A 64-year-old man presents with a 6-week history of progressive cognitive decline, memory loss, behavioural disinhibition, and gait imbalance. He has developed early-morning headaches (relieved by vomiting), focal seizures with secondary generalisation, and right hemiparesis. Examination reveals frontal lobe signs (grasp reflex, perseveration), bilateral papilledema, and bilateral upgoing plantars. Gadolinium-enhanced MRI brain is shown. The structure marked **A** in the diagram—the heterogeneously enhancing mass crossing the corpus callosum with bilateral frontal lobe extension—demonstrates the classic "butterfly glioma" configuration. Based on the imaging characteristics and clinical presentation, what is the most likely diagnosis?
A. Anaplastic astrocytoma (WHO Grade 3) with necrosis
B. Metastatic adenocarcinoma with leptomeningeal spread
C. Primary CNS lymphoma with corpus callosum involvement
D. Glioblastoma (CNS WHO Grade 4, IDH-wildtype)
Explanation
Why Glioblastoma (CNS WHO Grade 4, IDH-wildtype) is right
The structure marked A—a heterogeneously enhancing mass crossing the corpus callosum with bilateral frontal lobe extension forming a "butterfly" configuration—is pathognomonic for glioblastoma. The clinical presentation (progressive cognitive decline, frontal lobe signs, seizures, raised ICP) combined with imaging hallmarks (irregular thick peripheral enhancement, central necrosis, extensive vasogenic edema, elevated rCBV on perfusion imaging, and restricted diffusion in the solid rim) are diagnostic of WHO Grade 4 glioblastoma. The bilateral frontal involvement crossing the midline is the defining feature of butterfly glioma, which occurs in ~5% of glioblastomas and carries particular poor prognosis due to eloquent location preventing safe maximal resection (Wen PY et al. N Engl J Med 2015).
Why each distractor is wrong
Primary CNS lymphoma with corpus callosum involvement: CNS lymphoma typically shows homogeneous enhancement without necrosis and uniform diffusion restriction. The heterogeneous enhancement with central necrosis and elevated rCBV are atypical for lymphoma, which does not usually demonstrate the degree of vasogenic edema seen here.
Anaplastic astrocytoma (WHO Grade 3) with necrosis: While Grade 3 tumors can show enhancement and necrosis, the degree of heterogeneous enhancement, extensive central necrosis, markedly elevated rCBV (>3.0), and the classic butterfly distribution crossing the corpus callosum are more consistent with Grade 4 glioblastoma. Grade 3 tumors typically have lower perfusion metrics.
Metastatic adenocarcinoma with leptomeningeal spread: Metastases typically present as multiple discrete lesions with well-defined margins and less extensive infiltrative edema. The single large infiltrative mass with butterfly configuration crossing the corpus callosum is characteristic of primary glioblastoma, not metastatic disease.
High-YieldNEET PG
Butterfly glioma = heterogeneously enhancing mass crossing the corpus callosum with bilateral frontal lobe extension; classic for glioblastoma; poor prognosis due to eloquent location limiting surgical resection.
Wen PY et al. Glioma Groups Based on 1p/19q, IDH, and TERT Promoter Mutations in Tumors. N Engl J Med 2015;372(26):2499-2508.
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