URINARY-BLADDER PSEUDOLESIONS ON CONTRAST-ENHANCED HELICAL CT - FREQUENCY AND CLINICAL IMPLICATIONS

OBJECTIVE. The goals of this study were to define the distinguishing c haracteristics and frequency of urinary bladder pseudolesions that are produced as opacified urine enters the bladder during contrast-enhanc ed helical CT of the abdomen and to evaluate the usefulness of delayed imaging in differentiating pseudolesions from true lesions. SUBJECTS AND METHODS. Contrast-enhanced routine CT scans of 184 patients were o btained prospectively. For each patient, we also obtained 5-min delaye d images of the bladder. The images were evaluated for apparent focal thickening or polypoid lesions involving the bladder wall, findings th at may represent bladder neoplasia, without knowledge of the indicatio ns for the scan, the patient's clinical history, or the patient's diag nosis. Apparent lesions that were visible on routine images and entire ly absent on delayed images were considered to be pseudolesions. RESUL TS. Apparent lesions were identified on 20 (10.9% =/- 4.5% [limits of the 95% confidence interval]) of the routine CT scans. Using delayed i mages, the 21 apparent lesions in these 20 patients were resolved as 1 3 pseudolesions and eight true lesions. Pseudolesions were present in 6.5% +/- 3.6% of patients. CONCLUSION. Pseudolesions of the bladder th at are indistinguishable from true lesions pose a significant clinical problem in routine contrast-enhanced helical CT of the abdomen. Delay ed imaging of the bladder is useful in distinguishing pseudolesions fr om true lesions.