A 62-year-old woman is seen in the emergency department for progressive confusion, memory loss, and gait instability over a 6-month period with noticeable worsening over the last 2 months. She denies nausea, vomiting, lethargy, headache, fevers, chills, or night sweats. She smokes cigarettes (1 pack/day) and her family history is significant for breast cancer. On examination she is oriented to person, place, and time. Cranial nerves are intact and visual fields are full to confrontation. There is full strength in all extremities, sensation is intact, and reflexes are normal. She demonstrates instability with tandem walking and difficulty remembering 3 of 3 objects over a 5-minute period. Vital signs are normal and she is afebrile. Serum electrolytes, liver enzymes, glucose, complete blood cell count, and urinalysis results are normal. Computed tomography (CT) of the head demonstrates a mass in the third ventricle and significantly enlarged lateral ventricles with transependymal flow (Figure 1).