This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney, Subject name: Medicine
Nephrocalcinosis is seen - 
Select and explain. 
A. Medullary sponge disease, B. Acute pyelonephritis, C. Acute glomerulonephritis, D. Chronic pyelonephritis
A: Medullary sponge disease
Answer: A: Medullary sponge disease 
Explanation: Medullary sponge kidney is one of several common causes of medullary nephrocalcinosis. Medullary nephrocalcinosis is defined as the deposition of calcium salts in the medulla of the kidney Nephrocalcinosis is a disorder that occurs when too much calcium is deposited in the kidneys. It commonly occurs in premature infants. Individuals may not have symptoms or may have symptoms related to the condition causing nephrocalcinosis. Later symptoms may be associated with chronic kidney failure. Ref Harrison20th edition pg 267