Pyelonephritis. Coloured axial computed tomography (CT) scan through the abdomen of a 54-year-old woman with renal cysts (in both kidneys) and diffuse pyelonephritis of the left kidney (lower right). The left kidney is enlarged and inflamed. this patient reported abdominal pain and fever. Pyelonephritis may be either acute or chronic. The acute form is usually caused when bacteria causing cystitis spread up the ureters from the bladder. This case is caused by an inflammatory syndrome producing elevated levels of c-reactive protein (CRP).