A 62-year-old man presents with progressive morning headaches and vomiting over 4 weeks, followed by a focal seizure. MRI with gadolinium shows a heterogeneous ring-enhancing mass with central necrosis and surrounding vasogenic edema. The structure marked **C** in the diagram demonstrates crossing of the corpus callosum in a characteristic butterfly pattern. Which of the following clinical features is MOST consistent with this imaging finding and best explains why this appearance is pathognomonic for the underlying diagnosis?
A. The butterfly pattern of corpus callosum crossing is highly characteristic of glioblastoma multiforme and helps differentiate it from brain metastases, which rarely cross the midline
B. The corpus callosum crossing indicates a low-grade glioma with indolent behavior and excellent long-term prognosis with radiation alone
C. The butterfly pattern represents hemorrhagic transformation of a venous infarction and suggests primary CNS lymphoma as the most likely diagnosis
D. The corpus callosum involvement indicates a secondary tumor from systemic malignancy and mandates staging CT of chest, abdomen, and pelvis
Explanation
Why option 1 is correct
The corpus callosum crossing in a butterfly pattern (marked C) is a pathognomonic imaging finding for glioblastoma multiforme. This characteristic appearance—where the tumor crosses the midline through the corpus callosum—is a key distinguishing feature that differentiates GBM from brain metastases, which typically occur at the gray-white junction and rarely cross the corpus callosum. The NCCN CNS Tumors Guidelines and Stupp Protocol emphasize this imaging distinction as critical for diagnosis. The rapid progression, ring enhancement with central necrosis, and vasogenic edema in a patient with acute neurological symptoms (seizure, morning headache with vomiting from raised ICP) over weeks to months are classic for GBM, the most aggressive primary brain tumor in adults with median survival of 15–18 months despite optimal therapy.
Why each distractor is wrong
Option 2: While corpus callosum involvement can occur in low-grade gliomas, the heterogeneous ring enhancement with central necrosis, rapid 4-week progression, and acute seizure presentation are hallmarks of high-grade GBM, not indolent low-grade disease. Low-grade gliomas typically present insidiously over months to years with homogeneous enhancement.
Option 3: Corpus callosum crossing is not a feature of primary CNS lymphoma or hemorrhagic venous infarction. Lymphoma typically shows homogeneous enhancement in immunocompetent patients and ring enhancement in HIV/immunocompromised states, but does not characteristically cross the corpus callosum in a butterfly pattern.
Option 4: While metastases can involve the corpus callosum, they typically do so as part of multifocal disease at gray-white junctions rather than as a solitary butterfly-pattern crossing. The singular, large, ring-enhancing mass with central necrosis and vasogenic edema is far more consistent with primary GBM than secondary metastatic disease.
High-YieldNEET PG
Corpus callosum crossing in a butterfly pattern on MRI is pathognomonic for glioblastoma and helps exclude metastases—a critical imaging-to-diagnosis link in neuro-oncology.
