Optimization of Reading Room and Image Display
If the mammograms are screen-film studies, the images are viewed on high-intensity viewboxes with the light parts of the films masked to block extraneous light. For full-field digital mam- mograms (FFDMs) and tomosynthesis images viewed on soft copy, the images are displayed on high-resolution bright moni- tors in a dark room with little to no ambient light, comparing old studies with new ones in the display protocol. Additionally, an ergonomic setup for the radiologist as described in our article on repetitive stress injury in breast radiologists will help the radiolo- gist avoid injury (Thompson et al., 2014).
First Look at Two-Dimensional Views and Older Studies
The standard set of mammograms consists of paired MLO views and paired CC views. Normal breast tissue is usually symmetric, or “mirror image.” To evaluate for mammographic symmetry, the MLO and CC views are displayed back to back, and asymmetries A
MLO CC
B
FIG. 2.7 The fifth edition of BI-RADS no longer indicates the ranges of percentage dense tissue of the four density categories. In this case, the breast density is classified as heterogeneously dense based on BI-RADS 2013 because the fibroglandular tissue could mask small cancers, even though far less than 50% of volume of the breast con- tains fibroglandular-density tissue. Mediolateral oblique (MLO) view (A) and craniocaudal (CC) view (B).
TABLE 2.1 Mammographic Findings of Breast Cancer Finding Differential Diagnosis
Pleomorphic
calcifications Cancer (most common), benign disease, fat necrosis
Spiculated mass Cancer, postsurgical scar, radial scar, fat necrosis
Mass with calcifications Cancer, fibroadenoma, papilloma;
exclude calcifying oil cyst
Round mass Cyst, fibroadenoma, cancer, papilloma, metastasis
Architectural distortion Postsurgical scarring, cancer
A focal asymmetry Normal asymmetric tissue (3%), cancer (suspicious: new, palpable, a mass containing suspicious calcifications or spiculation)
Developing asymmetry Cancer, hormone effect, focal fibrosis Breast edema Unilateral: mastitis, postradiation therapy,
inflammatory cancer
Bilateral: systemic disease (liver disease, renal failure, and congestive heart failure)
Lymphadenopathy Unilateral: mastitis, cancer
Bilateral: systemic disease (collagen vascular disease, lymphoma, leukemia, infection, and adenocarcinoma of unknown primary)
Single dilated duct Normal variant, papilloma, cancer Nothing 10% of all cancers are false-negative on
mammography
BOX 2.5 Steps in Radiologists Recognizing Cancer on Mammograms
Radiologist sees the finding
Radiologist recognizes the finding is different from normal tissue Radiologist correctly interprets the finding as abnormal/possibly
abnormal
Radiologist acts on the finding (recall/biopsy)
are easily identified using the comparison of the right and left breasts (Fig. 2.8). Look at the whitest part of the mammograms for normal fibroglandular symmetry to see if there is more white tissue on one side than on the other (an asymmetry) or if there are any abnormal spots focally whiter than background (a focal asymmetry).
Asymmetries can be normal. For example, normal asymmetric glandular tissue is defined as a larger volume of normal fibroglan- dular tissue in one breast than the other, but with one breast not necessarily being larger than the other; this occurs in about 3% of women. A normal asymmetry should be stable over time.
To detect changes over time, good quality older mammograms are placed above the new ones. Because subtle changes may take longer than a year to become evident, one compares new mam- mograms with last year’s mammogram, one more than 2 years old, and the oldest images of comparable quality.
Unexplained increases in breast density may indicate breast cancer. An unexplained generalized increase in breast density associated with skin thickening may represent breast edema, which has many etiologies, including inflammatory cancer. An unexplained new asymmetric focal density is called a “develop- ing asymmetry” and should prompt investigation because devel- oping asymmetries represent cancer in 15% of cases.
Comparing old studies with current studies makes it easier to see new or developing changes. A normal mammogram does not usually change from year to year after taking into account the normal involution of glandular tissue (Fig. 2.9). Contrastingly, malignant lesions increase in size and can change the mammo- graphic appearance over time. However, the changes on mam- mography caused by tumors can be very subtle. Some tumors may infiltrate into the breast tissue without producing an appar- ent contrast against fat (Fig. 2.10). The doubling time of breast
RCC LCC
LCC RCC
RMLO LMLO
RMLO LMLO
OLD
NEW
FIG. 2.8 Schematic of viewing normal mammograms to judge the symmetry and change over time. The mediolateral oblique (MLO) and craniocaudal (CC) mammograms are viewed with the right and left sides placed back to back. Older mammograms are placed above to check for change from year to year. R, right; L, left.
A
Old MLO Old CC
New MLO New CC
B
FIG. 2.9 Example of normal stable mammograms in viewing scheme. (A) Normal old mediolateral oblique (MLO) and craniocaudal (CC) views are placed back to back above the new views. (B) Normal new MLO and CC views, also placed back to back. Comparing the new and old studies shows no change in dense tissue and a stable benign nodule (arrow in A and B) in the medial left CC view over a 4-year period.
Old MLO Old CC
A
New MLO New CC
B
C D
FIG. 2.10 Developing asymmetry over 3 years. (A) Normal old mediolateral oblique (MLO) and craniocaudal (CC) views are placed back to back above the new views. (B) New MLO and CC views, also placed back to back, showing developing asymmetry (arrows) in the medial upper left breast. Although the asymmetry looks subtle, comparison of the new study with the older study performed 3 years before (A) helps to identify this abnormality. (C) Ultrasonography shows two masses in the 11:00 to 11:30 position. (D) A sagittal plane of contrast enhanced magnetic resonance imaging shows masses and nonmass enhancement involving the nipple in the upper left breast.
This patient was proven to have invasive ductal cancer.
cancer is typically approximately 50 to 200 days, but some can grow more slowly (Fig. 2.11).
Systematic Search on Each Mammographic Two-Dimensional View and Tomosynthesis
Once the radiologist judges the mammographic density and asymmetries, they search for masses, calcifications, and distor- tions on the mammograms. A common search pattern uses zig- zags or strips of each image, like mowing a lawn with a lawn- mower or searching for a lost boat at sea with a rescue helicopter.
For two-dimensional (2D) digital mammography, the radiologist electronically magnifies the mammograms in quartiles, the upper half and the lower half of the 2D MLO views and the inner and outer 2D CC views (Fig. 2.12).
On tomosynthesis, the radiologist first reviews the 2D or syn- thesized 2D mammogram initially using the zigzag/strip method, then proceeds to magnify the 2D/synthesized 2D mammogram in quartiles because it is harder to see the overall breast in tomosynthesis slices or slabs alone. Then the radiologist scrolls through tomosynthesis slices or slabs. Some radiologists syn- chronize the tomosynthesis slabs or slices together, back to back, similar to the 2D display, to look for symmetry and auto scroll the tomosynthesis as a movie to get an overall view of the breast. For detailed tomosynthesis analysis, similar to reading a computed tomography (CT) scan or magnetic resonance imaging (MRI), it is important for the radiologist to keep his or her eyes in one place as the movie is scrolled/played to analyze a specific area.
Otherwise, the eye is moving and the images are moving, and a finding could be missed. For example, the radiologist scrolls through all the tomosynthesis slices/slabs keeping his or her eye on the upper right breast MLO throughout the series, the lower right MLO, the upper left MLO, and then the lower left MLO. The radiologist then repeats the procedure for the CC studies. The method to review the tomosynthesis is described in Fig. 2.13.
If the radiologist is reviewing the tomosynthesis on slabs, and there is a suspicious finding seen on a slab, then the findings are reviewed on the tomosynthesis slices.