A mammogram recall occurs when the initial screening image is incomplete or reveals a finding requiring further investigation. While receiving a recall notice can be anxiety-inducing, it is a relatively common occurrence in breast screening programs. The majority of individuals recalled for additional imaging do not have breast cancer; fewer than 10% of callbacks ultimately result in a cancer diagnosis. This process ensures that radiologists have enough information to make a definitive assessment, focusing here on a finding known as asymmetry.
Understanding Asymmetry in Mammography
Asymmetry in a mammogram refers to a localized area of increased density in one breast compared to the corresponding area in the other. This finding represents a difference in the density or structure of fibroglandular tissue. Unlike a distinct mass, an asymmetry typically lacks the convex borders and space-occupying characteristics of a lesion. It is merely an observation of unequal tissue distribution.
The finding may be visible on one mammographic projection (an “asymmetry”) or on two different projections (a “focal asymmetry”). In either case, it represents an inconclusive result. Since the finding is not definitively benign or malignant based on the initial image, the radiologist assigns the study a Breast Imaging-Reporting and Data System (BI-RADS) category 0. This category indicates that the image is technically incomplete and mandates a recall for additional views to clarify the nature of the density.
Common Benign Explanations for Asymmetry Recalls
Summation Artifact
The most frequent reason for an asymmetry recall is summation artifact, which is not a true abnormality within the breast tissue itself. This occurs when normal, overlapping layers of glandular tissue are compressed and projected onto the two-dimensional mammogram film, mimicking a dense area. When the breast is repositioned and compressed differently during the follow-up diagnostic exam, this artifact often disappears completely.
Normal Tissue Variation
Normal variations in the natural distribution of glandular tissue are a common benign cause for asymmetry. Breasts are not perfectly symmetrical, and one breast may contain more fibroglandular tissue than the other. This difference is considered a normal anatomic variant, especially when it involves a large area of the breast, which is referred to as global asymmetry.
Hormonal and Technical Factors
Hormonal fluctuations frequently contribute to temporary or changing asymmetries, particularly in premenopausal individuals. Cyclical changes associated with the menstrual cycle can cause breast tissue to swell or become denser, appearing as a new or more conspicuous asymmetry. Other hormonal influences, such as those from hormone replacement therapy, can similarly affect tissue density and lead to a recall. Technical factors related to patient positioning during the initial screening can also generate an apparent asymmetry, such as a slight rotation or variation in tissue captured between the two sides. Non-cancerous conditions like fibrocystic changes, localized scar tissue, or benign growths can also present on the image as an asymmetric density.
Diagnostic Procedures Following an Asymmetry Recall
When a screening mammogram yields a BI-RADS 0 for asymmetry, the next step is a diagnostic mammogram to specifically evaluate the area of concern. The radiologist will order specialized, targeted views, such as spot compression views, which apply localized pressure to the suspected area. This technique is highly effective because it helps to spread out the tissue, which either confirms the presence of a real lesion or, more often, causes the summation artifact to dissipate.
Magnification views may also be used to obtain a higher-resolution image of the area, allowing the radiologist to better assess the margins and internal characteristics of the density. Following the specialized mammography views, the radiologist will often use a targeted breast ultrasound to further investigate the asymmetric area. Ultrasound provides real-time images and is exceptional at distinguishing between a solid mass and a simple fluid-filled cyst, which may have appeared dense on the mammogram.
After these additional imaging tests, the radiologist will assign a final BI-RADS score. If the asymmetry is confirmed to be a summation artifact or a known benign finding, the patient is returned to routine annual screening. If the finding persists but is determined to be likely benign, a short-term follow-up mammogram, typically in six months, may be recommended to ensure stability. In the rare instance that the asymmetry appears suspicious even after the diagnostic workup, a biopsy may be recommended for a definitive diagnosis.