**Core Concept**
Adult polycystic kidney disease (APKD) is a genetic disorder characterized by the growth of numerous cysts filled with fluid in the kidneys, leading to kidney enlargement and potential kidney failure. The condition is associated with various extrarenal manifestations, including cardiovascular complications.

**Why the Correct Answer is Right**
The vascular complications of APKD are primarily due to the presence of aneurysms in the intracranial and abdominal aorta. The aneurysms are thought to be caused by the systemic effects of cystatin C, a protein produced by the cysts that affects vascular smooth muscle cells, leading to weakening of the arterial walls. The risk of aneurysm formation is significantly increased in patients with APKD, especially in those with a family history of the condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Atherosclerosis is a common vascular complication in the general population but is not specifically associated with APKD.
**Option B:** Hypertension is a common finding in APKD, but it is not a vascular complication in itself.
**Option C:** Thrombosis is not a direct vascular complication of APKD, although patients may be at increased risk of thrombotic events due to underlying cardiovascular disease.

**Clinical Pearl / High-Yield Fact**
Patients with APKD are at increased risk of developing intracranial aneurysms, which can lead to subarachnoid hemorrhage. Regular screening for vascular complications is essential in the management of APKD.

**Correct Answer: C. Intracranial and abdominal aortic aneurysms.**