Acute focal bacterial nephritis and prolonged fever.

Acute focal bacterial nephritis (AFBN) is characterised by a complicated upper urinary tract infection ranging from acute pyelonephritis to renal abscess. Timely diagnosis of AFBN is important because antibiotic therapy of longer duration is required. A 10-year-old boy presented with fever for 5 days and bilateral flank pain. He was oriented and cooperative but appeared ill. Physical examination did not reveal any oedema or costovertebral angle tenderness. Acute phase reactants such as erythrocyte sedimentation rate and C-reactive protein were raised, serum creatinine was 1.25 mg/dL (0.31-0.88) and leucocyte esterase was positive in the urine. Ultrasonographic examination demonstrated bilaterally enlarged kidneys with increased echogenicity. Because of the high creatinine level, abdominal magnetic resonance imaging (MRI) was performed instead of computed tomography (CT) for further evaluation. The MRI showed an increase in the size of both kidneys, renal cortical heterogeneity and multiple cortical nodular lesions with diffusion restriction (constrained Brownian movement of water molecules) on diffusion-weighted MRI. A negative urine culture result in children presenting with fever and abdominal pain may mislead the clinicians, causing them to miss a nephro-urological diagnosis. It is therefore recommended that patients in whom the cause of fever cannot be determined be scanned by ultrasound and examined by CT or MRI so that undiagnosed and/or suspected cases of AFBN might be detected.