Performance of DWI as a Rapid Unenhanced Technique for Detecting Mammographically Occult Breast Cancer in Elevated-Risk Women With Dense Breasts

Abstract

Objective: The objective of our study was to evaluate the performance of DWI to detect mammographically occult breast cancer in elevated-risk women with dense breasts.

Materials and methods: We retrospectively reviewed all women who underwent screening breast MRI at our institution from January 2007 through May 2013. We created a case-control cohort composed of 48 subjects with mammographically dense breasts: 24 with mammographically occult cancer detected on MRI and 24 healthy women with negative MRI findings who were matched to the subjects with breast cancer patients for age, breast density, and MRI protocol. The contrast-to-noise ratio (CNR), apparent diffusion coefficient (ADC), and conspicuity score (range, 1-5) were assessed on DWI for all malignancies. Lesions and normal tissue were compared using the Wilcoxon signed rank test; associations with clinical characteristics were evaluated using the Mann-Whitney U test. Three experienced breast imagers who were blinded to medical records and contrast-enhanced MRI findings independently evaluated the unenhanced MRI scans of the 48 women for the presence of cancer.

Results: Mammographically occult breast cancers (invasive carcinoma, n = 16; ductal carcinoma in situ, n = 8) in women with dense breasts typically exhibited higher signal intensity on DWI than normal parenchyma (median CNR of cancers, 1.4; median conspicuity score of cancers, 4) and a lower ADC (median, 1.31 vs 1.79 × 10(-3) mm(2)/s, respectively) (p < 0.0001). The conspicuity score, CNR, and ADC were not associated with patient age, menopausal status, lesion size, morphologic type, or histology (p > 0.05). Average reader performance using unenhanced MRI was 45% sensitivity, 91% specificity, 62% positive predictive value, and 83% negative predictive value.

Conclusion: In elevated-risk women with dense breasts, DWI can reveal cancers in addition to those detected on mammography alone with a low false-positive rate; these results suggest that DWI may have potential as a rapid supplemental screening tool.

Keywords: DWI; MRI; breast cancer screening; cancer detection; dense breasts; mammographically occult cancer; reader performance.

Fig. 1—

Flowchart shows algorithm for DWI reader interpretation. Readers first evaluated images for unique area of high signal intensity on DWI. If no unique area of high signal intensity was present, study was reported as negative. If study was positive for unique high-signal-intensity area on DWI, reader categorized finding as mass or nonmass. If mass, reader evaluated T2-weighted sequence to determine whether any of following findings were present: round or oval shape, circumscribed margins, and homogeneously bright signal intensity. If mass met all of these criteria, it was reported as benign and classified as negative. If mass did not meet all of these criteria, reader assessed corresponding apparent diffusion coefficient (ADC) map. If mass was visually bright on ADC map (representing high diffusivity), it was reported as benign and classified as negative; if mass was dark on ADC map (representing low diffusivity), it was reported as positive. If finding was nonmass lesion, reader assessed ADC map as follows: If nonmass lesion was bright on ADC map, it was reported as benign and categorized as negative; if nonmass lesion was dark on ADC map, it was reported as positive. As general rule, ADC value of ≤ 1.8 × 10⁻³ mm²/s was considered suspicious for malignancy.

Fig. 2—

58-year-old woman with dense breasts and mammographically occult invasive ductal carcinoma. This patient underwent high-risk screening MRI (3 T) because of personal history of right breast cancer. A and B, Dynamic contrast-enhanced MR image (A) and DW image (B) show 5-mm mass (arrow). Mass was categorized as high conspicuity on DWI (mean conspicuity score = 4 of 5).

Fig. 3—

58-year-old woman with dense breasts and mammographically occult malignant phyllodes tumor. Patient underwent high-risk screening MRI (3 T) because of strong family history of breast cancer. A and B, Dynamic contrast-enhanced MR image (A) and DW image (B) show 13-mm mass (arrow). Mass was categorized as very high conspicuity on DWI (mean conspicuity score = 5 of 5).

Fig. 4—

68-year-old woman with dense breasts and mammographically occult invasive ductal carcinoma. This patient underwent high-risk screening MRI (3 T) because of personal history of breast cancer. A and B, Dynamic contrast-enhanced MR image (A) and DW image (B) show 5-mm mass (arrow). Mass was categorized as very low conspicuity on DWI (mean conspicuity score = 1 of 5).

Fig. 5—

Comparison of quantitative and qualitative features of breast lesions on DWI. A, Graph shows that visually distinguishable lesions (conspicuity score ≥ 3; n = 16) tended to show higher contrast-to-noise ratio (CNR) on DWl than those that were not distinguishable (conspicuity score < 3; n = 8). Median CNR was 1.9 for visually distinguishable lesions versus 1.2 for lesions that were not distinguishable (p = 0.07). Upper and lower limits of boxes show 25th and 75th percentiles, respectively, and horizontal lines in middle of boxes show medians. Whiskers show range (minimum and maximum). B, Graph shows that visually distinguishable lesions also tended to have lower apparent diffusion coefficient (ADC) values versus not distinguishable lesions, but difference was not significant. Median ADC is 1.26 × 10⁻³ mm²/s for visually distinguishable lesions versus 1.51 × 10⁻³ mm²/s for lesions that were not distinguishable (p = 0.11). Upper and lower limits of boxes show 25th and 75th percentiles, respectively, and horizontal lines in middle of boxes show medians. Whiskers show range (minimum and maximum).

Fig. 6—

58-year-old woman with dense breasts and mammographically occult invasive ductal carcinoma. Patient underwent high-risk screening MRI (3 T) because of strong family history of breast cancer. On DWI, this lesion received unblinded visual conspicuity score of 5 and was correctly identified in blinded reader study by two of three readers. A, Axial DW image (b value = 800 s/mm²) shows area of high signal intensity (arrow). B, Apparent diffusion coefficient (ADC) map shows low diffusivity of lesion (arrow). ADC value is 1.45 × 10⁻³ mm²/s. C, T1-weighted dynamic contrast-enhanced MR image (provided here for reference, not provided to readers) shows enhancing 8-mm mass (arrow).

Fig. 7—

74-year-old woman with dense breasts and mammographically occult high-grade ductal carcinoma in situ (DCIS). This patient underwent high-risk screening MRI (1.5 T) because of personal history of left breast cancer. On DWI, this lesion received unblinded visual conspicuity score of 4 and was correctly identified in blinded reader study by one of three readers. A, Axial DW image (b value = 600 s/mm²) shows nonmass area (arrow) is exhibiting high signal intensity. B, Apparent diffusion coefficient (ADC) map shows low diffusivity of nonmass area (arrow). ADC value was 0.83 × 10⁻³ mm²/s. C, T1-weighted dynamic contrast-enhanced MR image (provided for reference, not provided to readers) shows 12-mm nonmass enhancement (arrow).

Fig. 8—

49-year-old woman with dense breasts and benign mass. This patient underwent high-risk screening MRI (3 T) because of personal history of left breast cancer. On DWI, all three readers in blinded reader study correctly classified this breast as negative for malignancy. A, Axial DW image (b value = 800 s/mm²) shows mass with high signal intensity (arrow). B, T2-weighted fast spin-echo image shows mass (arrow) meets all three criteria to be judged benign lesion: It is oval, has circumscribed margins, and is homogeneously bright. C, Apparent diffusion coefficient (ADC) map shows high diffusivity of mass (arrow). ADC value is 2.11 × 10⁻³ mm²/s. D, Non-fat-suppressed T1-weighted fast gradient-echo image shows mass (arrow). E, T1-weighted dynamic contrast-enhanced MR image (provided for reference, not provided to readers) shows no enhancement in mass (arrow).

Fig. 9—

53-year-old woman with dense breasts and mammographically occult invasive ductal carcinoma. This patient underwent high-risk screening MRI (3 T) because of personal history of high-risk lesion in right breast. On DWI, this lesion received unblinded visual conspicuity score of 1.5 and was missed by all three readers in blinded reader study. A, Axial DW image (b value = 800 s/mm²) shows area of mildly elevated signal intensity (arrow). B. T2-weighted fast spin-echo image shows mass (arrow) is relatively isointense to normal fibroglandular tissue. C, Apparent diffusion coefficient (ADC) map shows low diffusivity of mass (arrow). ADC value is 1.48 × 10⁻³ mm²/s. D, Non-fat-suppressed T1-weighted fast gradient-echo image shows mass (arrow). E, Contrast-enhanced T1-weighted dynamic contrast-enhanced MR image (provided for reference, not provided to readers) shows 7-mm enhancing mass (arrow).

Fig. 10—

44-year-old woman with heterogeneously dense breasts. This patient underwent high-risk screening MRI (1.5 T) because of strong family history of breast cancer. On DWI, all three readers in blinded reader study incorrectly classified this breast as positive for malignancy. A, Axial DW image (b value = 800 s/mm²) shows focal mass (arrow) of elevated signal intensity identified by readers. B, T2-weighted fast spin-echo image shows mass (arrow) is isointense to normal fibroglandular tissue. 44-year-old woman with heterogeneously dense breasts. This patient underwent high-risk screening MRI (1.5 T) because of strong family history of breast cancer. On DWI, all three readers in blinded reader study incorrectly classified this breast as positive for malignancy. C, Apparent diffusion coefficient (ADC) map shows low diffusivity of mass (arrow). ADC value is 1.40 × 10⁻³ mm²/s. D, Non–fat-suppressed T1-weighted fast gradient-echo image shows mass (arrow). E, T1-weighted dynamic contrast-enhanced MR image (provided for reference, not provided to readers) shows enhancing oval mass (arrow) with circumscribed margins and dark internal septation. Mass was categorized as benign finding on clinical dynamic contrast-enhanced MRI interpretation and likely represents benign fibroadenoma.

Fig. 10—

44-year-old woman with heterogeneously dense breasts. This patient underwent high-risk screening MRI (1.5 T) because of strong family history of breast cancer. On DWI, all three readers in blinded reader study incorrectly classified this breast as positive for malignancy. A, Axial DW image (b value = 800 s/mm²) shows focal mass (arrow) of elevated signal intensity identified by readers. B, T2-weighted fast spin-echo image shows mass (arrow) is isointense to normal fibroglandular tissue. 44-year-old woman with heterogeneously dense breasts. This patient underwent high-risk screening MRI (1.5 T) because of strong family history of breast cancer. On DWI, all three readers in blinded reader study incorrectly classified this breast as positive for malignancy. C, Apparent diffusion coefficient (ADC) map shows low diffusivity of mass (arrow). ADC value is 1.40 × 10⁻³ mm²/s. D, Non–fat-suppressed T1-weighted fast gradient-echo image shows mass (arrow). E, T1-weighted dynamic contrast-enhanced MR image (provided for reference, not provided to readers) shows enhancing oval mass (arrow) with circumscribed margins and dark internal septation. Mass was categorized as benign finding on clinical dynamic contrast-enhanced MRI interpretation and likely represents benign fibroadenoma.

Fig. 11—

54-year-old woman with dense breasts. This patient underwent high-risk screening MRI (3 T) because of high genetic risk (Ashkenazi Jewish heritage) and history of atypia in right breast. On DWI, one reader in blinded reader study incorrectly classified right breast as positive for malignancy. A, Axial DW image (b value = 800 s/mm²) shows area (arrow) of highly elevated signal intensity in subareolar region of right breast that was identified by one reader. B, T2-weighted fast spin-echo image shows area (arrow) is isointense to adjacent fibroglandular tissue. C, Apparent diffusion coefficient (ADC) map shows corresponding low diffusivity of area (arrow). ADC value is 1.20 × 10⁻³ mm²/s. D, Non–fat-suppressed T1-weighted fast gradient-echo image shows nothing abnormal in area (arrow). Comparison of this image with anatomic T2-weighted and T1-weighted images suggests presence of susceptibility-based distortion on DWI in nipple region. This artifact, which is caused by summation of mismapped pixels, is common in breast DWI and may explain elevated signal intensity identified at edge of breast. E, T1-weighted dynamic contrast-enhanced MR image (provided for reference, not provided to readers) shows moderate but nonsuspicious background parenchymal enhancement (arrow).