◊  >90% of nipples contain 5–9 ductal orifices

(b)  multiple other blind-ending orifices: connected to sebaceous glands of 1–4 cm in length

√  bilateral symmetric enhancement pattern of normal nipple:

√  1–2 mm superficial layer of intense linear enhancement

√  underlying region of nonenhancement deep to dermis

Ducts

lactiferous ducts coalesce in subareolar region into 5–8 mm wide lactiferous sinuses exiting in the central portion of nipple; organized into

(a)  central ducts: extending to chest wall

(b)  peripheral ducts: arranged in a radial fashion

Main lactiferous duct → branches dichotomously into segmental duct → subsegmental duct → terminal duct → blunt-ending acinus

Terminal Duct Lobular Unit (TDLU)

(1)  Extralobular terminal duct

Histo:   lined by columnar cells + prominent coat of elastic fibers + outer layer of myoepithelium

(2)  Lobule

(a)  intralobular terminal duct

Histo:   lined by 2 layers of cuboidal cells + outer layer of myoepithelium (for milk propulsion)

Significance:   invasive ductal, papillary, mucinous, medullary adenoid cystic cancers arise from ductal epithelium in TDLU and most commonly appear as spiculated irregular masses ± calcifications / developing asymmetries

(b)  ductules / acini

(c)  intralobular connective tissue

Size:     1–2 (range, 1–8) mm in diameter

Change:

(a)  reproductive age: cyclic proliferation (up to time of ovulation) + cyclic involution (during menstruation)

(b)  post menopause: regression with fatty replacement

Significance:

TDLU is the site of fibroadenoma, epithelial cyst, apocrine metaplasia, adenosis (= proliferation of ductules + lobules), epitheliosis (= proliferation of mammary epithelial cells within preexisting ducts + lobules), ductal + lobular carcinoma in situ, infiltrating ductal + lobular carcinoma

Components of Normal Breast Parenchyma

1.   Nodular densities surrounded by fat

(a)  1–2 mm = normal lobules

(b)  3–9 mm = adenosis

2.   Linear densities

=  ducts and their branches + surrounding elastic tissue

3.   Structureless ground-glass density

=  stroma / fibrosis with concave contours

Parenchymal Breast Pattern (László Tabár)

Effect of breast density on sensitivity:

women in their 40s have a 68% higher risk of a FN screening mammogram compared to older women

Recommendation:   perform mammography during 1^st week of menstrual cycle

Inter- and intraobserver variability on breast density:

›  low reliability of interreader density agreement (κ = 0.59)

›  imperfect intrareader agreement (κ = 0.72)

Factors affecting breast density between mammograms:

body mass index, weight changes, age, HRT, dietary intake

Overall odds ratio of breast cancer for > 75% tissue density:

›  compared to 10% density 4.74

›  with interval cancer developed in 1 year 17.81

Relative risk of cancer associated with breast density:

›  breast tissue density of 50–74% 2.92

›  breast tissue density of > 75% 4.64

Pattern I

named QDY = quasi dysplasia (for Wolfe classification)

√  concave contour from Cooper’s ligaments

√  evenly scattered 1–2 mm nodular densities (= normal terminal ductal lobular units)

√  oval-shaped / circular lucent areas (= fatty replacement)

Pattern II

similar to N1 (Wolfe)

√  total fatty replacement

√  NO nodular densities

Pattern III

similar to P1 (Wolfe)

√  normal parenchyma occupying < 25% of breast volume in retroareolar location

Pattern IV = adenosis pattern

similar to P2 (Wolfe)

Cause:    hypertrophy + hyperplasia of acini within lobules

Histo:  small ovoid proliferating cells with rare mitoses

√  scattered 3–7 mm nodular densities (= enlarged terminal ductal lobular units) = adenosis

√  thick linear densities (= periductal elastic tissue proliferation with fibrosis) = fibroadenosis

√  no change with increasing age (genetically determined)

Pattern V

similar to DY (Wolfe)

√  uniformly dense parenchyma with smooth contour (= extensive fibrosis)

Enhancement of Normal Parenchyma on MR

=  Background Parenchymal Enhancement (BPE)

◊  Breast enhancement does NOT correlate with breast density

•  varies among women + within same woman over time

Proper enhancement present if:

›  veins contrasted on MIP

›  both internal mammary arteries depicted

›  nipple enhances

Common pattern of enhancement:

√  bilateral symmetric diffuse enhancement:

√  slow minimal / early enhancement

√  persistent delayed enhancement

√  linear patchy enhancement

√  confluent enhancement on late dynamic scan

Distribution of enhancement:

√  bilateral symmetric enhancement with

(a)  moderate / marked degree of BPE

(b)  diffuse / regional distribution

(c)  homogeneous / internally stippled

√  “picture framing” of vascular inflow = enhancement commonly begins in periphery + gradually becomes apparent in more central breast tissue

√  scattered innumerable 9–10 mm foci of enhancement

√  geographic areas of symmetric regional enhancement

√  multiple larger symmetric areas of enhancement (DDx: asymmetry suggest malignancy)

BPE Effect on Interpretation of MR Images:

1.   Falsely positive ← focal / regional / asymmetric background parenchymal enhancement

2.   Falsely negative ← moderate / marked BPE

Classification of Background Parenchymal Enhancement:

Hormonal Influence on BPE

1.   Menstruation

√  enhancement high during days 21–28 and days 1–6 after menstruation + low during days 7–20

2.   Lactation

◊  Breast involution after lactation takes 3 months

Note:  NO impairment in cancer detection in lactating patients!

Breast-feeding:   safe after contrast-enhanced MRI ← minute amounts of Gd in breast milk

3.   Postmenopausal period without HRT

√  decrease in fibroglandular tissue → degree of BPE typically less than that in premenopausal women

4.   Hormone replacement therapy (HRT)

√  increase in BPE in amount + degree + distribution with great interindividual variations:

◊  Hormonal effect reverses after 30–60 days

5.   Endocrine antihormonal therapy

Antiestrogenic agents:   selective estrogen receptor modulators, aromatase inhibitors

√  significant decrease in amount of fibroglandular tissue + cysts + BPE

√  effect on BPE evident early in treatment (< 90 days)

√  tamoxifen rebound after medication discontinued:

√  global / focal increase in BPE

6.   Oophorectomy → decrease in BPE

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