A 47-year-old woman presents to the clinic for assessment of increasing headaches and visual changes. She has no prior history of headaches or migraines, and her only significant past medical history is pre-eclampsia during her first pregnancy. After delivery, her blood pressure returned to normal. On examination, her pupils are normal and reactive to light, the extraocular movements are normal, but there are visual field defects of the outer half in both eyes (bitemporal hemianopsia) The remaining neurologic examination is normal. Which of the following is the most likely diagnosis?