False-positive helical CT findings of multifocal and multicentric breast cancer: is attenuation of tumor useful for diagnosing enhanced lesions?

OBJECTIVE

To analyze helical CT false-positive multifocal breast cancers and to assess the relevance of the attenuation of tumors for diagnosing enhanced lesions.

METHODS

Helical CT studies of 156 invasive breast cancers before breast conserving surgery were examined. A lesion was defined as positive if focal enhancement was detected by CT within 100 seconds after contrast material administration. The attenuation and enhancement percent ratio [(post-contrast value/pre-contrast value)%] were obtained. Attenuation of false-positive and malignant lesions was compared.

RESULTS

Helical CT enabled the detection of all 156 invasive tumors with 95 intraductal tumor extensions. The sensitivity and specificity of multifocal/multicentric disease detection by helical CT were 69% and 90%, respectively. False-positive multifocal/multicentric findings were obtained in 11 (7%) of 156 cases. The mean value of the enhancement percent ratio of the index tumors was 237%. Significant differences in the attenuation on post-contrast enhanced scans between the enhanced lesions (index tumors; mean, 82 HU), the true-positive multifocal/multicentric lesions (mean, 73 HU), the false-positive multifocal/multicentric lesions (mean, 87 HU) and normal breast tissue (mean, 32 HU) were found (p<0.0001). The attenuation of the true-positive multifocal/multicentric lesions on post-contrast enhanced scans was significantly less than that of the false-positive multifocal/multicentric lesions (p=0.03).

CONCLUSION

Attenuation of tumor is not useful for differential diagnosis of enhanced lesions on helical CT of the breast. The presence of enhancement alone does not always indicate a malignant lesion.