Serial sonographic findings during progression from acute pyelonephritis to renal abscess: a rare case report.

Renal abscess, accumulation of infective fluid in the kidney, is a rare pathology. Currently, no reports of the serial imaging changes of acute pyelonephritis (APN) progressing to renal abscess exist. We report clinical and serial sonographic findings of a patient with hyper-immunoglobulin E syndrome, a primary immunodeficiency, who developed APN that progressed to renal abscess. Renal ultrasonography revealed that echogenicity of infectious lesions dramatically changed from isoechoic to hyperechoic and to hypoechoic during progression. These findings are useful for differential diagnosis of APN, acute focal bacterial nephritis, and renal abscess.