Diagnosis was based on the presence of at least one of the 3 main symptoms (fever, costovertebral angle tenderness or pain, recent or present UTI) and at least one sign of systemic infection (high WBC or CRP). The presence of leukocytes or nitrites was an ancillary criterion supporting the presence of UTI.On the basis of their radiological appearance, the lesions were dichotomized in " simple" versus abscessed (at least one abscessed lesion) and in single versus multiple. The diagnosis of pyelonephritis required demonstration of involvement of the kidney parenchyma.