[Pyelonephritis].

Acute pyelonephritis (APN) is a frequent pathological condition. Its etiology is prevalently due to E. coli and risk factors include sexual activity, genetic predisposition, old age and urinary instrumentation. No correlation between APN and vesicoureteral reflux has been established in adults. The diagnosis of APN is usually clinical, but computed tomography (CT) and magnetic resonance imaging (MRI) allow a more precise definition and can document evidence of abscesses. Severe cases should be treated with a fluoroquinolone or an extended-spectrum cephalosporin. Treatment should last 10-14 days. The long-term evolution of APN is prevalently favorable in adults, even though formation of cortical scars and development of macroalbuminuria and renal failure have been described. The formation of renal abscesses is underestimated and must be evaluated by CT or MRI. Abscesses need to be drained only when they are large, and medical treatment is successful in the majority of cases.