Breast MRI

Breast MRI is a rapidly growing fieldthe most sensitive method for detection of breast cancer. Depending on international health regulations, especially in the assessmentit is either applied for screening of women at high risk womenfor developing breast cancer (e.g. BRCA-1 and BRCA-2 carriers), as an additional diagnostic test in pretherapeutic breast cancer staging, monitoring of primary systemic therapies and for solving problematic diagnostic situations were 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Editorial board note: this article is probably outdated, lacks structure and is in need of a major rewrite.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.

Sequences used

• Dynamic T1-weighted gradient echo before and after IV Gd injection
• T2T2w-TSE or STIR sequences
• T1 C+ (GdDiffusion Weighted Imaging (DWI) : dynamic and kinetic analysis
• ​Further techniques such as e.g. proton MR-spectroscopy seldomly applied outside research settings

Lexicon

• densityAmount of fibroglandular tissue (FGT)
  • Almost entirely fat: ACR a
  • background enhancement
    • none/minimalScattered fibroglandular tissue: <25%ACR b
    • mildHeterogeneous fibroglandular tissue: 25-50%ACR c
    • moderateExtreme amount of fibroglandular tissue: 50-75%
    • marked : >75%ACR d
  • focusBackground Parenchymal Enhancement (BPE)
    • minimal
    • mild
    • moderate
    • marked

  Lesions:

  Usually, enhancing lesions are meant. Absence of enhancement practically excludes breast cancer with an NPV>99%.

  • Focus (formerly defined as < 5 mm): cannot characterizeenhancement too small to be charaterized, should be considered as BPE if symmetric and multiple
  • Mass enhancement (space occupying lesion, best diagnostic clue: margins, etc
  • mass enhancement can be assessed)
    • shape: round (unspecific), oval, lobulated (rather benign), irregular (rather suspicious)
    • marginsMargins: smoothCircumscirbed (benign), irregularNon-circumscribed (rather suspicious), speculated spiculated (highly suspicious)
    • internalInternal enhancement pattern: homogenous (rather benign), heterogenous (unspecific), rim (rather suspicious, in particular if centripetal, filling up over time), dark or enhancement, internal septations (rather benign), old BI-RADS included central (targetenhancement (part of the lesion enhances, highly specific for fibroadenoma)
  • non massNon-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 ductal, linear clumped, segmental patchy/clumped(rather suspicious), regional, diffusemultiple regional, segmental (rather suspicious)
    • Internal enhancement pattern: homogeneous (rather benign), heterogeneous (unspecific), clumped (rather suspicious), clustered ring (rather suspicious, seldomly seen), old BI-RADS included stippled, punctate, bilateral symmetric - it is important to scan both breasts for comparisona homogeneous grainy enhancement typically benign
  • linear enhancement
  • In all lesions: enhancement kinetics: see breast MRI enhancement curves
    • washoutWashout (rather suspicious), plateauPlateau (unspecific), persistent Persistent (rather benign) (caveat: papillomas and lymphLymph nodes washoutshow Washout but typical morphology)
    • ~ 70% of invasive cancers wash out 
    • ~ 9% of DCIS washes out

  MRI BI-RADS Assessment categories

  • BIRADS 0: use very sparingly; confirming lymph node or fibroadenoma on ultrasound or confirmingIncomplete/Non-diagnostic - this category should not be used for marked BPE, motion artifacts etc
  • BIRADS I: Negative (no enhancing lesions, no benign process on mammogram and mammogram not availablechanges such as scars, cysts etc)
  • BIRADS II: lymphBenign (lymph nodes, inflamed cysts, fibroadenoma, fat necrosis, foci/stippled enhancement, background enhancementpatchy BPE).
  • BIRADS IIIAIII: probably benign, requiring short term follow-up (in 1-3in 6 months) no mass likely hormonal enhancement (day 7-14 unless patient has known cancer. If the finding is visible on e.g. US, the most widely available method should be used for EOD eval or 2 - 3 weeks off hormone replacement therapyfollow-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 IIIBIV: 6 month follow-up for mass enhancement after having evaluated for benign morphology and kinetics; probably benign: < 5 mm without rim enhancement, spiculation or washoutsuspicious finding requiring biopsy (Biopsy should always be tried by US first as the majority of MRI lesions can be localized by targeted ultrasound
  • BIRADS IIIA & BV: follow for 2 years (6 monthhighly suspicious, 1 yearbiopsy mandatory
  • BIRADS VI: known, 2 year. (whereas mammogram 3 years; 24% of 1^st time MRI given BI-RADS 3; 0-10%histologically verified cancer rate (3% MSKCC; small invasive cancers and DCIS)

  ItDiagnosis is important to remember that as most MRIs ofestablished by combining morphological and functional criteria. A circumscribed round lesion with persistent enhancement is a typical fibroadenoma while the breast are performed onsame lesion presenting with Washout may be cancer (typical in high risk population, 17% of smooth masses on 1^st MRI were cancer (2/3 DCIS/ 1/3 Invasiveaggressive cancers). 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 alwaysnot only diagnostically useful and can(e.g. to reduce assignmentthe number of BIRADS III category.

  Cancer detection highest assignments) but should be considered in postmenopausal and for extent of disease (EOD) evaluation (22%) and lowestthe report as well in premenopausal women for high risk screening (10%)order to demonstrate 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 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
    • 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 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, 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 biopsy.