Revisiting Nonmass Enhancement in Breast MRI: Analysis of Outcomes and Follow-Up Using the Updated BI-RADS Atlas

OBJECTIVE. The purpose of this study is to assess the frequency of reclassification of nonmass enhancement (NME) as background parenchymal enhancement (BPE) and to determine positive predictive values (PPVs) of NME descriptors using the revised BI-RADS atlas. MATERIALS AND METHODS. A retrospective review of our institution's MRI database from January 1, 2009, through March 30, 2012, identified 6220 contrast-enhanced breast MRI examinations. All findings prospectively assessed as NME and rated as BI-RADS categories 3, 4, and 5 (n = 386) were rereviewed in consensus by two radiologists who were blinded to pathologic findings with the fifth edition of the BI-RADS lexicon. Findings considered as postsurgical, associated with known cancers, NME given a BI-RADS category 3 assessment before 2009, previously biopsied, and those reclassified as BPE, focus, or mass were excluded (n = 181). Medical records were reviewed for demographics and outcomes. RESULTS. Two hundred five women were included (mean age, 48.8 years; range, 21-84 years). Seventy-seven of 386 findings (20.0%) were reclassified as BPE, and patients with BPE were younger than those with NME (mean age, 43.9 years; range, 31-62 years) (p = 0.003). Pathology results for 144 of 205 (70.2%) patients included 52 malignant, 11 high-risk, and 81 benign lesions. The highest PPVs for distribution patterns were 34.5% (10/29) for segmental and 100.0% (3/3) for diffuse distribution. The highest PPVs for internal enhancement patterns were 36.7% (11/30) for clustered ring enhancement and 27.5% (11/40) for clumped enhancement. No difference for NME malignancy rate was noted according to BPE (10/52 [19.2%] marked or moderate; 42/153 [27.5%] mild or minimal, p = 0.24). Thirty-two percent (17/52) of malignant NMEs had high T2 signal. CONCLUSION. Careful assessment of findings as BPE versus NME can improve PPVs, particularly in younger women. Although clustered ring enhancement had one of the study's highest PPVs, this number falls below previously published rates. Reliance on T2 signal as a benign feature may be misleading, because one-third of malignancies had T2 signal.