**Core Concept**
Polycystic kidney disease (PKD) is a genetic disorder characterized by the growth of numerous cysts in the kidneys, leading to renal impairment. The disease is associated with cyst formation in other organs, particularly those with a similar embryological origin.

**Why the Correct Answer is Right**
Polycystic kidney disease is a systemic disorder that affects multiple organs, primarily those derived from the metanephric mesenchyme, such as the liver, pancreas, and spleen. The lung, however, is not a typical site for cyst formation in PKD, as it develops from a different embryological precursor, the endodermal foregut. The liver, pancreas, and spleen, on the other hand, are prone to cyst formation due to their shared embryological origin with the kidneys.

**Why Each Wrong Option is Incorrect**
**Option B:** The liver is a common site for cyst formation in PKD, with up to 25% of patients developing hepatic cysts. Liver cysts are thought to arise from the same embryological precursor as renal cysts.
**Option C:** Pancreatic cysts are also a known manifestation of PKD, occurring in approximately 5-10% of patients. These cysts are believed to arise from the same metanephric mesenchyme-derived cells as renal cysts.
**Option D:** Spleen cysts, although rare, have been reported in patients with PKD. The exact mechanism of cyst formation in the spleen is unclear, but it is thought to arise from the same embryological precursor as renal and hepatic cysts.

**Clinical Pearl / High-Yield Fact**
PKD is a systemic disorder that can affect multiple organs, and clinicians should maintain a high index of suspicion for extrarenal manifestations, particularly in patients with a family history of the disease.

**✓ Correct Answer: A. Lung**