USMLE Answer 21

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21. The correct answer is E. Seventy percent of adult brain tumors occur above the tentorium (70% of childhood tumors occur below the tentorium). Statistically, metastases > astrocytomas (including glioblastoma) > meningioma > pituitary tumor. Location at the junction of cortical gray and white matter is also typical for metastatic disease, as is the round shape.

Astrocytomas (choice A) typically arise in the white matter and have an irregular shape.

Ependymomas (choice B) are uncommon and arise from the ependymal lining of the ventricles.

Glioblastoma multiforme (choice C) is an aggressive form of astrocytoma that can cause a “butterfly lesion,” crossing between the cerebral hemispheres.

Meningiomas (choice D) can cause spherical lesions and are usually located on the surface of the brain.