Residency · Residency · Diagnostic Radiology
Breast MRI: Indications and Interpretation
Introduction
Breast MRI is a highly sensitive imaging modality used as an adjunct to mammography and ultrasound. It leverages dynamic contrast-enhanced (DCE) sequences to evaluate breast lesions based on morphology and enhancement kinetics. Understanding appropriate indications and systematic interpretation is essential for the diagnostic radiology resident.
Physics and Technical Considerations
Pulse Sequences
T1-weighted pre- and post-contrast sequences form the backbone of breast MRI. T2-weighted sequences help differentiate cysts from solid lesions, while diffusion-weighted imaging (DWI) provides complementary information, with low ADC values suggesting malignancy. Short tau inversion recovery (STIR) or fat-suppressed T2 sequences aid in fluid characterization. Temporal resolution should be approximately 60-120 seconds per acquisition to capture kinetic data.
Contrast Kinetics
| Kinetic Curve Type | Pattern | Significance |
|---|---|---|
| Type I (Persistent) | Progressive enhancement | Favors benign |
| Type II (Plateau) | Rapid rise then levels off | Indeterminate |
| Type III (Washout) | Rapid rise then decline | Suspicious for malignancy |
A Type I curve (persistent) shows progressive enhancement and favors a benign etiology. A Type II curve (plateau) is indeterminate and requires morphologic correlation. A Type III curve (washout) shows rapid early enhancement followed by a decline and is suspicious for malignancy. Maximum intensity projection (MIP) images provide an overview of enhancing lesions.
Indications for Breast MRI
Screening Indications
Breast MRI screening is indicated for women with a lifetime risk greater than 20%, including BRCA1/2 carriers and those with Li-Fraumeni or Cowden syndrome. It is also recommended for women with a history of chest wall radiation between ages 10 and 30 (such as for Hodgkin lymphoma treatment) and for first-degree relatives of known BRCA carriers, even if untested.
Diagnostic Indications
Diagnostic breast MRI is used for extent of disease evaluation in newly diagnosed breast cancer, evaluation of the contralateral breast at diagnosis, assessment of treatment response to neoadjuvant chemotherapy, and workup of occult primary breast cancer when axillary nodal metastasis is present but mammography and ultrasound are negative. Additional indications include evaluation of silicone implant integrity using silicone-specific sequences and problem solving when mammography and ultrasound are inconclusive.
BI-RADS MRI Lexicon
Mass Descriptors
Masses are described by shape (oval, round, irregular), margin (circumscribed, irregular, spiculated), and internal enhancement pattern (homogeneous, heterogeneous, rim enhancement, dark internal septations).
Non-Mass Enhancement (NME)
Non-mass enhancement is described by its distribution (focal, linear, segmental, regional, multiple regions, diffuse) and its internal enhancement pattern (homogeneous, heterogeneous, clumped, clustered ring). Segmental clumped NME is highly suspicious for ductal carcinoma in situ (DCIS).
Background Parenchymal Enhancement (BPE)
BPE is classified as minimal, mild, moderate, or marked. Ideally, breast MRI should be performed on days 7-14 of the menstrual cycle to minimize BPE, as marked BPE can obscure lesions and reduce sensitivity.
Interpretation and Reporting
Systematic Approach
The interpretation should begin with comparison to prior mammograms and ultrasounds. Morphology is evaluated first, followed by kinetics. The radiologist assesses for skin thickening, chest wall invasion, and axillary lymphadenopathy and reports findings using standardized BI-RADS assessment categories (0-6). Enhancing lesions should be correlated with second-look targeted ultrasound for potential biopsy.
MRI-Guided Biopsy
MRI-guided biopsy is indicated when a lesion is visible only on MRI and cannot be identified on second-look ultrasound. The procedure is performed with the patient prone using a grid or freehand technique, and post-biopsy clip placement is essential for future localization.
Common Pitfalls
False positives can occur with fibroadenomas, fat necrosis, and hormonal enhancement, all of which can mimic malignancy. False negatives may occur with low-grade DCIS and mucinous carcinoma, which may show minimal enhancement. Inadequate fat suppression can obscure enhancing lesions, and motion artifact degrades both image quality and kinetic analysis.
Clinical Pearls
Breast MRI has a sensitivity of approximately 95-100% for invasive cancer but lower specificity (around 70%). MRI findings should always be correlated with mammography and ultrasound before recommending biopsy. Timing breast MRI to the second week of the menstrual cycle reduces background enhancement and false positives. Implant evaluation requires dedicated silicone-sensitive sequences that use water suppression rather than fat suppression. The linguine sign and subcapsular line sign on MRI indicate intracapsular silicone implant rupture.
References
- Mann RM, Cho N, Moy L. Breast MRI: State of the Art. Radiology. 2019;292(3):520-536.
- Morris EA, et al. ACR BI-RADS Magnetic Resonance Imaging. In: ACR BI-RADS Atlas. 5th ed. American College of Radiology; 2013.
- Saslow D, et al. American Cancer Society Guidelines for Breast Screening with MRI as an Adjunct to Mammography. CA Cancer J Clin. 2007;57(2):75-89.
- Kuhl CK. The Changing World of Breast Cancer Management: MRI. J Clin Oncol. 2021;39(21):2356-2364.