Computed tomography differentiation of pyelonephritis and renal infarction

Acute renal infarction and acute pyelonephritis can have identical clinical presentations. Most of the computed tomography findings seen in acute renal infarction are similar to those in acute pyelonephritis, except for the characteristic cortical rim sign seen in acute infarction. This finding differentiates these two disorders. This sign may be subtle and not appreciated unless searched for diligently with appropriate computed tomography imaging at varying window settings with particular attention to the subcapsular region.