The CT findings in a diabetic patient with flank pain are consistent with emphysematous pyelitis.

The lack of intraparenchymal air distinguishes this entity from emphysematous pyelonephritis, which carries a more grave prognosis and often requires surgical management.

 According to the Huang-Tseng CT classification system, this case can be classified as class 1.

CT is the best diagnostic modality for emphysematous pyelitis/pyelonephritis.