A 65-year-old man is brought to the physician by his wife due to a one-month history of progressive, dull headaches that are most severe in the morning. His wife also notes that he has become increasingly apathetic and forgetful over the same time period. He has no significant past medical history and does not smoke cigarettes. Vital signs are within normal limits. On physical examination, he appears somnolent and has mild left-sided hemiparesis. An MRI of the brain with gadolinium contrast demonstrates a large, irregularly shaped, ring-enhancing mass in the right frontal lobe that extends across the corpus callosum into the left hemisphere, accompanied by significant surrounding vasogenic edema and midline shift.
Which of the following is the most likely diagnosis?
The correct answer is:
A) Glioblastoma
Glioblastoma is the most common and most aggressive primary malignant CNS tumor in adults. It typically presents in the 6th or 7th decade of life with signs of increased intracranial pressure such as morning headaches, nausea, or vomiting and focal neurological deficits. The classic radiographic finding is a "butterfly glioma," a large, ring-enhancing lesion with central necrosis that crosses the midline via the corpus callosum. The ring represents the highly cellular, vascularized periphery, while the center is necrotic.
Answer choice B: Meningioma, is incorrect. Meningiomas are typically slow-growing, benign, extra-axial tumors that arise from the arachnoid cells. On MRI, they appear as well-circumscribed, dural-based masses that enhance intensely and uniformly, often showing a dural tail. They do not typically cross the corpus callosum or show central ring-enhancement.
Answer choice C: Metastatic adenocarcinoma, is incorrect. Brain metastases are the most common cause of intracranial malignancy in adults. However, they typically present as multiple, well-circumscribed lesions located at the gray-white matter junction. While they can show ring enhancement, they rarely cross the corpus callosum in the butterfly distribution seen in this patient.
Answer choice D: Oligodendroglioma, is incorrect. These are slow-growing tumors typically found in the frontal lobes. They are characterized histologically by "fried-egg" cells and "chicken-wire" capillaries. Radiographically, they are often associated with calcification, which is not described here, and they lack the aggressive ring-enhancing and midline-crossing features of glioblastoma.
Answer choice E: Primary central nervous system (CNS) lymphoma, is incorrect. While primary CNS lymphoma (PCNSL) can cross the corpus callosum and show ring-enhancement, it is most commonly associated with severe immunosuppression (e.g., HIV/AIDS). In immunocompetent patients, it usually presents as a single, solidly enhancing lesion rather than an irregularly ring-enhancing mass with extensive central necrosis.
Key Learning Point
Glioblastoma is the most common primary malignant brain tumor in adults. It is characterized radiographically by an irregularly shaped, ring-enhancing mass that frequently crosses the corpus callosum (butterfly glioma). Histopathologically, it is defined by the presence of pseudopalisading necrosis and microvascular proliferation.
