Introduction to Breast Imaging

Overview

Breast Anatomy
Breast Cancer Epidemiology and Risk Factors
MQSA and Technical Considerations
Screening Mammography
Diagnostic Mammography
Report Organization
Definitions of Terms

A good understanding of the basic breast anatomy is essential in the detection of cancers.

Gross Breast Anatomy

Skin, nipple, and areola
Subcutaneous and retromammary fat
Pre-mammary fascia
Separates subcutaneous fat from glandular cone
Glandular cone
This is our primary focus in breast imaging since it is where breast cancer occurs
Retromammary fascia
Separates retromammary fat from glandular cone
Vascular and lymphatic vessels
Pectoralis muscles and ribs

Figure 1. Normal Breast Anatomy, see specific labels showing the suspensory ligaments (Cooper’s), lobes, and lactiferous ducts.

Breast Anatomy: Components of the Glandular Cone

The lactiferous/mammary ducts extend in a fan-shaped fashion from the nipple, running within the lobes
There are typically 15-25 lobes (each of which consist of numerous lobules) forming a distinct compound alveolar gland opening at the nipple
individual ducts coalesce near the nipple to form the terminal ducts.
Cooper’s (suspensory) ligaments extend from the fascia and separate the lobes, supporting the breast and giving it shape
Terminal ductal lobular unit (TDLU)
Short segment of a terminal duct and cluster of ductules and acini, resembling a cluster of grapes (see Fig 1, and Fig 2)
Functional unit of the breast, as well as where ductal and lobular carcinomas form

Figure 2. Histology Slide showing the normal Terminal Ductal Lobular Unit (TDLU).

Breast Cancer Epidemiology

Most frequently diagnosed malignancy (excluding skin cancers)
26% of all cancers detected
American women have a 1-in-8 lifetime risk of developing breast cancer
2nd leading cause of cancer mortality in women (15% of all cancer deaths) only lung cancer kills more women each year.
Breast cancer death rates have been decreasing steadily since 1989 for an overall decline of 43% through 2020
- Thought to be related to both improved treatment as well as earlier breast cancer detection (primarily via screening mammography)

Risk Factors for Breast Cancer

The number one risk for breast cancer is having breasts.
Age – The incidence of breast cancer increases with age
Personal or family history of breast cancer
Genetic mutations such as BRCA1 and BRCA2
These make up only 5-10% of breast cancers in the USA
Earlier age of onset
Multiple primaries, often bilateral
BRCA1: 85% lifetime risk; 40-50% risk of ovarian cancer by age 70
BRCA2: 85% lifetime risk, but at a later age of onset; 27% risk of ovarian cancer by age 70
Prolonged exposure to unopposed estrogens
Early menarche or late menopause
Nulliparity or late first-term pregnancy
Postmenopausal obesity or hormone replacement therapy
Chest wall exposure to high-dose radiation, usually for Hodgkin's lymphoma. This is age-dependent. Women exposed prior to age 40 have significant increases in risk. However, women exposed after the age of 40 have a very small risk.
Biopsy showing:
- Sclerosing adenosis (1.5-2x)
- Ductal papilloma (1.5-2x)
- Radial scar (~1.8x)
- Proliferative changes without atypia (1.5-2x)
- Proliferative changes with atypia (4-5x)
- Atypical ductal hyperplasia (ADH; 4-5x)
- Atypical lobular hyperplasia (ALH; 4-5x)
- Lobular carcinoma in situ (LCIS; 8-10x)
- Re-excision is recommended for any biopsy with atypia, radial scar, LCIS, and papillomas with atypia or incompletely excised papillomas

Prognostic Factors

Status of axillary lymph nodes on histologic evaluation (from lymph node dissection or sentinel lymph node biopsy) is the most important prognostic factor
Tumor size <1 cm correlates with an average 20-year survival rate of 87%
Estrogen receptor (ER) and progesterone receptor (PR) positivity affect therapy options and are a good prognostic indicator
Human epidermal growth factor receptor 2 (HER2/neu) over-expression is a poor prognostic indicator and should prompt treatment with HER2-targeted agents, which significantly positively affect survival rates. Currently, survival rates exceed 90% in HER2-positive breast cancer patients who are diagnosed early and treated with chemotherapy and dual antibody therapy
p53 tumor suppressor gene mutation has a poorer prognosis (tends to be aneuploid, ER-negative, high-grade tumors)

MQSA, QC, and Technical Considerations

Mammography Quality Standards Act (MQSA; 1992)

Response to many nationwide problems in mammography, including:
Poor quality equipment
Poorly trained technologists and physicians
Lack of quality assurance procedures
Annual inspections; accreditation every 3 years
Physician must be:
Board certified (or have 3 months of formal training in mammography)
Complete 60 hours of Category I CME credits in mammography, with at least 15 in the 3 years prior
240 mammograms interpreted under supervision in 6 months prior
To maintain qualification:
960 mammograms interpreted per 24 months
15 category I CME credits in 36 months
All reports must contain a final assessment with recommendations
All mammographic study results and recommendations must be conveyed to patients in writing using lay language

Technical Evaluation of Images

CC:
- Distance from nipple to the posterior edge of the film should be within 1 cm of PNL (posterior nipple line) length on MLO
MLO:
- The pectoral muscle should have a convex border and should extend inferiorly to the level of the nipple
- Motion blurring:
Most likely to occur in the inferior breast on MLO
Usually related to poor compression and long exposure times
Negatively impacts the ability to detect microcalcifications
A small portion of the upper abdomen should be seen to ensure the inframammary fold is included Artifacts to be aware of:
- Deodorant, body powder, and lotions can simulate breast calcifications)
- Tattoos (can present as calcifications consolidating in axillary lymph nodes)
- Body part projecting on image (chin, ear lobe, arm, etc.)

Digital Mammography/Tomosynthesis (DBT)

Benefits
Decreased image acquisition times when using two-dimensional digital mammography.
Significant increases in acquisition time for tomosynthesis.
Increased imaging contrast and wider display latitude, with the ability to manipulate after exposure
Decreased detector noise
Tele-mammography
Computer-aided detection (CAD) facilitated
Tomosynthesis is a game changer in the mammography world, allowing for increased cancer detection rate and decreased callback rate
Drawbacks
Decreased spatial resolution (5-10 lp/mm compared with 20 lp/mm for film-screen)
Expensive initial cost
Significant storage space is required to retain images, particularly for tomosynthesis

Computer-Aided Detection (CAD)

Images are analyzed by a computer software program prior to physician interpretation
Marks are made to direct attention to possible masses and suspicious calcifications
Interpreting radiologists should use CAD only as a guide for detecting findings
Can be used on analog films, but they must be digitized first
Reported 20% increase in cancer detection
Sensitivity for calcifications is higher than for masses

Screening Mammography

Exam performed on an asymptomatic woman to detect early, clinically unsuspected breast cancer
A major role of mammography is the early detection of breast cancer in asymptomatic women
Clinical trials have shown absolute mortality reduction due to the ability to find DCIS and infiltrating cancers of a smaller size and earlier stage than in unscreened control groups
Yearly screening is recommended beginning at age 40 according to the American College of Radiology Guidelines.
Standard views include bilateral craniocaudal (CC) and medial-lateral oblique (MLO)
Compression for the MLO view is oriented along the axis of the pectoralis muscle; the beam enters from the upper-inner quadrant and exits the lower-outer quadrant
Exaggerated CC (XCCL) views can also be performed to include axillary tail tissue
Both implant and implant-displaced (ID) views in the CC and MLO projections are included in the appropriate setting

ACR Screening Mammography Recommendations

“Asymptomatic women 40 years and older* have annual mammographic screening.”
“Mammographic screening before the age of 40 may benefit women who are at high risk for breast cancer.”
In general, patients with a first-degree relative with breast cancer begin screening 10 years before a relative was diagnosed but not before the age of 25

Figure 3. Screening Mammogram

Diagnostic Mammography

Patients who have clinical signs/symptoms suggesting breast cancer or positive findings on screening mammography are recalled for further evaluation with additional views.
In addition to standard views, diagnostic views include:
True 90° medial-lateral (ML) or lateral-medial (LM) views
Cleavage view (CL) or axillary tail view (AX)
Rolled views (RLCC or RMCC; RSML or RIML)
Tangential view (TAN)
Spot compression views
Spot magnification views

Figure 4. Cleavage View for Diagnostic Mammogram

Figure 5. Tangential View: this view is performed for palpable abnormalities. A BB marker is placed on the skin over the area of clinical concern. The technologist then obtains an image with the BB in tangent.

Figure 6. Spot Compression RCC diagnostic mammogram.

Figure 7. Spot Magnification LCC diagnostic mammogram, the area of concern, is magnified and used primarily to evaluate calcifications.

Diagnostic Mammography (continued)

NEVER forget to evaluate the rest of the breast, as well as the contralateral breast
Physician reading a diagnostic mammogram is responsible for findings missed on the associated screening mammogram, even if someone else reported it

Work-up of Palpable Abnormalities

Women < 30:
Work-up begins with an ultrasound
A mammogram is only done in the setting of a suspicious underlying ultrasonographic abnormality
Women > 30:
Work-up begins with a mammogram, but an ultrasound is done regardless of the findings
Palpable abnormalities without mammographic findings require further evaluation with ultrasound
Ensure that clinical (palpable), mammographic, and ultrasonographic findings all correlate in location
While Negative imaging should be given a BIRADS 2 designation, further clinical management of a palpable abnormality should be recommended. Negative imaging should never deter further workup.
Negative imaging should be given a BIRADS 2 designation. However, further clinical management of a palpable abnormality should be recommended. Negative imaging should never deter further workup.

Report Organization

Indication for exam
Screening exam with no complaints
Recall for finding on prior screening
Clinical abnormality
Follow-up of BIRADS 3 lesion or conservatively treated breast cancer
Technique
Views obtained
Comparison to previous studies
Findings
Statement of breast composition
Positive findings
Pertinent negatives
Impression (including Assessment Category)

Breast Composition

Assessment of the volume of normal attenuating breast tissue
Gives an indication of the overall sensitivity of the exam
4 patterns

Figure 8. The breast is almost entirely fat.

</25% glandular tissue
High sensitivity for screening

Figure 9. There are scattered fibro glandular densities.

~25-50% glandular
Slightly decreased sensitivity

Figure 10. The breast tissue is heterogeneously dense.

~51-75% glandular
“This may obscure the detection of small masses.”

Figure 11. The breast tissue is extremely dense

>75% glandular
“This may lower the sensitivity of mammography.”

Changes in Breast Composition

Breast parenchyma normally decreases gradually in density with age
Increased estrogen and progesterone during pregnancy can cause bilateral diffuse increase in breast density
25% of patients on hormone replacement therapy (HRT) can demonstrate a similar increase in breast density

Breast Imaging Reporting and Data System (BI-RADS) Assessment Categories

0: Incomplete assessment
Additional imaging and/or prior exams required
1: Negative
Recommend annual screening
2: Benign finding(s)
Recommend annual screening
3: Probably benign finding(s)
Initial short-term follow-up recommended

BI-RADS 3

Findings should have a <2% risk of malignancy
BI-RADS 3 should never be given on a screening examination
BI-RADS 3 should not be given for a palpable lesion
On follow-up examinations, a change in size of greater than 20% or significant changes in character or margin should prompt an immediate biopsy recommendation

BI-RADS 3 Follow-Up Timeline

Time 0: Initial screening exam (BI-RADS 3)
At 6 months: unilateral exam (BI-RADS 3)
At 12 months: bilateral exam (BI-RADS 3)
At 24 months: bilateral exam (BI-RADS 2)
*This schedule assumes that there is no change in the lesion over the course of the follow-up
**An initial 3-month follow-up can be performed in patients with questionable post-operative changes or an inflammatory condition in which rapid changes are expected

BI-RADS Assessment Categories (continued)

4: Suspicious abnormality
Biopsy should be considered
~2-94% chance of malignancy
5: Highly suggestive of malignancy
Appropriate action should be taken (may include percutaneous biopsy vs. one-stage surgical treatment)
>95% chance of malignancy
6: Biopsy-proven malignancy
Second opinions
Follow-up after neoadjuvant chemotherapy

BI-RADS Assessment Categories (continued)

A single assessment category is given for the entire report based on the most worrisome findings
Screening mammograms should only have a BI-RADS assessment category of 0, 1, or 2
All BI-RADS 0 should include a recommendation for the next course of action
All BI-RADS 4 or 5 should be associated with a recommendation for biopsy, including a suggestion for appropriate guidance technique
These findings should be discussed with both the patient and the referring clinician, and that discussion should be documented in the report
Patients with a palpable abnormality but no imaging findings should be given a BI-RADS 1 or 2 assessment, with an additional note that follow-up should be based on clinical exam

Terms You Should Know

Multifocal disease: tumor foci within the same quadrant of the breast
Can be treated with lumpectomy
Multicentric disease: tumor foci in different quadrants of the breast
Lumpectomy contraindicated
Synchronous cancer: bilateral cancers detected simultaneously
5-10% of all cancers are shown by MRI to be bilateral at the time of diagnosis
Incidence increases to 30% if pathology indicates ILC
Metachronous cancer: bilateral cancers detected at different points in time
Risk of developing subsequent lesion after initial breast cancer diagnosis is ~1% per year
Concordance: biopsy result confirms imaging suspicions
Discordance: biopsy result does not agree with imaging findings
For example, benign pathology in the setting of a BIRADS 5 / highly suspicious lesion on imaging)
Consider recommending excisional biopsy in this situation

Introduction to Breast Imaging

Chapter 1