**Core Concept**
Hypopituitarism in adults is a condition characterized by the diminished secretion of one or more anterior pituitary hormones. This condition can result from various causes, including infarction of the pituitary gland.

**Why the Correct Answer is Right**
Simmonds' disease, also known as primary hypopituitarism, is indeed caused by the infarction or destruction of the pituitary gland, leading to a deficiency in one or more pituitary hormones. This can occur due to various reasons such as pituitary apoplexy, head trauma, or vascular events. The pituitary gland is highly vascular, and its infarction can lead to a sudden loss of function, resulting in hypopituitarism.

**Why Each Wrong Option is Incorrect**
**Option B:** Hilton's disease is not a recognized term in the context of hypopituitarism or pituitary disorders. This option is likely a distractor and should be eliminated.
**Option C:** Wilson disease is a genetic disorder that leads to copper accumulation in the body, particularly affecting the liver and brain, but it is not associated with hypopituitarism or pituitary infarction.
**Option D:** Addison disease is a condition characterized by the deficiency of adrenal cortical hormones, which is a result of adrenal gland failure, not pituitary gland infarction.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that Simmonds' disease can be caused by various factors, including pituitary apoplexy, which is an acute hemorrhagic infarction of the pituitary gland. This condition requires prompt medical attention to prevent further complications.

**Correct Answer Line**
✓ Correct Answer: A. Simmonds’ diseases