Prevalence of extramammary findings on breast MRI: a large retrospective single-centre study.

[PURPOSE] This study sought to determine the prevalence of extramammary findings on magnetic resonance (MR) imaging of the breast.

[MATERIALS AND METHODS] We retrospectively reviewed the data sets of 828 consecutive patients (F/M; 821/7; mean age, 50 ± 11 years) who underwent breast MR imaging. The most common clinical indication was assessment of lesion extent in patients with known breast tumour (n=380, 46%), characterisation of equivocal findings at conventional imaging (n=331, 40%), evaluation of women at high risk for breast cancer (n=43, 5%) and following breast augmentation therapy (n=74, 9%).

[RESULTS] Collateral findings were found in 282/828 (34%) patients. In those 282 patients, 480 incidental lesions were detected. The most common localisation was the liver (231/480; 48%). Of the 480 collateral findings, 66 (14% in 38 patients) were classified as significant and deserving further investigation. These comprised 26 metastatic bony lesions, 15 mediastinal/axillary lymph nodes, six metastatic lung lesions, five metastatic liver lesions, four pneumonitis, two aneurysms of the ascending aorta, two adrenal adenomas, one neurofibroma of the back, one multiple myeloma, one mediastinal lymphoma, one sternal amyloidosis, one left ventricular dilatation and one trapezium lipoma.

[CONCLUSIONS] There is a high prevalence of extramammary findings on breast MR imaging. Evaluation of the examination should focus not only on the breast fields but also consider extramammary findings to avoid inappropriate management and possible legal issues.