A 45-year-old man presented to the emergency department because of persistent steady flank pain for 18 h. He denied having any systemic illness or trauma. On arrival, his vital signs were normal. Physical examination showed knocking tenderness over his left flank. His laboratory results disclosed leucocytosis (white cells 10 700/l), mildly raised serum creatinine (1.1 mg/dl) and aspartate aminotransferase (78 U/l). The urinary analysis showed absence of pyuria or haematuria. Ultrasonography of the kidneys showed no hydronephrosis, but a hypoechoic area over the lower portion of the left kidney. Contrast-enhanced computed tomography confirmed the diagnosis of acute renal infarction (fig 1A, arrow). Angiography of the left renal artery showed several segmental thrombi (arrows) in the left main renal artery (fig 1B). Intra-artery thrombolytic treatment with urokinase was carried out. Follow-up angiography showed patency of the affected artery. On follow-up at 2 months his serum creatinine was normal, but a renal scan showed 52% loss of estimated renal perfusion flow in the affected kidney. The diagnosis of renal infarction is often delayed. Nevertheless, neither clinical characteristics nor laboratory tests are sufficient to make the diagnosis. Early-stage renal infarction may present as a hypoechogenic area in ultrasonography.1 In patients with persistent flank pain but lack of evidence of calculus, a contrast-enhanced computed tomography is warranted to elucidate the possibility of renal infarction.

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Figure 1 (A) Contrast-enhanced computed tomography of abdomen confirmed the diagnosis of acute renal infarction (arrow). (B) Angiography of the left renal artery showed several segmental thrombi (arrows) in the left main renal artery.