Sensitivity of sonography in pyonephrosis: a reevaluation.

OFF sonographic features distinguishing randomly selected cases of simple hydronephrosis (34 patients) from pyonephrosis (16 patients) were reviewed in 50 patients. Fluid-fluid levels and coarse medium-intensity echoes within the renal collecting system were highly reliable findings for pyonephrosis in 10 patients. However, in six patients with proven pyonephrosis, the renal collecting system either was anechoic (four patients) or contained low-level echoes (two) that were difficult to distinguish from artifacts. Although the specificity for diagnosing pyonephrosis was 100%, the sensitivity was only 62%. Because of the consequences of misdiagnosis, sonographically guided diagnostic needle aspiration may still be required in patients with urosepsis and significant hydronephrosis.