MAMMOGRAPHY INTERPRETATION Before Reading Mammogram
Step 1. Overall Search: Quality of Images and Balance of Breast Tissue Density
The first step is the overall search of the whole set of mammo- grams, including bilateral MLO views, bilateral CC views, and additional views if available. Initially, the radiologist looks at the mammographic technique for good quality and then evaluates the balance of the breast tissue density between the breasts and within a breast, ie, the symmetry of breast density and the white parts, respectively.
Checking symmetry between the breasts is essential to detect an abnormal finding on mammography. The normal breast tissue is usually symmetric between the breasts, and an abnormal lesion can produce an asymmetry. However, the nor- mal breast tissue sometimes is asymmetric, meaning that there is more normal glandular tissue in one breast than the other; this is a normal variant, like having one foot bigger than the other.
Normal asymmetry consists of a normal asymmetric volume of breast tissue with more in one side than the other. On the CC and MLO views, the glandular asymmetry should “spread out”
and not look like a mass (Fig. 2.22). Normal asymmetry can also be caused by removal of fibroglandular tissue from one breast by biopsy, making the other breast look like it has more tissue.
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B
Lateral
CC MLO
FIG. 2.18 Triangulation of an outer lower breast mass. (A) Three standard mammographic views are placed with the mediolateral oblique (MLO) view at the middle. An imaginary line (dashed line) connecting an outer lower mass can be drawn in a linear fashion. When drawn though the craniocaudal (CC; left) and MLO views, the imaginary line (dashed line) points at an even lower position of the breast on the lateral view (right). Note that even though the mass is at nipple level on the MLO view, its actual location on the lateral view is at the 5 o’clock position and not the 3 o’clock position. Triangulation is helpful for predicting the lateral position from CC and MLO. (B) Ultrasound shows a round microlobulated mass at the 5 o’clock position of the left breast that was diagnosed as invasive ductal cancer.
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C
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Actual position
RCC tomo slices RMLO tomo slices
Right upper outer tumor R
Head
Scroll button
Scroll button Foot
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Lateral Medial
FIG. 2.19 Schematic of use of scroll button to identify the location for breast tumors on tomosynthesis. The ex- ample is in the upper outer quadrant. (A) Right craniocaudal (RCC) tomosynthesis slice shows a mass in the outer breast; the slice with the mass is second from the top or in the upper part of the breast. Thus the mass must be in the upper outer quadrant. (B) Right mediolateral oblique (RMLO) slice shows a mass in the upper breast; the slice with the mass is second from the lateral or outer part of the breast. Thus the mass must be in the upper outer quadrant. (C) Actual location of the mass in the upper outer right breast.
CC RL
Lateral Medial Lateral Medial
FIG. 2.20 Schematic showing a rolled lateral (RL) view predicting whether a lesion is located in the upper or lower part of the right breast. The initial craniocaudal (CC) view superimposes two lesions on each other (left).
When the top of the breast is rolled laterally (right), the superior lesion rolls laterally with the top of the breast tissue. The inferior lesion moves medially with the lower part of the breast tissue. Comparing whether the lesion moves laterally on the rolled CC lateral (RL) view with respect to the standard CC view will help predict whether the lesion is in the upper or lower part of the breast. (Modified from Sickles EA: Practical solutions to common mammographic problems: tailoring the examination, AJR Am J Roentgenol 151:31–39, 1988.)
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CC MLO
RL Spot lateral
Lateral
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FIG. 2.21 Rolled lateral (RL) view for localization of a finding. (A) Right craniocaudal (CC) view shows a density in the posterior medial aspect of the breast (arrow). (B) On the mediolateral oblique (MLO) view the mass was not seen at the time of interpretation. In retrospect, spiculation is seen extending into the lower part of the breast from outside the field of view at the edge of the film. (C) The lateral view does not show a definite mass at the time of interpretation. (D) A CC view with the top of the breast rolled laterally, ie, the rolled CC lateral (RL) view shows that the mass (arrow) is medial in comparison with that seen on the original CC view, indicating that it rolled medially with the lower part of the breast. (E) Spot compression in the lower portion of the breast reveals a spiculated mass (arrow). (F) Ultrasound directed to the lower portion of the breast shows a hypoechoic irregular mass that was diagnosed as invasive ductal cancer.
Normal asymmetries should have no suspicious calcifications, spiculations, or palpable masses, are stable when compared with older studies, and are composed of fibroglandular tissue.
An asymmetry may be abnormal or indicate cancer if it is pal- pable, has suspicious calcifications or spiculations, is new, or is a mass and not an asymmetry at all; if the patient has any of these findings with an asymmetry they should undergo a workup with ultrasound or biopsy.
The white parts of mammograms can hide masses. Radiologists can see masses if they are whiter than the surrounding tissue or if there is a round or spiculated mass edge projected against dark fat. If the radiologist sees a mass on one projection, the radiolo- gist looks for the mass on the orthogonal view. To do this, the radiologist measures the distance from the nipple to the mass and searches the orthogonal view for the mass at this distance
(see Fig. 2.16). If the finding is seen on two views, it is considered a mass or focal asymmetry. If the “mass” is seen on only one view, it is called an asymmetry or a density and represents either a summation artifact (Fig. 2.23) or a mass that is obscured on the second view (Fig. 2.24). The decision to recall this type of finding and prompt a workup is based on the radiologist’s experience and the degree of suspicion of the one-view finding.