Background: The concept of natural breast asymmetry is well known; however, actual documentation in the literature is limited. New technology is currently available which provides 3-dimensional surface images of the breast and the ability to qualitatively determine differences in breast size, shape, and contour. The purpose of this report is to objectively determine the extent to which this natural breast asymmetry exists.
Methods: Eighty-seven women without a history of breast cancer or previous breast surgery were included. Images were obtained using 3dMD technology. Data points queried included age, parity, body mass index (BMI), ethnicity, and bra size. Left/right images were superimposed and the distance between the 2 surfaces, and contour was calculated. The degree of asymmetry was determined and comparisons were made. Similar differences in nipple-to-notch measurements were calculated and compared. Subjective evaluations were included for clinical relevance.
Results: The average age was 49.6 years (range: 19-77), with an average BMI of 25 (range: 18.5-36.7). The average nipple to notch on the left was 24.3 cm and 23.8 cm on the right. The nipple-to-notch asymmetry was on average 3.2%, with the left breast measurement being greater the majority of the time (62%). The mean distance between each breast demonstrated consistent breast asymmetry, with an average measurement of +0.5 mm (left breast being larger than the right). The degree of breast asymmetry was documented by a root mean square value (RMS) of 5.93 mm. This was not related to age, parity, or ethnicity; however, it was significantly higher in those patients with larger BMI, cup size, and chest-wall circumference. Only 10% of women were found to have severe breast asymmetry on subjective evaluation, which correlated objectively with the RMS in that group being significantly higher at 9.8 mm (P < 0.05). There were no predictable patterns of asymmetry; however, the most common pattern was larger laterally and smaller medially, found in 32% of the women.
Conclusion: Natural breast asymmetry does exist, demonstrated objectively using 3-dimensional surfaces images. The left breast is on average larger than the right, with differences in size and shape being consistent but fairly unpredictable. It is important that we know baseline differences in breast symmetry prior to objectively analyzing results following esthetic and reconstructive breast surgery.