Q. A 31-year-old female is two days postpartum and had a complicated delivery. She experienced uterine atony and subsequently lost approximately 3 pints of blood. The patient became symptomatic and was resuscitated with whole blood and normal saline secondary to prolonged hypotension. She delivered a healthy 8 lb 6 oz (3.8 kg) baby boy with APGARs of 7 at 1 minute, and 9 at 5 minutes. The infant has not been feeding well. Lactation consultants evaluated her earlier today and determined the mother is not producing milk. You are called to evaluate her. She has no other significant past medical history and only takes prenatal vitamins. The patient denies any history of alcohol, tobacco, or illicit drug use. She reports having hot flashes since the delivery, and otherwise has no complaints. On physical examination, she is afebrile, her blood pressure is 125/80 mm Hg, heart rate 80/min, respiratory rate 18/min, and her oxygen saturation is 99 percent on room air. Her cranial nerves are grossly intact, and she is alert and oriented. Her neck is supple, with no masses or lymphadenopathy. Cardiopulmonary assessment is within normal limits. You examine her breast and find no evidence of lactation, no skin lesions or evidence of mastitis. Her remaining physical examination is unremarkable. You order blood work, which reveals a hemoglobin of 7.8 g/dL, a serum sodium of 128 mEq/L, glucose of 65 mg/dL, and low levels of growth hormone, prolactin, and follicle-stimulating hormone. Levels of luteinizing hormone, adrenocorticotropic hormone, and thyroid-stimulating hormone, are normal. You are concerned about a pituitary mass and order a brain MRI (see image), which shows no mass and identifies an empty sella. Based on the information you have at this point in time, which of the following is the most likely diagnosis?