Bilateral symmetry of breast tissue composition by magnetic resonance in young women and adults

Abstract

Background: Some reports suggest that there is a slightly higher frequency of breast cancer in the left breast compared with the right in middle-aged women. The reasons for this association are unknown. The water and fat content of both breasts was compared using magnetic resonance (MR). Breast water by MR reflects fibro-glandular tissue and is strongly positively correlated with percent mammographic density, a strong risk factor for breast cancer.

Methods: Magnetic resonance was used to measure fat and water content of the breast in 400 young women aged 15-30 years and a random sample of 100 of their mothers. All MR examinations were carried out using a 1.5T MR system, and 45 contiguous slices were obtained in the sagittal plane. One reader identified the breast tissue in the image, and subsequently, fat and water content was calculated using a three-point Dixon technique. Left- and right-sided images were read independently in random order.

Results: In young women, mean percent water was on average 0.84 % higher in the right compared with the left breast (p < 0.001) and total breast water was on average 6.42 cm(3) greater on the right side (p < 0.001). In mothers, there were no significant differences in any breast measure between right and left sides.

Conclusion: The small differences in breast tissue composition in young women are unlikely to be associated with large differences in breast cancer risk between sides. The reported excess of left-sided breast cancer in older women is unlikely to be explained by differences in breast tissue composition.

Fig. 1

a Inter-reader reliability of measurements. b Intra-reader reliability of measurements. Lines were obtained using univariable linear regression

Fig. 2

Box-plots comparing the a daughters’ (n = 400) and b mothers’ (n = 100) percent water content of the left breast versus right breast

Fig. 3

Bland–Altman plot displaying the relative difference in percent water between the left and right breasts for daughters using untransformed values (n = 400)

Fig. 4

Bland–Altman plot displaying the relative difference in percent water between the left and right breasts for mothers using untransformed values (n = 100)