Morphology takes precedence over kinetics. Kinetics most useful for mass lesions — less reliable for non-mass enhancement. A morphologically suspicious mass with persistent kinetics still requires biopsy.
MRI Lexicon — Masses
Shape
| Descriptor | Implication |
|---|---|
| Oval / Round | Favors benign — fibroadenoma, cyst, lymph node |
| Irregular | Suspicious — malignancy |
Margin
| Descriptor | Implication |
|---|---|
| Smooth / Circumscribed | Favors benign |
| Irregular / Spiculated | Suspicious — malignancy |
Internal Enhancement
| Descriptor | Implication |
|---|---|
| Homogeneous | Uniform; non-specific — can be benign or malignant |
| Heterogeneous | Irregular internal enhancement — suspicious |
| Rim enhancement | Most suspicious internal pattern — associated with IDC, central necrosis |
| Dark internal septations (T2-hypointense) | Strongly favors benign fibroadenoma |
| Enhancing internal septations | Suspicious — more concerning than non-enhancing septations |
MRI Lexicon — Non-Mass Enhancement (NME)
Distribution
| Descriptor | Implication |
|---|---|
| Focal | Occupies <25% of a quadrant; BI-RADS depends on internal pattern |
| Linear | Arrayed in a line — suggests ductal involvement; suspicious |
| Segmental | Triangular toward nipple, in a duct and branches — most suspicious NME distribution; DCIS until proven otherwise |
| Regional | Large area, not conforming to ductal distribution; variable risk |
| Multiple regions | Two or more large regions; often bilateral — may reflect BPE |
| Diffuse | Throughout entire breast — typically BPE; bilateral |
Internal Pattern
| Descriptor | Implication |
|---|---|
| Homogeneous | Uniform; can be BPE or malignant |
| Heterogeneous | Variable; non-specific |
| Clumped | Cobblestone appearance; suspicious, particularly in segmental distribution |
| Clustered ring | Most suspicious NME internal pattern — rim-enhancing foci within NME; associated with high-grade DCIS |
Segmental NME + clustered ring internal pattern = highest suspicion for DCIS. Even with a benign biopsy result, this combination is almost always discordant and requires repeat sampling or surgical excision.
DCE Kinetics
| Phase | Type | Signal Change | Implication |
|---|---|---|---|
| Initial (first 1–2 min) | Slow | <50% signal increase | Less suspicious |
| Initial | Medium | 50–100% signal increase | Intermediate |
| Initial | Fast (rapid) | >100% signal increase | More suspicious |
| Delayed | Type I — Persistent | Continues to increase over time | Favors benign (fibroadenoma, fibrocystic change, BPE) |
| Delayed | Type II — Plateau | Signal stabilizes after initial enhancement | Intermediate; overlap between benign and malignant |
| Delayed | Type III — Washout | Signal decreases after peak | Most suspicious — ~87% PPV for invasive malignancy in mass lesions |
Background Parenchymal Enhancement (BPE)
| BPE Level | Description | Clinical Impact |
|---|---|---|
| Minimal | Enhancement of only a few scattered foci | Highest sensitivity for lesion detection |
| Mild | Enhancement of <¼ of fibroglandular tissue | Good sensitivity; slight background |
| Moderate | Enhancement of ¼–½ of fibroglandular tissue | Reduced sensitivity; can obscure lesions |
| Marked | Enhancement of >½ of fibroglandular tissue | Most limited sensitivity; consider repeat in follicular phase |
Timing optimization: For premenopausal patients, schedule breast MRI on days 7–14 of the menstrual cycle (follicular phase) to minimize BPE. Avoid days 1–7 and the luteal phase. Postmenopausal women on HRT may have elevated BPE — consider temporary cessation before high-risk screening MRI if clinically feasible.
MRI Indications
| Indication | Details |
|---|---|
| High-risk screening | ≥20% lifetime risk: BRCA1/2, strong family history, prior chest RT ≥30 Gy before age 30, untested first-degree relative of BRCA carrier, Li-Fraumeni, Cowden, Bannayan-Riley-Ruvalcaba syndromes |
| Extent of disease | Newly diagnosed breast cancer — evaluate ipsilateral breast for multifocal/multicentric disease and contralateral breast. Particularly valuable in lobular carcinoma (often mammographically occult). |
| Occult primary | Axillary nodal metastasis with unknown primary; negative mammogram and US. MRI detects primary in ~75% of cases. |
| Neoadjuvant monitoring | Assess tumor response to neoadjuvant chemotherapy — most accurate modality for residual disease (though pathologic CR can be overstated). |
| Post-surgical scar vs. recurrence | Scar shows no enhancement after 18 months post-surgery; recurrence shows enhancement with washout kinetics. Minimum 6–12 months post-surgery before reliable interpretation. |
| Implant evaluation | Gold standard for silicone implant rupture. "Linguine sign" = intracapsular rupture; extracapsular silicone is direct evidence. No IV contrast required. |
| Dense breasts / supplemental screening | Annual MRI preferred supplemental tool for high-risk dense-breast patients. Abbreviated MRI (AB-MRI) emerging for intermediate-risk patients. |
MRI does NOT replace mammography. Mammography is superior for calcification detection — calcifications are often the only manifestation of DCIS and may be MRI-occult. Combined annual MRI + mammography (staggered 6 months apart) is the standard for high-risk screening — not MRI alone.