Pituitary Disorders USMLE Step 1 Practice Question
A 54-year-old woman undergoes pituitary surgery for a non-functioning macroadenoma. On postoperative day 1, she develops polyuria (800 mL/hour) and severe thirst. Vital signs show HR 102/min, BP 138/88 mmHg, RR 16/min. Laboratory studies reveal serum sodium 165 mEq/L, osmolality 320 mOsm/kg, and urine osmolality 100 mOsm/kg. Urine specific gravity is 1.002. She denies recent diarrhea. Which pathophysiologic mechanism best explains these findings?
Answer choices
- ASyndrome of inappropriate antidiuretic hormone secretion
- BHypovolemic shock from surgical bleeding
- CPrimary polydipsia from anesthesia effects
- DTransient central diabetes insipidus from ADH depletionCorrect answer
- EHyperaldosteronism from surgical stress
- FCerebral salt wasting with natriuresis from posterior fossa manipulation
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.