3D mammography (digital breast tomosynthesis or DBT) is an advanced imaging technique that uses low-dose X-rays to create three-dimensional breast images, aiding in early detection and diagnosis. A common finding on these mammograms is focal asymmetry, which describes an area of breast tissue appearing denser or different from surrounding tissue on at least two views, but without the distinct features of a clear mass. While often requiring further evaluation, focal asymmetry is frequently not indicative of cancer.
Understanding Focal Asymmetry
Focal asymmetry refers to a localized area within one breast that shows increased tissue density compared to the corresponding area in the other breast. Unlike a true mass, which typically has convex borders and occupies a three-dimensional space, focal asymmetry lacks these defined margins and may only be visible on certain mammographic views. It represents breast tissue that doesn’t perfectly align with normal architecture, yet isn’t a definitive mass.
3D mammography is particularly effective at detecting these subtle changes compared to traditional 2D mammography. The 3D system captures multiple X-ray images from various angles, which are then reconstructed by a computer into a detailed, three-dimensional view. This layered approach minimizes overlapping breast tissue, which can obscure abnormalities on 2D images, allowing radiologists to better distinguish subtle changes.
Benign Reasons for Focal Asymmetry
Many instances of focal asymmetry are due to non-cancerous conditions. The most frequent cause is simply normal overlapping breast tissue, where the arrangement of healthy structures can appear denser when viewed from specific angles during the mammogram. This phenomenon, sometimes called a summation artifact, occurs when normal tissues are superimposed.
Hormonal changes throughout a woman’s life can also influence breast density and contribute to focal asymmetry. Fluctuations during the menstrual cycle, pregnancy, or hormone replacement therapy can temporarily alter the breast’s appearance on imaging. Fibrocystic changes, common breast conditions involving cysts, fibrosis, and glandular tissue changes, are another benign cause. These changes can present as areas of increased density on a mammogram.
Scar tissue from previous breast surgeries, biopsies, or injuries can also manifest as focal asymmetry. This tissue can vary in appearance, sometimes mimicking more concerning findings. Inflammation or infection within the breast, such as mastitis or an abscess, may also lead to localized areas of increased density. Fat necrosis, a benign condition from breast trauma or previous procedures, can also appear as focal asymmetry or even masses resembling cancer.
Concerning Findings and Atypical Changes
While often benign, focal asymmetry can occasionally indicate more serious underlying conditions. Early-stage breast cancer, particularly invasive ductal carcinoma or invasive lobular carcinoma, may sometimes present as a subtle architectural distortion or focal asymmetry rather than a clearly defined mass. These subtle changes are sometimes the only visible sign of a developing cancer.
Ductal Carcinoma In Situ (DCIS), involving pre-invasive cancer cells within milk ducts, might also appear as focal asymmetry, often with microcalcifications. Atypical ductal hyperplasia (ADH) and atypical lobular hyperplasia (ALH) are benign conditions with abnormal cell growth in breast ducts or lobules. While not cancerous, they increase future cancer risk and can appear as asymmetry.
Certain benign lesions can also mimic cancer on imaging and present as focal asymmetry. Radial scars, also known as complex sclerosing lesions, are non-cancerous areas of hardened breast tissue that can appear as architectural distortion on a mammogram. These lesions are not true scars but can be difficult to distinguish from cancer due to their appearance. These findings necessitate further investigation to differentiate them from malignancy.
Next Steps in Evaluation
A finding of focal asymmetry on a 3D mammogram often prompts additional diagnostic steps to determine its nature. This typically begins with additional mammographic views, such as targeted compression views or spot magnification, to better characterize the area of concern. These specialized views help radiologists assess if the asymmetry is due to overlapping tissue or a true underlying change.
Following this, a breast ultrasound is commonly performed. Ultrasound can help determine if the asymmetry corresponds to a solid mass, a fluid-filled cyst, or normal breast tissue that appeared dense on the mammogram. For some cases, if other imaging remains inconclusive or if there are other high-risk factors, a breast MRI may be recommended for further evaluation. These advanced imaging techniques provide different perspectives, aiding in a more comprehensive assessment.
If the focal asymmetry persists or exhibits suspicious features after these additional imaging studies, a biopsy may be recommended. A biopsy involves obtaining tissue for pathological examination, definitively determining if cells are benign or malignant. Common biopsies include core needle biopsy (removing small tissue cylinders) or vacuum-assisted biopsy (using suction for multiple samples). In some low-suspicion cases, a short-interval follow-up mammogram, typically in 6 months, may be suggested to monitor for stability or changes over time.