Pyonephrosis

Pyonephrosis is a severe form of obstructive uropathy characterized by the accumulation of pus within the renal collecting system, leading to destruction of renal parenchyma. It typically results from an infected hydronephrosis, where an obstruction prevents the drainage of infected urine from the kidney. This condition is a medical emergency requiring prompt diagnosis and intervention to prevent sepsis and preserve renal function.

This code is used when documentation clearly indicates the presence of pus within the kidney, often in conjunction with hydronephrosis and signs of infection. It applies to cases where imaging studies (e.g., ultrasound, CT scan) confirm the presence of purulent material in the renal pelvis and calyces. Documentation should specify "pyonephrosis" or describe the clinical and radiological findings consistent with this diagnosis.

• Differentiate from simple hydronephrosis (N13.30-N13.39) or hydroureter (N13.2) unless infection and pus are explicitly documented.
• Always code the underlying cause of the obstruction (e.g., calculus, stricture, tumor) if known, as a secondary diagnosis.
• Consider additional codes for sepsis (A41.-) if documented, and for any associated urinary tract infection (N39.0).