In the United States, urinary tract infections are the most common urologic condition, with approximately 7 million outpatient visits and 1 million emergency department visits per year. In adults, diagnosis relies on typical clinical presentations and abnormal laboratory markers. Imaging is required for those who fail to respond to treatment, have atypical clinical presentation, or have a potentially life-threatening condition. Urinary tract infections most commonly occur in the bladder and then migrate hematologically to the kidney, causing tubulointerstitial inflammation that involves the renal pelvis and renal parenchyma to form pyelonephritis. CT scan, enhancement and delayed enhancement are useful in the diagnosis of acute bacterial pyelonephritis, and CT is significantly better than conventional radiology and ultrasound in the diagnosis of emphysematous pyelonephritis. Yellow granulomatous pyelonephritis is a chronic granulomatous lesion caused by recurrent bacterial urinary tract infections. Although US is easy to diagnose this disease, CT can provide not only specific information but also evaluation of extrarenal lesions, which can help in surgical planning. A history of tuberculosis and repeated antibiotic use provides important diagnostic information for radiologists, as the kidney is the most common site of extrapulmonary TB. Even in the absence of a history of TB, the presence of pelvic funnel stenosis, renal papillary necrosis, intracortical hypodense masses, scarring, and calcification is diagnostic of renal TB. CT is the primary test for the diagnosis of yellow granulomatous pyelonephritis for two reasons: 1. In most cases, specific presentation is required to make a definitive diagnosis; 2. Planning for surgical procedures depends on an accurate assessment of the extent of extrarenal involvement. The presence of enlarged kidney volume, stones, shallow renal pelvis, enlarged calyces, and loss of perirenal fat gap strongly suggests yellow granulomatous pyelonephritis. Although the hypointense shadow in the renal pelvis suggests fluid accumulation, it is more reflective of diffuse infiltration of inflammation, and percutaneous nephrostomy is absolutely contraindicated at this time. Despite the appearance of enhancement at the edge of the lesion, renal function cannot be observed on CT films.