Pyelonephritis is most commonly defined as which of the following?

Pyelonephritis is characterized by inflammation of the kidney tissue and the renal pelvis, which is the area where urine collects before it moves to the ureter. This condition typically results from a bacterial infection that ascends from the lower urinary tract, leading to infection and resultant inflammation in both the renal parenchyma and the renal pelvis.

The correct definition of pyelonephritis involves this dual inflammation, which is essential for understanding its clinical manifestations and implications. It can manifest as flank pain, fever, and urinary symptoms, which arise due to the involvement of both kidney structures and the collecting systems. Therefore, referring to pyelonephritis as a combination of renal and pelvic inflammation accurately encompasses the breadth of the condition and explains the pathophysiological changes that occur during the infection.