This figure illustrates that the left breast is asymmetric when compared to the right breast. This patient had radiation therapy to the left hemithorax as a child and, subsequently, she had hypoplasia of the left breast. And this is a good illustration of assymetic breast tissue.

The second type of breast asymmetry is architectural distortion. Um ... this is where one finds the focal area of architectural distortion where there are spiculations which radiate from a central point. Um ... and there's usually associated attraction of normal breast parenchyma around this area.

This mammogram is a nice illustration of architectural distortion. It shows the spiculation and the retraction of normal breast parenchyma. On biopsy, this lesion actually turned out to be a radial scar which is one of the benign causes of architectural distortion. The third type of asymmetry that's encountered is a focal density seen in one projection. And as the name describes, this is a density that's only seen on one routine mammographic view. Um ... this can be either because ... uh, there's a summation of superimposed breast tissue that appear as a focal density on one projection, or in the case of a true lesion, uh, the lesion may be obscured by overlying fibroglandular tissue on the other view versus ... it may simply be out of the field of view. In this illustration, one can see a focal area of asymmetry in the apparent axillary tail of the left breast.

With additional imaging, this area actually was found to be medial in location and represented medullary carcinoma on breast biopsy.

The fourth type of breast asymmetry that one can encounter is called a focal asymmetric density. This is a density that's seen on two standard mammographic views but cannot be accurately categorized as a mass. Um ... this figure illustrates a prominent asymmetric density that's seen in the left breast which had been followed for four years and was found to represent benign breast tissue. In addition to having a fundamental understanding of the ACR-Lexicon of the different types of breast asymmetries and distortions, it's equally important to understand the proper work-up of these findings. Um ... supplementary breast imaging with additional mammographic views, such as the off-angle view and spot compression, in addition to sonographic evaluation of these lesions can often be very helpful in diagnosing these findings.

Spot compression views can also show whether a density actually persists, representing a true lesion, and if so, to better characterize its shape and margins

However, there are limitations to the spot compression view. If a lesion is clearly seen on two mammographic views, and is less prominent, or less dense on the spot compression view, this shouldn't dissuade one from working it up. Uh ... actually sometimes spot compression displaces overlying fibroglandular tissue making a small lesion less prominent or less dense.

Finally, ultrasound is an invaluable tool in assessing breast asymmetries and distortions. It can help identify whether a lesion is actually a true solid mass versus a cystic lesion. If one finds that a lesion is a suspicious hypoechoic shadowing mass, then this would prompt further investigation, or biopsy. Whereas, if the ultrasound actually shows a simple cyst, then this would prompt routine follow-up.

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