Breast MRI — Extra-Mammary Findings
Distant Metastasis Sites
Most common sites of distant breast cancer metastasis (seen on breast MRI):
| Site | Frequency |
|---|---|
| Bone | 57.5% |
| Lung | 36.1% |
| Liver | 34% |
| Lymph nodes | 27% |
| Brain | 34.5% |
High PPV for malignancy: Abnormal lesions in bone, lung, and lymph nodes. Low PPV for malignancy: Liver lesions, pleural lesions, pericardial effusions (all commonly benign).
Board Pearl
Bone mets are the most common distant metastasis from breast cancer (57.5%). Median survival with bone mets: 33 months. Triple negative cancer (basal-type especially) has less propensity to go to bones (though still can).
Bone Metastases
- Most common distant metastasis from breast cancer
- Median survival: 33 months
- TNBC (basal-type) has less bone propensity
- Sternum, manubrium, xiphoid, ribs, and vertebrae are commonly imaged on breast MRI
- Hemangiomas: common diagnostic dilemma on MRI
- Women with history of osteoporosis or on hormone blockers → more prone to osteoporotic fractures (not mets)
Lung Findings
- Median survival with lung mets: 22 months
- Radiation pneumonitis (on the radiated side):
- Starts 4–6 weeks after radiation
- Peaks 3–4 months
- Stabilizes 9–12 months with radiation-induced fibrosis
- Any increase in lung abnormality after 1–2 years → suspicious for infection or malignancy
- Incidental dependent atelectasis: commonly seen in prone MRI positioning
Pleural/Pericardial Effusions
- Usually have a low PPV for malignancy → most are physiologic
- Physiologic effusions: very small and bilateral
- Malignant effusions: more commonly unilateral, often moderate-to-large in size; right more common than left
- A moderate unilateral effusion in a patient with history of breast cancer → needs further workup
Liver Findings
- Mets and hemangiomas are the most common solid lesions in the liver
- Hemangiomas: look for typical enhancement pattern (peripheral nodular, fills in); often not seen on breast MRI
- Incidentally noted liver lesions on breast MRI have a low PPV for malignancy
- Cystic lesions: often biliary hamartomas (Von Meyenburg complexes)
- Hepatosteatosis: look for diffuse changes; MRI — if liver is more hyperintense than spleen on pre-T1 → likely steatotic
- Pseudocirrhosis: unique complication of chemotherapy for diffuse liver mets from breast cancer
- Capsular retraction mimicking cirrhosis
- Can get portal hypertension
- Not as common as true cirrhosis
Lymph Nodes (Staging Implications)
Regional Lymph Nodes (for staging)
- Ipsilateral axillary (Levels I, II, III), internal mammary, supraclavicular, infraclavicular
- Intramammary LNs = classified as axillary nodes for staging purposes
- Rotter nodes (interpectoral) often not taken on Level I/II dissection → important to evaluate on MRI
Distant Disease (M1)
Any lymph node involvement outside ipsilateral regional nodes = M1 disease:
- Mediastinal
- Hilar
- Cervical
- Contralateral axillary
- Distant LN involvement: median survival 43 months
Non-Ipsilateral Lymph Node Involvement
- Worsens prognosis
- Mediastinal nodes have high PPV for malignancy
- Hard to see due to surrounding structures and respiratory motion
Chest Wall and Skin Involvement
Pectoralis Muscle Enhancement
- Muscle will enhance abnormally with edema — does NOT change the stage
- Does NOT qualify as chest wall involvement
- Patient still gets radical mastectomy with pec major and minor removals
Chest Wall Invasion (T4a)
- Definition: involvement of serratus anterior, intercostals, or ribs
- Stage IIIB regardless of primary tumor size
Skin Involvement (T4b) — at least Stage IIIB
- Skin involvement including ulceration or skin nodules = T4 disease
- Makes skin-sparing procedures not possible
- Median survival: 43 months
- Enhancing skin lesions: usually epidermal inclusion or sebaceous cysts; but if patient has history of cancer (breast or melanoma especially) → pay careful attention
Diffuse Skin Thickening
- Often with an underlying mass
- May represent inflammatory breast cancer — pathology shows diffuse tumor emboli in dermal lymphatics
- At least Stage IIIB
Cardiac Findings
Look at the heart on breast MRI:
- Cardiomegaly
- Great vessel orientation
- Dextrocardia
- Aortic course/diameter (look sagittal)
GI Findings
- Hiatal hernia: commonly seen on breast MRI
- Peritoneal and adrenal involvement: not infrequently seen with ILC metastases
- GI involvement by breast cancer mets is rare overall, but ILC > other types
Differential Diagnosis: Regional Lymph Node Findings
| Region | Cause |
|---|---|
| Cortical thickening | Metastasis (first in cortex, under capsule) |
| Fatty hilum replaced | Metastasis |
| Round, avascular | Metastasis |