Final answer:
The 20-year-old man with palpable flank mass and hematuria showing bilateral enlarged kidneys with cysts on ultrasound likely has polycystic kidney disease, which can be associated with brain anomalies such as intracranial aneurysms.
Step-by-step explanation:
The case described suggests that the 20-year-old man may have polycystic kidney disease (PKD), which is a genetic disorder characterized by the growth of numerous cysts in the kidneys. Symptoms can include hematuria, flank pain, hypertension, and potentially renal failure. When PKD is diagnosed, it's important to also consider associated extrarenal manifestations, one of which includes brain anomalies. One such associated brain condition is an intracranial aneurysm. Although not mentioned explicitly in the provided information, it is known that intracranial aneurysms can be more common in patients with PKD.