At least two of the "paradigmatic" clinical signs (malaise, high fever, costovertebral pain and tenderness, urinary syndrome) were present in all the cases; however, one patient had no flank pain, only about half had lower urinary symptoms and two patients were non-febrile at the time of diagnosis.Diagnostic criteria: the diagnosis of APN was based on involvement of the kidney parenchyma, as shown by CT or MR. "Simple" lesions take up the dye in a late phase and with a homogeneous pattern. At CT and MR scans, the lesions appear wedge-shaped, radiating from the papilla in the medulla to the cortical space, with or without swelling and with poor enhancement. "Abscessual" lesions are target-shaped: the central core does not show contrast uptake. The peripheral ring takes up the contrast media in a late phase.The lesion showing a "colliquative tendency" have an intermediate appearance: they are non-homogeneous and the target aspect is less pronounced.