## Core Concept
The differentiation between parathyroid adenoma and hyperplasia is crucial in the management of primary hyperparathyroidism. Parathyroid adenoma is a benign tumor of a single parathyroid gland, whereas hyperplasia involves an increase in cell number in multiple glands. The distinction is important because the surgical approach differs.

## Why the Correct Answer is Right
The correct answer involves understanding the pathological and clinical features that distinguish adenoma from hyperplasia. A key feature is the **number of glands affected**. Parathyroid adenoma typically involves one gland, while hyperplasia involves multiple glands. Additionally, the **histological appearance** can provide clues, with adenomas usually showing a single large gland with a uniform cell population and hyperplasia showing multiple enlarged glands with a mix of cell types.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not provide a specific feature that differentiates adenoma from hyperplasia.
- **Option B:** Similarly, this option lacks specificity regarding the distinguishing features between adenoma and hyperplasia.
- **Option C:** This option might seem plausible but does not directly address a commonly used criterion for differentiation.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that **parathyroid adenoma accounts for about 85% of cases of primary hyperparathyroidism**, and it usually involves a single gland. In contrast, hyperplasia is less common and often associated with multiple gland involvement. Intraoperative parathyroid hormone (PTH) levels can help confirm the removal of the abnormal gland(s).

## Correct Answer Line
**Correct Answer: D.**