Pyelonephritis

Pyelonephritis is a bacterial infection of the kidney, typically resulting from bacteria ascending through the urinary tract from the bladder. Symptoms include flank pain, fever, chills, and painful or frequent urination. On ultrasound, the affected kidney may appear enlarged, with areas of decreased echogenicity representing edema, and the renal cortex may appear swollen and heterogeneous. Color Doppler may show either increased blood flow (hyperemia) or decreased flow in severely affected areas. The collecting system may appear thickened, and complications such as abscess formation, pyonephrosis (infected hydronephrosis), or renal scarring can be detected. While the diagnosis of pyelonephritis is primarily clinical, ultrasound is important for identifying obstruction, abscess, or other complications that would change management.