Breast MRI

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[edit] Lexicon

  • Density
  • Background enhancement:
    • None/Minimal < 25%
    • Mild 25-50%
    • Moderate 50-75%
    • Marked >75%
  • Focus < 5mm; cannot characterize margins, etc.
  • Mass enhancement:
    • Shape: Round, oval, lobulated, irregular
    • Margins: Smooth, irregular, speculated
    • Internal: Homo, hetero, rim, dark or enh. internal septations, central(target)
  • Non mass enhancement:
    • Focal, Linear ductal, linear clumped, segmental patchy/clumped, regional, diffuse
    • Stippled, punctuate, bilateral symmetric (always scan both breasts!!)
  • Enhancement kinetics:
    • washout, plateau, persistent (caveat: papillomas and LNs washout)
    • 70% invasive cancers wash out; 9% DCIS washes out

[edit] Assessment Categories

  • BI-RADS 0: use very sparingly; confirming LN or FA on US or confirming benign process on mammo and mammo not available
  • BI-RADS 2: LN, inflamed cysts, FA, fat necrosis, foci/stippled enh., background enh.
  • BI-RADS 3A: short term f/u (1-3 mo.) nonmass likely hormonal enh (day 7-14 unless pt. has known CA for EOD eval or 2-3 weeks off HRT
  • BI-RADS 3B: 6 mo. f/u for mass enhancement after having evaluated for benign morphology and kinetics -Prob. Benign: < 5 mm w/o rim enhancement, spiculation or washout
  • BI-RADS 3A&B: follow for 2 years (6 mo, 1 yr, 2 yr.) (whereas mammo 3 years; 24% of 1st time MRI given BI-RADS 3; 0-10% cancer rate (3% MSKCC; small invasive cancers and DCIS)
  • 17% of smooth masses on 1st MRI were cancer (2/3 DCIS/ 1/3 Invasive) b/c high risk pop. So different from US benign features; if washes out Bx
  • Ductal enhancement – always biopsy

[edit] Interpretation points

  • Clinical History and correlation with mammo when appropriate
  • IMPORTANT; can reduce assignment of BIRADS 3 category
  • Cancer detection highest in postmenopausal and for EOD evaluation (22%) and lowest in premenopausal women for high risk screening (10%)

[edit] PPV of MRI

  • High Risk Screening Population: 3-4% prevalence when mammo was neg. (mammo and US 0.3%)
  • 7% if personal history of CA
  • PPV 24% ( ½ invasive 4 mm median size/ ½ DCIS) Bx recommended in 17%

[edit] EOD

  • C/L Breast: 5% prevalence; 20% PPV (Bx recommended in 1/3) (NEJM 3/29/07: Bx rec in 12% PPV 25%);
  • I/L Breast: ~25%; 50% PPV (Bx recommended in 50%)
  • I/L multifocal ¾ (same quadrant > 1cm from index CA or contiguous but extends > 4 cm) multicentric ¼; distribution similar to recurrent disease
  • Additional sites of I/L cancer more frequent if +FH (42%) & ILC (55%)
  • PPV higher the closer the lesion is to the index cancer
  • Bx to get histological diagnosis no matter how suspicious b/c result is Mx
  • Younger patients b/c of 1-2%/yr recurrence may also benefit from preop MRI
  • True and False positive rate decreases with each subsequent comparison MRI

[edit] MRI sensitivity

  • IDC/ILC >90%
  • DCIS 80-90%

[edit] Indications

[edit] ACR guidelines

  • High Risk Screening: personal history, family history, high risk lesions (ADH/ALH/LCIS), BRCA1/BRCA2, Mantle RT (>4 Gray)
  • EOD evaluation in I/L and C/L breast
  • Positive margins (better accuracy further from Lx site than near Lx site b/c postop enh/changes)
  • Neoadjuvant chemotherapy
  • Metastatic axillary lymphadenopathy of unknown primary (75-80% sensitive)- can spare a patient from having Mx b/c may be able to undergo BCT; Mx path only finds cancer in 2/3
  • Posterior lesion to assess chest wall invasion (pectoralis can be resected so not considered
  • Chest wall stage IIIB- serratus anterior, rib, intercostal muscles)

[edit] ACS recommendations

  • BRCA+
  • 1st degree relative BRCA+ and untested
  • RT
  • > 25% lifetime risk based on genetic models (some of which take breast density into consideration)
  • Not recommended if lifetime risk<15% b/c of high FP rate

[edit] Other possible indications

  • Problem solving (e.g. post op breasts with distortion)
  • Recurrent breast cancer/ scar changes (not usual before 2-3 yrs; peak 5-7 years; increased risk if EIC, younger age, positive margins (wait at least 1 month post op to scan), no RT)

[edit] MRI features and PPV

  • Mass
    • Spiculated mass 80%
    • Irregular shape 32%
  • Non mass
    • Segmental 67%
    • Clumped ductal 31%
    • < 5 mm mass 3%

[edit] Ductal enhancement

  • Malignant causes: DCIS, Invasive CA
  • Benign high risk causes: ADH, LCIS
  • Benign: Fibrosis, Ductal hyperplasia, fibrocystic change

[edit] MRI detected cancers

  • 40-50% cancers should be < 1 cm
  • At least 20-30% should be DCIS
  • Positive nodes < 20%

[edit] False negatives

  • Technical causes: Breast tissue not included in the coil, motion, bad contrast injection, too much compression
  • Marked background enhancement
  • Caveat: if mammo or US is positive or palpable finding need to treat/biopsy/excise despite negative MRI!

[edit] US 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 Bx

[edit] References

  • MSKCC Breast Cancer Conference 2006