Pseudohydronephrosis on noncontrast computed tomography.

Noncontrast renal computed tomography (CT) has been advocated for the evaluation of the poorly functioning or nonvisualized kidney. However, some conditions can mimic hydronephrosis on such scans, leading to a false positive diagnosis of renal obstruction; two entities include peripelvic cysts and subcapsular hematoma. Illustrative cases are presented. Close attention to attenuation values and basic renal anatomic configurations will usually elucidate the true nature of equivocal findings. However, when hydronephrosis is still suspected on noncontrast renal CT, postcontrast images should be obtained or the finding further evaluated with other radiographic modalities.