Developing Asymmetry Identified on Mammography: Correlation with Imaging Outcome and Pathologic Findings

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Abstract
OBJECTIVE. Developing asymmetry on mammography is a focal asymmetric deposit that has appeared or increased in size or conspicuity since a previous examination. We examined the frequency, imaging outcome, and pathologic significance of developing asymmetry. MATERIALS AND METHODS. This study was performed in a retrospective cohort manner. We searched for all cases of developing asymmetry consecutively entered in our mammography database from April 1985 to April 2005. We examined radiology records to determine whether sonography and MRI were used as adjunctive diagnostic tools and examined pathology records to determine tissue diagnosis. RESULTS. Developing asymmetry was present in 292 (0.16%) of 180,801 consecutive screening examinations and 32 (0.11%) of 27,330 consecutive diagnostic examinations. After exclusion for absent data, the study consisted of 281 screening and 30 diagnostic cases. In the 281 cases of screening-detected developing asymmetry, biopsy was recommended and was performed in 84 (29.9%) of the cases. Thirty-six cases of cancer were identified, resulting in a positive predictive value of 12.8%, obtained by division of the number of cases of cancers by the number of examinations with abnormal mammographic findings (PPV1), and a PPV2 of 42.9%, obtained by division of the number of cases of cancer by the number of mammographic examinations in which findings led to a recommendation for biopsy. Biopsy was recommended and performed in 26 (86.7%) of the 30 cases of diagnostic mammography. Eight cases of cancer were identified, resulting in a PPV1 of 26.7% and a PPV2 of 30.8%. Of the 44 cancers detected at screening and diagnostic mammography, 21 had available sonographic data. Five (23.8%) of these 21 cases of cancer had no correlate at sonographic examination. MRI was performed in only two cases, both with benign diagnoses. CONCLUSION. Developing asymmetry is an uncommon finding. When this sign is identified on screening and diagnostic mammography, the likelihood of malignancy is sufficiently high to justify recall and biopsy. Normal sonographic findings do not exclude malignancy in the case of developing asymmetry.