## **Core Concept**
Polycystic kidney disease (PKD) is a genetic disorder characterized by the growth of numerous cysts in the kidneys. The two main types are Autosomal Dominant Polycystic Kidney Disease (ADPKD) and Autosomal Recessive Polycystic Kidney Disease (ARPKD). Both types can lead to kidney enlargement and impair kidney function over time.

## **Why the Correct Answer is Right**
The correct answer, **D. Liver**, is associated with the fact that while polycystic kidney disease primarily affects the kidneys, not all organs are equally or commonly involved in a cystic manner. However, it's known that ADPKD is associated with cysts in other organs, notably the liver (liver cysts are common), but the question seems to seek an organ not typically involved in "all cases."

## **Why Each Wrong Option is Incorrect**
- **Option A: Kidneys** - This is incorrect because polycystic kidney disease by definition involves cysts in the kidneys in virtually all cases.
- **Option B: Pancreas** - This is incorrect because pancreatic cysts can occur in patients with ADPKD, although less commonly than liver cysts.
- **Option C: Brain** - This is incorrect because while not as commonly discussed, cerebral aneurysms (not exactly "cysts") are a concern in ADPKD, suggesting some vascular involvement in the brain.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that ADPKD is associated with an increased risk of liver cysts, which are often found incidentally and are usually asymptomatic. The presence of multiple liver cysts is more common in women and increases with age.

## **Correct Answer: D. Liver.**