A routine screening mammogram recall for “asymmetry” is a frequent cause of anxiety. An asymmetry finding means that an area of tissue in one breast does not match the corresponding area in the other, or has changed from a previous exam. The purpose of this further evaluation is to clarify the nature of this density difference. This process is a standard part of breast cancer screening, ensuring the radiologist can definitively determine if the finding represents a normal variant or requires more attention.
Defining Mammographic Asymmetry
Mammographic asymmetry is defined by radiologists as a unilateral area of increased fibroglandular density that does not possess the convex margins or three-dimensional shape of a true mass. It represents a difference in the amount or arrangement of normal breast tissue between the two sides. Radiologists use specific classifications to describe this finding, which guides the need for a recall.
A basic “asymmetry” is a density seen only on one mammographic view, often resulting from tissue overlap during compression. A “focal asymmetry” is more localized and visible on two different views, suggesting a true concentration of tissue. “Global asymmetry” describes a large area of increased density, often spanning more than a quarter of the breast, and is usually considered a normal variation if static. These distinctions help the reading radiologist assess the level of suspicion and determine the appropriate next step for the patient.
Common Benign Explanations for Asymmetry Findings
The majority of asymmetry recalls are ultimately confirmed to be benign. The most common cause for an asymmetry on a screening mammogram is the superimposition of normal breast tissue, sometimes called a summation artifact. This occurs when glandular and fibrous tissues overlap in the two-dimensional X-ray image, creating the illusion of a denser area that is not actually present.
Normal variations in breast tissue density are also frequent contributors. Breasts naturally possess an uneven composition, and an asymmetry may reflect non-uniform involution, where glandular tissue regresses at different rates. Hormonal fluctuations related to the menstrual cycle or hormone replacement therapy can also cause temporary, localized changes in tissue density.
Specific non-cancerous conditions are also responsible for many focal asymmetries. Benign masses like cysts, which are fluid-filled sacs, or fibroadenomas, which are solid tumors, can appear as dense spots on a mammogram. Technical or positional issues during the initial screening can also cause a fold or bunching of tissue, leading to an apparent asymmetry that disappears when the breast is re-imaged with a slight adjustment in positioning.
When Asymmetry Requires Further Investigation
While most asymmetries are benign, certain characteristics raise concern and necessitate additional evaluation. The most significant is the “developing asymmetry,” which is an area of increased density that is either entirely new or has become distinctly larger or more conspicuous since previous mammograms. Since breast density generally decreases with age, a developing asymmetry is viewed with greater suspicion because it represents a change over time rather than a static finding.
A developing asymmetry is associated with malignancy, and a significant percentage of these findings require a biopsy. Suspicion increases if the asymmetry is accompanied by other features associated with cancer. These features include architectural distortion, which is a pulling in or spiculation of the surrounding tissue without a clearly defined mass.
Another concerning co-finding is the presence of suspicious microcalcifications within the area of asymmetry. Microcalcifications are tiny calcium deposits, and while most are benign, a new cluster of fine, pleomorphic (irregularly shaped) calcifications can signal a precancerous or early cancerous process. If the asymmetry corresponds to a palpable lump that the patient or clinician can feel, this clinical correlation also increases the need for a prompt diagnostic workup.
The Diagnostic Follow-up Procedures
A recall appointment for asymmetry involves a focused series of imaging tests designed to resolve the initial finding. The first step often includes a diagnostic mammogram, which uses specialized views such as spot compression and magnification. Spot compression applies pressure to a smaller, targeted area, helping to spread out the tissue and confirm if the density is real or just overlapping tissue.
Following the diagnostic mammogram, a breast ultrasound is performed to further characterize the area of concern. The ultrasound uses sound waves to determine if the asymmetric area is solid tissue, which warrants more scrutiny, or a simple fluid-filled cyst. The ability of the ultrasound to distinguish between solid and fluid-filled structures is often the key step in classifying the finding as benign.
If the diagnostic imaging remains inconclusive, or if the findings possess suspicious characteristics, the final step may be a biopsy. A biopsy involves using a needle guided by imaging (either mammography or ultrasound) to take a small sample of the tissue for laboratory analysis. This process provides a definitive diagnosis by identifying the cellular composition of the asymmetric area.