Pyonephrosis is a medical condition that occurs when the kidney becomes infected and filled with pus. Synonyms for pyonephrosis may vary from more technical terms such as renal abscess and suppurative nephritis to general phrases such as kidney abscess or pus-filled kidney. Other synonyms may include renal sepsis, infected hydronephrosis, and pyogenic nephrosis. Additionally, terms such as empyema of the kidney and renal pyogenic infection may also describe this condition. Regardless of the term that is used to describe pyonephrosis, the condition can be serious and requires prompt and effective medical treatment to prevent further complications from occurring.