. Primary CNS lymphoma in an immunocompetent host
Explanation
Why Glioblastoma multiforme (WHO Grade 4 astrocytoma, IDH-wildtype) is right
The imaging signature described—a ring-enhancing mass crossing the corpus callosum in a butterfly pattern with irregular thick rim enhancement, central necrosis, extensive vasogenic edema, and elevated Cho:NAA ratio with lipid-lactate peaks—is the classic presentation of glioblastoma multiforme. The butterfly configuration specifically indicates a lesion centered in the splenium of the corpus callosum extending across the midline to both hemispheres, which is pathognomonic for GBM. The irregular thick rim (not smooth), central necrosis, and MR spectroscopy findings (Cho:NAA > 2, lipid-lactate) confirm high-grade malignancy. GBM is the most common and most malignant primary brain tumor in adults (Harrison's 21e, Primary Tumors of the Nervous System).
Why each distractor is wrong
Primary CNS lymphoma in an immunocompetent host: CNS lymphoma typically presents with solid or homogeneous enhancement rather than ring enhancement with central necrosis. The irregular thick rim and butterfly pattern crossing the corpus callosum are not characteristic of lymphoma in immunocompetent patients.
Cerebral metastasis from a systemic primary malignancy: While metastases can present as ring-enhancing lesions, they typically occur at the gray-white matter junction and are usually multiple. A solitary lesion with butterfly configuration crossing the corpus callosum is far more characteristic of GBM than metastatic disease.
Brain abscess with multiple loculations: Abscesses typically show restricted diffusion on DWI and do not demonstrate the elevated Cho:NAA ratio or lipid-lactate peaks seen in this case. The clinical presentation (personality changes, seizure, progressive weakness) and imaging findings are inconsistent with infection.
High-YieldNEET PG
The butterfly pattern crossing the corpus callosum with irregular thick rim enhancement and central necrosis is pathognomonic for glioblastoma multiforme; remember MAGIC-D differential for ring-enhancing lesions, but GBM is favored by the butterfly configuration and spectroscopy findings.
Harrison's 21e, Primary Tumors of the Nervous System; NEJM 2005 STUPP Protocol
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