What is the difference between pyelonephritis and hydronephrosis?

Pyelonephritis is an infection of the kidney, typically caused by bacteria, leading to inflammation and potentially affecting kidney function. In contrast, hydronephrosis is a condition characterized by the swelling of a kidney due to the build-up of urine, often resulting from an obstruction in the urinary tract. While pyelonephritis can lead to hydronephrosis, the two conditions are distinct, with different causes, symptoms, and treatment approaches.