Images of Memorable Cases: Case 18 Plain abdominal radiographs of a 72-year-old man with fever, chills, dysuria, and right flank pain. Urinalysis showed proteinuria, pyuria, and gram-negative rods. 18. Perinephric abscess In a patient thought to have acute pyelonephritis, the presence of air encircling the kidney is pathognomonic of perinephric abscess. Drainage of this patient’s abscess yielded purulent material containing Proteus mirabilis.