Pyonephrosis in humans refers to infected urine in an obstructed collecting system. It can begin as pyelonephritis and then convert to pyonephrosis when outflow obstruction and hydronephrosis occurs (Figure 1 - at the top). The infection can result from an ascending lower urinary tract infection or from hematogenous spread of infection from a distant primary site.
The consequences of delayed diagnosis include urosepsis, renal abscess formation, and irreversible renal damage, which might require nephrectomy. Treating pyonephrosis with antimicrobial drugs without correction of the obstruction may still be potentially devastating for the patient.