Breast MRI

Breast MRI is a rapidly growing field, especially in the assessment of high risk women. 

Editorial board note: this article is probably outdated, lacks structure and is in need of a major re writerewrite.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

Sequences used

• T1
• T2
• T1 C+ (Gd) : dynamic and kinetic analyisisanalysis

Lexicon

• density
• background enhancement :
  • none / minimal /minimal: < 25;25%
  • mild: 25 - 50-50%
  • moderate: 50 - 75-75%
  • marked : > 75;75%
• focus < 5 mm: cannot characterize margins, etc.
• mass enhancement :
  • shape: round, oval, lobulated, irregular
  • margins: smooth, irregular, speculated
  • internal: homogenous, heterogenous, rim, dark or enhancement, internal septations, central(target)
• non mass enhancement :
  • focal, linear ductal, linear clumped, segmental patchy/clumped, regional, diffuse
  • stippled, punctuatepunctate, bilateral symmetric. It - it is important to scan both breasts for comparison.
• linear enhancement :
• enhancement kinetics: see >> breast MRI enhancement curves
  • washout, plateau, persistent (caveat: papillomas and lymph nodes washout)
  • ~ 70% of invasive cancers wash out 
  • ~ 9% of DCIS washes out

Assessment categories

• BIRADS 0: use very sparingly; confirming lymph node or fibroadenoma on ultrasound or confirming benign process on mammogram and mammogram not available
• BIRADS II: lymph nodes, inflamed cysts, fibroadenoma, fat necrosis, foci/stippled enhancement, background enhancement.
• BIRADS IIIA: short term follow-up (in ~ 1 - 3-3 months) no mass likely hormonal enhancement (day 7-14 unless patient has known cancer for EOD eval or 2 - 3 weeks off hormone replacement therapy.)
• BIRADS IIIB: 6 mo. f/umonth follow-up for mass enhancement after having evaluated for benign morphology and kinetics -Prob. Benign; probably benign: < 5 mm w/owithout rim enhancement, spiculation or washout
• BIRADS IIIA & B: follow for 2 years (6 moonthmonth, 1 year, 2 year.) (whereas mammomammogram 3 years; 24% of 1^st time MRI given BI-RADS 3; 0-10% cancer rate (3% MSKCC; small invasive cancers and DCIS)

It is important to remember that as most MRIs of the breast are performed on high risk population, 17% of smooth masses on 1^st MRI were cancer (2/3 DCIS/ 1/3 Invasive). Thus one must not apply the same rules as to ultrasound on low risk patient; i.e. if washes out the lesion needs to be biopsied. 

Similarly ductal enhancement should always prompt a biopsy.

Interpretation points

Clinical history and correlation with mammography is always useful and can reduce assignment of BIRADS III category.

Cancer detection highest in postmenopausal and for extent of disease (EOD) evaluation (22%) and lowest in premenopausal women for high risk screening (10%)

Positive predictive value (PPV) of MRI

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

Extent of disease (EOD)

• contralateral breast :
  • 5% prevalence prevalence
  • 20 % positive predictive value (biopsy recommended in 1/3) (NEJM 3/29/07: Bx rec in 12 % PPV 25 %);
• Ipsilateral breast :
  • ~ 25%
  • 50% PPV (biopsy recommended in 50%)

Ipsilateral multifocal ¾ (same quadrant > 1cm 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 Mx

Younger patients because of 1 - 2% / year recurrence may also benefit from preop MRI

True and false positive rate decreases 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 Lx site b/c postop enh/changes)
• neo-adjuvant chemotherapy : to assess residual disease
• metastatic axillary lymphadenopathy of unknown primary (75 - 80% sensitive) - can spare a patient from having Mx b/cmanagement because may be able to undergo BCT; Mxmanagement path only finds cancer in 2/3two-thirds
• posterior lesion to assess chest wall invasion (pectoralis can be resected so not considered
• chest wall stage IIIB- serratus anterior, rib, intercostal muscles)

ACS recommendations

• BRCA+ : BRCA 1 or BRCA 2
• 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 post op to scan), no RT)
• 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

Caveat : if mammography or ultrasound is positive or palpable finding 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 biospybiopsy.