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Small Masses on Breast MR

Posted Mar 31, 2012 Updated Apr 10, 2023
By Sughra Raza MD , Meera Sekar MD , Eugene M.W. Ong MBBS , Robyn L. Birdwell MD
9 min read

Rationale and Objectives

To evaluate outcome of magnetic resonance (MR)-detected biopsied breast lesions ≤5 mm by correlating imaging characteristics with pathology.

Methods and Materials

Institutional review board–approved retrospective review of 565 lesions biopsied with MR guidance between March 2004 and February 2009 found 68 lesions ≤5 mm in 61 patients. Lesions evaluated were those prospectively recommended for biopsy based on clinical setting, suspicious lesion morphology, and kinetics. Two study radiologists, blinded to final pathology, reviewed MR exams recording patient age, exam indication (staging, surveillance, diagnostic, or follow-up), mass location, size, morphology, T2-weighted signal, and kinetics. Chart review provided final pathology.

Results

Of 68 masses ≤5 mm, 14 (20.6%) were malignant. Of 32 <5 mm, 32 (28.1%) were malignant. Of 14 malignancies, 7 (50%) were in patients with recently diagnosed breast cancer, 6 in the same breast, of which 4 (66.7%) were in same quadrant. Higher likelihood of malignancy based on proximity to known cancer was statistically significant ( P = .01). No significant difference in proportion of malignancies was found based on age, T2-weighted signal, morphology, or kinetics.

Conclusion

For MR-detected biopsied masses, the positive predictive value for malignancy of those ≤5 mm was 20.6%. The highest prevalence of cancers was in the same quadrant as a newly diagnosed breast cancer. The decision to biopsy small masses should be based on carefully assessed MR features, and in the context of exam indication, not solely on size.

For the breast imaging radiologist interpreting magnetic resonance (MR) exams, assessment of very small enhancing lesions is challenging. Patients with newly diagnosed breast cancer (staging) or at high risk for breast cancer are more likely to have malignant lesions and benefit from the heightened sensitivity of breast MR imaging (MRI) . Specific to the breast, the American College of Radiology (ACR) Breast Imaging Reporting and Data System (BI-RADS) lexicon for breast MRI defines as “focus” any dot of enhancement that is too small for further characterization, generally <5 mm in size. Although in some cases a focus may be a solitary finding, the appearance of multiple foci can be a manifestation of physiologic background parenchymal enhancement. In such cases, distinguishing a small mass (characterizable shape and margins) within this background can be challenging.

A 2001 study found little utility in sampling breast lesions <1 cm because of the high likelihood of inconclusive results. A study in 2006 showed <3% malignancy in masses <5 mm and suggested that such lesions be managed with short interval imaging follow-up. Van den Bosch found 11 malignancies among 30 MR-detected ≤5 mm lesions corresponding to a malignancy rate of 37%. To identify which features might have led to the biopsy recommendation in these small masses, Daniel et al reevaluated 19 of Van den Bosch’s 30 cases, comparing the morphologic and kinetic features to an age-controlled cohort of larger, more easily characterized masses. They found that the morphology and kinetics of small masses can be assessed in a manner similar to larger masses. In 2010 Dietzel et al found in their retrospective review (12 years of data), 88 MR-detected ≤5 mm lesions, 31% of which were malignant.

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Materials and methods

Study Population

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Breast MRI Technique

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MR-guided Biopsy Technique

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Data Collection and Analysis

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Figure 1, A 38 year old with right bloody nipple discharge and microcalcifications was found to have ductal carcinoma in situ (DCIS). T2W sagittal image from a staging magnetic resonance imaging scan shows biopsy clip artifact ( a, bold arrow ) and a small intermediate T2 signal mass posteriorly. On dynamic contrast enhanced image, this 4-mm mass shows irregular margins ( b,c; arrow ) with washout kinetics ( d, arrow ). Kinetics are better seen on CAD angiomap ( e, arrow ). Pathology was invasive ductal carcinoma with DCIS.

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Results

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Age

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Table 1

Size and Age

Lesion (Number of Patients) Age, Years

Mean (Range) Size, mm

Mean (Range) All (68) 52.8 (26–82) 4.4 (3–5) Malignant (14) 56.5 (37–82) 4.1 (3–5) Benign (54) 51.8 (26–81) 4.5 (3–5)

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Indication for MRI

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Table 2

Indication for Magnetic Resonance Imaging

Indication for Magnetic Resonance Malignant Benign Total_P_ Staging 7 18 25 .35 Surveillance 1 15 16 .16 Follow up of prior magnetic resonance findings 1 2 3 .5 Diagnostic 5 19 24 1.00

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Basis for Biopsy Recommendation

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Location

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Table 3

Proximity to Recently Diagnosed Cancer

Location of Known Cancer PPV of Malignancy in Index Lesion_P_ Contralateral 16.7% 1 Ipsilateral 27.8% 1 Same quadrant 44.4% .01

PPV, positive predictive value.

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Size

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Morphology

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T2W Signal

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Delayed Enhancement Kinetics

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Pathology and Feature Analysis

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Discussion

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Indications for MRI

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Figure 2, A 66 year old with history of bilateral risk lesions. Six-month follow-up magnetic resonance imaging for a 6-mm smooth right upper breast mass now shows margins to be slightly irregular ( a,b: dynamic sagittal, arrow ) with plateau kinetics ( c: delayed axial, arrow ). Also seen is a 3 mm focus in inferior breast ( d: sagittal dynamic, e: delayed axial, arrows ) to be managed depending on pathology of upper mass. MRI guided core needle biopsy of the 6 mm mass showed invasive lobular carcinoma. Subsequent biopsy of the 3 mm focus showed invasive ductal carcinoma.

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Basis for Biopsy Recommendation

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Location of Small Masses Relative to Existing Cancer

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Figure 3, A 50 year old with newly diagnosed invasive ductal carcinoma and ductal carcinoma in situ (DCIS). Dynamic series of the staging magnetic resonance imaging shows the primary cancer on the delayed sagittal image ( a, arrow ), and a 4-mm oval mass with irregular margins on the dynamic axial ( b,c; arrow ) and plateau kinetics ( d, arrow ) in the upper outer quadrant. Pathology of the small mass was IDC with DCIS.

Figure 4, A 37 year old with newly diagnosed left invasive ductal carcinoma. Dynamic images show the >3 cm cancer in the left upper breast ( a, arrow ), and a contralateral right 5-mm rapidly enhancing mass ( b,c; arrow ) with washout kinetics ( d, arrow ). Kinetics are better demonstrated on the computer-assisted diagnosis angiomap images of contiguous slices ( e, arrows ). Pathology showed invasive ductal carcinoma with ductal carcinoma in situ identical to the contralateral cancer.

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Size

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Morphology

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Delayed Enhancement Kinetics

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Conclusions

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References

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Academic Radiology, Volume 19, Issue 4
Journals General Radiology
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