A 49-year-old woman has had a severe headache for 2 days. On physical examination, she is afebrile and normotensive. Funduscopic examination shows papilledema on the right. One day later, she has the right pupillary dilation and impaired ocular movement. She then becomes obtunded. Which of the following lesions best explains these findings?

The papilledema and the herniation are a consequence of brain swelling, typically the vasogenic form of edema from blood-brain barrier disruption adjacent to the neoplasm. A large aggressive neoplasm, such as glioblastoma, may produce a mass effect via enlargement from rapid growth, hemorrhage, and surrounding edema. The mass effect with herniation of the medial temporal lobe results in a third cranial nerve palsy as the nerve is compressed. A chronic subdural hemorrhage accumulates slowly enough that herniation may not occur. An abscess may cause a mass effect with some associated brain swelling, but this patient is afebrile. There is no pressure effect with hydrocephalus ex vacuo, which is a consequence of cerebral atrophy. An infarct is not likely to produce pronounced associated brain swelling, and a mass effect in the occipital lobe is unlikely to affect the third nerve. Rupture of a berry aneurysm produces subarachnoid hemorrhage at the base of the brain, which is less likely to cause a mass effect.