BACKGROUND: Often the reduced contrast enhancement on CT renal imaging is radiologically interpreted as acute pyelonephritis (PNA), but it is the task of the clinician to assess a possible differential diagnosis such as a renal infarct and look for a cause. METHODS: In our experience (2010-2013), we hospitalized 51 patients with radiological imaging consistent with acute pyelonephritis in native kidneys. However, three of these cases result, after a second look, to be ischemic lesions, only sometimes complicated by over-infections (Tabella 1). FIRST CASE: a woman hospitalized for fever and flank pain with blood culture positive for Klebsiella Pneumoniae. Antibiotic therapy allowed a clinical-laboratory improvement, but after 45 days persisted a focal wedge to the CT scan. The labs showed a anemia due to a sickle cell disease (SLC). The overview was finally interpreted as a renal infarct secondary to a sickle cell anemia, initially complicated by over-infection. SECOND CASE: a men hospitalized for a acute flank pain. The CT scan showed a left renal infarct and a partial renal artery thrombosis, resulting in abuse of cannabinoids and LAC positivity.Third case: a woman hospitalized for flank pain and slight movement of inflammatory markers. CT showed a cuneiform area in the right kidney not vascularized, that did not resolved after prolonged antibiotic therapy. The labs evidence a heterozygous mutation of prothrombin and MTHFR causing the renal infarction. CONCLUSIONS: 6% of radiographic imaging consistent with acute pyelonephritis concealed an underlying infarct, due to a unknown state of thrombophilia. The presence of hypovascular imaging to the TC scan, therefore, requires a differential diagnosis between PNA and infarct, especially in the case of atypical development.