**Core Concept**
Hypopituitarism refers to the deficiency of one or more anterior pituitary hormones due to various causes. The pituitary gland regulates hormone secretion from other endocrine glands, and its dysfunction can have significant effects on overall health.

**Why the Correct Answer is Right**
The causes of hypopituitarism can be broadly classified into three categories: congenital, infiltrative, and ischemic. Congenital causes include genetic mutations that affect pituitary gland development, such as septo-optic dysplasia. Infiltrative causes include benign and malignant tumors, as well as autoimmune disorders like lymphocytic hypophysitis. Ischemic causes can result from pituitary apoplexy, which is often due to a hemorrhagic infarction of a pituitary adenoma.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a known cause of hypopituitarism. However, without more information, it is difficult to assess its relevance.
**Option B:** This option is incorrect as it does not accurately describe a cause of hypopituitarism. While radiation therapy can cause hypopituitarism, it is not a direct cause.
**Option C:** This option is incorrect as it does not accurately describe a cause of hypopituitarism. While certain medications can affect pituitary function, they are not a primary cause of hypopituitarism.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that hypopituitarism can be caused by a wide range of factors, and a thorough diagnostic workup is necessary to identify the underlying cause.

**Correct Answer:** D.