**Core Concept**
Nephrocalcinosis is a condition characterized by the deposition of calcium salts in the renal tissue, often resulting from hypercalcemia, hyperphosphatemia, or increased urinary oxalate excretion. This condition can lead to renal damage and impairment.

**Why the Correct Answer is Right**
Nephrocalcinosis can be caused by a variety of factors, including primary hyperparathyroidism, vitamin D intoxication, and certain metabolic disorders such as hyperoxaluria. In these conditions, the increased levels of calcium or oxalate in the urine lead to the formation of calcium oxalate crystals in the renal tissue, causing nephrocalcinosis. The renal tubular cells attempt to reabsorb the calcium and oxalate, but this process can lead to cell damage and fibrosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Primary hyperparathyroidism is a known cause of nephrocalcinosis, so this option is incorrect as it is a condition associated with nephrocalcinosis.

**Option B:** Vitamin D intoxication can lead to hypercalcemia, which in turn can cause nephrocalcinosis. Therefore, this option is incorrect as it is a condition that can lead to nephrocalcinosis.

**Option C:** Hyperoxaluria is a metabolic disorder characterized by excessive excretion of oxalate in the urine, which can lead to the formation of calcium oxalate crystals in the renal tissue, causing nephrocalcinosis. So, this option is incorrect as it is a condition associated with nephrocalcinosis.

**Clinical Pearl / High-Yield Fact**
To remember the causes of nephrocalcinosis, recall the acronym "VIT D": Vitamin D (intoxication), Idiopathic (medullary sponge kidney), and Tubular (renal tubular acidosis) are all conditions that can lead to nephrocalcinosis.

**Correct Answer: D. Medullary sponge kidney is a condition characterized by cystic dilatation of the collecting ducts in the renal medulla, but it is not typically associated with nephrocalcinosis.