Breast MRI

Dr Tom Foster and Radswiki ◉ et al.

Breast MRI is the most sensitive method for detection of breast cancer. Depending on international health regulations, it is either applied for screening of women at high risk for developing breast cancer (e.g. BRCA1 and BRCA2 carriers), as an additional diagnostic test in pretherapeutic breast cancer staging, monitoring of primary systemic therapies and for solving problematic diagnostic situations where direct biopsy is not possible.

Editorial board note: this article is probably outdated, lacks structure and is in need of a major rewrite. If you are interested in refining it you are more than welcome.

focus (formerly defined as <5 mm): enhancement too small to be characterized, should be considered as BPE if symmetric and multiple
mass enhancement (space occupying lesion, best diagnostic clue: margins can be assessed)
- shape: round (non-specific), oval (rather benign), irregular (rather suspicious)
- margins: circumscribed (benign), non-circumscribed (rather suspicious), spiculated (highly suspicious)
- internal enhancement pattern: homogeneous (rather benign), heterogeneous (non-specific), rim (rather suspicious, in particular, if centripetal, filling up over time), dark internal septations (rather benign), old BI-RADS included central enhancement (part of the lesion enhances, highly specific for fibroadenoma)
non-mass enhancement (best diagnostic clue: margins cannot be assessed due to diffuse enhancement or grouped multiple spots; non-mass are far more difficult to distinguish and reflect different pathological entities)
- distribution pattern: focal, linear (rather suspicious), regional, multiple regional, segmental (rather suspicious)
- internal enhancement pattern: homogeneous (rather benign), heterogeneous (non-specific), clumped (rather suspicious), clustered ring (rather suspicious, seldom seen), old BI-RADS included stippled, a homogeneous grainy enhancement typically benign
in all lesions: enhancement kinetics: see breast MRI enhancement curves
- washout (rather suspicious), plateau (non-specific), persistent (rather benign) (caveat: lymph nodes show washout but typical morphology)

MRI BI-RADS assessment categories

BIRADS 0: incomplete/non-diagnostic - this category should not be used for marked background parenchymal enhancement (BPE), motion artifacts etc.
BIRADS I: negative (no enhancing lesions, no benign changes such as scars, cysts etc.)
BIRADS II: benign (lymph nodes, inflamed cysts, fibroadenoma, fat necrosis, foci/stippled enhancement, patchy BPE).
BIRADS III: probably benign, requiring short term follow-up in 6 months. If the finding is visible on e.g. US, the most widely available method should be used for follow-up (should be applied only to lesions not fitting category II and IV, probably benign findings in high-risk screening should rather be biopsied than followed-up)
BIRADS IV: suspicious finding requiring biopsy (biopsy should always be tried by US first as the majority of MRI lesions can be localized by targeted ultrasound)
BIRADS V: highly suspicious, biopsy mandatory
BIRADS VI: known, histologically-verified cancer

Diagnosis is established by combining morphological and functional criteria. A circumscribed round lesion with persistent enhancement is a typical fibroadenoma while the same lesion presenting with washout may be cancer (typical in high risk population, aggressive cancers).

Interpretation points

Clinical history and correlation with mammography is not only diagnostically useful (e.g. to reduce the number of BIRADS III category assignments) but should be considered in the report as well in order to demonstrate to the referring physician that the clinical question has been answered.

Positive predictive value (PPV) of MRI

in high risk screening population: 3 - 4% prevalence when mammography was negative ( 0.3% when mammography and ultrasound negative)
7% if a personal history of cancer
positive predictive value 24% (½ invasive 4 mm median size / ½ DCIS)
- biopsy recommended in 17%

Extent of disease

contralateral breast
- 5% prevalence
- 20% positive predictive value (biopsy recommended in 1/3) (NEJM 29/3/2007: biopsy recommended in 12% PPV 25%);
ipsilateral breast
- ~25%
50% PPV (biopsy recommended in 50%)
ipsilateral multifocal ¾ (same quadrant >1 cm from index CA or contiguous but extends >4 cm) multicentric ¼; distribution similar to recurrent disease
additional sites of ipsilateral cancer more frequent if +FH (42%) & ILC (55%)
positive predictive value higher the closer the lesion is to the index cancer.
biopsy to get histological diagnosis no matter how suspicious because result is mastectomy
younger patients because of 1-2% / year recurrence may also benefit from preoperative MRI
true and false positive rates decrease with each subsequent comparison MRI

MRI sensitivity

IDC/ILC: >90%
DCIS: 80-90%
implant rupture: ~94% ⁹

Indications for breast MRI

ACR guidelines

high risk screening
- personal history
- family history
- high risk lesions: ADH/ALH/LCIS
- BRCA1 / BRCA2 gene positivity
- mantle radiotherapy (>4 gray)
- Li-Fraumeni syndrome +/- first-degree relatives
- Cowden and Bannayan-Riley-Ruvalcaba syndromes and first-degree relatives
extent of disease (EOD) evaluation in ipsilateral and contralateral breast
positive margins (better accuracy further from lumpectomy site than near lumpectomy site due to postoperative changes)
neo-adjuvant chemotherapy: to assess residual disease
metastatic axillary lymphadenopathy of unknown primary (75 - 80% sensitive) - can spare a patient from having management because may be able to undergo BCT; management path only finds cancer in two-thirds
posterior lesion to assess chest wall invasion (pectoralis can be resected so not considered
chest wall stage IIIB - serratus anterior muscle, rib, intercostal muscles)

ACS recommendations

BRCA+ : BRCA1 or BRCA2
1^st degree relative BRCA+ and untested
those who have had prior radiotherapy to chest wall
>25% lifetime risk based on genetic models (some of which take breast density into consideration)
not recommended if lifetime risk <15% because of high false positive rate

Other possible indications

problem solving (e.g. post operative breasts with distortion)
recurrent breast cancer/scar changes (not usual before 2 - 3 years; peak 5 - 7 years; increased risk if EIC, younger age, positive margins (wait at least 1 month postop to scan), no radiotherapy)
to assess for synchronous, multifocal or multicentric disease

MRI features and PPV

Mass

spiculated mass: 80%
irregular shape: 32%
<5 mm mass: 3%

Non-mass

calcifications
- segmental: 67%
- clumped ductal: 31%

Ductal enhancement

malignant causes: DCIS, invasive cancer
benign high risk causes: ADH, LCIS
benign: fibrosis, ductal hyperplasia, fibrocystic change

MRI-detected cancers

40-50% cancers should be <1 cm
at least 20-30% should be DCIS
positive nodes <20%

False negatives

technical causes: breast tissue not included in the coil, motion, bad contrast injection, too much compression
marked background enhancement

An important caveat is that if mammography or ultrasound is positive or there is a palpable finding then there is a need to treat/biopsy/excise despite negative MRI.

Ultrasound correlation

MSKCC: only 23% probably low but if lesion is less than 1 cm or deep within lots of background parenchyma in a large breast may want to go directly to MR guided biopsy