RESUMEN
Acute focal bacterial nephritis (AFBN), synonymous with acute lobar nephronia (ALN) or focal pyelonephritis, is an inflammatory mass without liquefaction caused by severe acute bacterial infection of kidney. Unless treated effectively, progression to a renal abscees may ensue. Clinically, AFBN presents as acute pyelonephritis, and radiologically, as focal swelling or mass. The distinction between AFBN and renal abceess or even tumor may be confusing and difficult. Ultrasonography and computerized tomography(CT) aid in establishing the correct diagnosis. However, the appearance of AFBN on sonography and CT is by no means pathognomonic. Benign or malignant renal tumors may have a similar appearance. With the clinical history, a high index of suspicion, and follow-up studies after institution of medical treatment may further aid in the differentiation. Herein we report 2 cases of AFBN, which were presented as renal masses.