By: Randal L. Aschenbeck, MD
Breast Imaging Radiologist with Austin Radiological Association (ARA)
Reading a mammogram is difficult. Doctors that read mammograms are radiologists. They complete 4 years of medical school, 1 year of internship, and 4 years of residency. Some radiologists also complete an additional year of training to read mammograms; called a fellowship. In addition, in order to maintain their certification to read mammograms, they must read a federally mandated minimum number of mammograms. What follows is a brief summary of some of the things radiologists look for when interpreting your mammogram.
A routine or screening mammogram is composed of 4 images. Each image is obtained by passing a very small amount of radiation through the breast. This radiation forms a picture on the detector on the other side of the breast. There is a mediolateral oblique (MLO) view which is looking through your breast from the side. In addition, there is a craniocaudal (CC) view which is looking through your breast from above. A screening mammogram is composed of a CC and MLO view of each breast. Screening mammograms should only be performed on women that do not have an area of concern. If a woman is having a mammogram to evaluate an area of concern, then a diagnostic mammogram, which usually involves different views and possibly an ultrasound, is required.
Digital tomosynthesis, also known as 3-D mammography, is a relatively new application of technology that can be used for breast cancer screening. Digital tomosynthesis images are obtained by passing a small amount of radiation through the breast at different angles. A series of images are reconstructed that allow the radiologist to scroll through the breast, similar to a CT scan. The amount of radiation exposure during a digital tomosynthesis examination is only slightly higher than a digital mammographic study, and far below FDA limits. Images are obtained in the CC and MLO projections for each breast just as in digital mammography. Digital tomosynthesis is more sensitive and specific for detecting breast cancer. This means that more breast cancers are found and fewer women need to be called back for additional images from a screening mammogram. Digital tomosynthesis can provide a benefit to most women but is especially useful in women with a history of breast conserving therapy,(lumpectomy due to breast cancer diagnosis), or women undergoing their first (also known as a baseline) mammogram. There is a common misconception that less, or even no, compression is needed for digital tomosynthesis. This is untrue. Just as in digital mammography, compression is extremely important with tomosynthesis.
Initially, the mammographic images are evaluated for quality. Are the breasts positioned appropriately? Was there motion during the image taking process resulting in a blurry image? Are there artifacts on the image? These issues could potentially cause a cancer to be missed. Occasionally, a patient will be called back for more images simply because of one of these technical reasons.Subsequently, the radiologist will inspect the images looking for abnormalities in the form of masses, calcifications, asymmetries, and architectural distortion. These will be explained in further detail. In addition, the radiologist will compare your current mammogram with your prior mammograms. Your prior mammograms are extremely important. If you have prior mammograms make sure they are made available to the radiologist reading your current mammogram. Changes on a mammogram due to cancer can be very subtle, only detected by noticing a change on a prior mammogram. Stability is also an important factor when reading a mammogram and underscores the importance of having prior studies. Radiologists want to see at least 2 years of stability when deciding if a finding is benign or needs additional workup.
Masses are defined as “3-dimensional and occupy space with completely or partially convex-outward borders.” If a new mass is identified, a diagnostic evaluation maybe warranted. Additional images are obtained to further evaluate the shape, margin, and density of the mass. The margin of the mass is its border. The density is how bright the mass looks on the mammogram compared to the surrounding breast tissue. An ultrasound may also be obtained at the time of the diagnostic evaluation to determine if the mass is solid or a benign (noncancerous) cyst.
Figure 1: Mass demonstrated in the lower outer quadrant of the left breast. The top image is an MLO view and the bottom image is a CC view.
Calcifications are deposits of calcium salts in the breast. Calcifications are common and there are many reasons why they form within the breast. Luckily, most of these reasons are benign. Sometimes calcifications within the breast can be associated with cancer. Certain characteristics of the calcifications help a radiologist decide if further action is warranted. Magnification views are obtained for calcifications that need further imaging to assess the shape and the distribution of the calcifications.
Figure 2: Example of calcifications within the breast.
Architectural distortion is when the normal breast tissue appears distorted without definite mass. This can look like thin straight lines radiating from a central point or retraction seen at the edge of the breast tissue. Additional images may be obtained to help decide if the distortion is normal overlapping tissue, if there is an associated mass, and where exactly the distortion is in the breast. It is common to see distortion on only one of the images. You need images obtained at different projections to know exactly where an abnormality is in the breast.
Figure 3: Architectural distortion within the breast. Notice the thin straight lines radiating from a central point.
An asymmetry is defined as “a unilateral deposit of fibroglandular tissue not conforming to the definition of a radiodense mass.” This basically means an area of the breast that looks different compared with the other breast. There are four types of asymmetries; asymmetry, focal asymmetry, global asymmetry, and developing asymmetry. An asymmetry is seen on only one mammographic image. A focal asymmetry is seen in two images, but lacks the outward border or a mass. A global asymmetry is similar to a focal asymmetry but occupies more than one quadrant of the breast. A developing asymmetry is a focal asymmetry that is new or more conspicuous when compared with the previous mammograms. Additional images maybe obtained to see if an asymmetry is real or merely overlapping tissue and determine exactly where it is located. Ultrasound may also be performed at that time to better characterize the asymmetry.
Figure 4: Asymmetry seen in the left breast. No corresponding abnormality seen on the MLO view.
Reading a mammogram is difficult. This was just a quick synopsis of some of the things radiologists look at while reading your mammogram and is by no means a complete list. If you should have questions about your mammogram, please do not hesitate to contact your radiologist.
At the BCRC, we can connect you with community partners that provide free or sliding scale screening and diagnostic services for those that qualify. Please email us at firstname.lastname@example.org.
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