Focal bacterial nephritis (lobar nephronia) presenting as renal mass.

A focal infection of the kidney can cause a diagnostic dilemma by mimicking a neoplasm. We describe a case of focal bacterial nephritis (acute lobar nephronia) caused by Escherichia coli in which the diagnosis was confirmed only after surgical exploration. Although the patient had fever on admission, urine and blood cultures were negative and fine needle aspiration of the kidney could not rule out a well-differentiated carcinoma.