**Core Concept**
Hyperparathyroidism is a disorder characterized by an overproduction of parathyroid hormone (PTH), leading to an imbalance in calcium and phosphate levels in the body. This hormonal imbalance can cause a range of radiological features, including changes in bone density, soft tissue calcification, and renal abnormalities.

**Why the Correct Answer is Right**
The correct answer is related to the radiological feature of brown tumors, which are characteristic of primary hyperparathyroidism. Brown tumors are a type of bone lesion that forms in response to the increased levels of PTH, which leads to an increase in osteoclast activity and bone resorption. These lesions are typically seen in the jaw, pelvis, and long bones and appear as well-defined, expansile masses on radiographs. The presence of brown tumors is an important diagnostic feature of primary hyperparathyroidism.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is not a specific radiological feature of hyperparathyroidism. While osteoporosis is a common complication of hyperparathyroidism, it is not a specific radiological feature.
* **Option B:** This option is incorrect because it is not a characteristic radiological feature of hyperparathyroidism. While renal calculi are a common complication of hyperparathyroidism, they are not a specific radiological feature.
* **Option C:** This option is incorrect because it is not a specific radiological feature of hyperparathyroidism. While bone cysts can be seen in a variety of conditions, they are not a characteristic feature of hyperparathyroidism.

**Clinical Pearl / High-Yield Fact**
Brown tumors are a classic radiological feature of primary hyperparathyroidism and should be considered when evaluating patients with hyperparathyroidism and characteristic bone lesions.

**Correct Answer: C. Brown tumors**