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

Background Some reports suggest that there is a slightly higher frequency of breast cancer in the left breast com-pared 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 mam-mographic 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 cal-culated 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 cm3 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 com-position 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