**Core Concept**
Pituitary adenomas are benign epithelial tumors arising from the pituitary gland, accounting for a significant proportion of intracranial tumors. These tumors can be functioning or non-functioning, depending on the production of excess hormones.

**Why the Correct Answer is Right**
Pituitary adenomas are relatively common, accounting for approximately 10-15% of all intracranial tumors. They can vary in size and location, but most are confined within the sella turcica. Prolactinomas are the most common type of functioning pituitary adenoma, accounting for about 40% of all functioning adenomas. Reticulin staining is a useful tool in differentiating pituitary adenomas from other types of tumors, as it highlights the characteristic reticular pattern of the adenoma cells.

**Why Each Wrong Option is Incorrect**
**Option A:** While pituitary adenomas do account for a significant proportion of brain tumors, the exact percentage can vary depending on the population studied. However, stating that they account for 10% of brain tumors is an oversimplification.
**Option B:** Pituitary adenomas typically arise within the sella turcica and do not erode the sella. Instead, they can expand and compress surrounding structures.
**Option C:** Prolactinomas are actually the most common type of functioning pituitary adenoma, not the least common.
**Option D:** While reticulin staining can be useful in differentiating pituitary adenomas, it is not the only method and is not exclusive to these tumors.

**Clinical Pearl / High-Yield Fact**
Pituitary adenomas are often asymptomatic until they cause mass effect or hormonal imbalance. A high index of suspicion is required for early diagnosis and treatment.

**Correct Answer: A. Accounts for 10% of brain tumors**