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Pyelonephritis is a serious upper urinary tract infection involving the renal pelvis and kidney parenchyma, most commonly caused by ascending bacterial infection from the lower urinary tract. It presents with fever, flank pain, and urinary symptoms, requiring prompt antibiotic treatment to prevent complications such as renal scarring or sepsis.
Pyelonephritis typically results from ascending infection where bacteria travel from the bladder through the ureters to reach the renal pelvis and kidney tissue. E. coli is the most common causative organism, with infection facilitated by factors such as vesicoureteral reflux, urinary obstruction, or immunocompromised states that impair normal host defenses.
Diagnosis is based on clinical presentation of fever, costovertebral angle tenderness, and urinary symptoms combined with urinalysis showing pyuria and bacteriuria, plus positive urine culture. Imaging with CT or ultrasound may be needed to rule out complications like abscess formation or underlying structural abnormalities, particularly in cases of recurrent infection or treatment failure.
Key imaging focus: Wedge-shaped hypoperfusion, perinephric stranding, abscess, obstructing stone