This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oncology, Subject name: Medicine
A 57-year-old man is referred for assessment of his low serum sodium of 125 mEq/L. On examination, he has pitting edema and elevated neck veins. His urine sodium is 10 mEq/L and urine osmolality 350 mOsm/kg.For the above patient with hyponatremia, select the most likely diagnosis. 
Select and explain. 
A. congestive heart failure (CHF), B. extrarenal sodium and fluid losses, C. SIADH, D. polydipsia
A: congestive heart failure (CHF)
Answer: A: congestive heart failure (CHF) 
Explanation: Hyponatremia associated with nephrotic syndrome, cirrhosis, or CHF is characterized by edema. It is believed that the hyponatremia is caused by a decrease in "effective" circulating volume secondary to decreased cardiac output or sequestration of fluid.