Extramammary findings on breast MRI: prevalence and imaging characteristics favoring malignancy detection: a retrospective analysis.

BACKGROUND Little study of the extramammary finding of breast MRIs has been done with only descriptive work of the prevalence of location and malignancy. The purpose of the present study was to assess the prevalence, the location, and the imaging characteristics of the incidentally detected extramammary findings on breast MRI and to determine potential malignant characteristics. METHODS The study evaluated extramammary findings in 109 patients who underwent breast MRI for the staging of breast cancer and for the follow-up of post-therapy. Prevalence, the location, clinicopathologic findings of breast cancer size, metastasis, and MRI characteristics were evaluated retrospectively. Malignancy of extramammary findings was determined based on the pathologic examinations and diagnostic images. RESULTS One hundred forty-nine incidental findings were detected in 109 (4.6%) of 2361 patients, and 69 cases were confirmed or considered to be malignant. The most common site was the bone (43/149, 28.9%) with malignancy found in 30 (69.8%) of 43 bone lesions. Less frequent tumor locations were the liver (22.1%), lung (21.5%), pleura or chest wall (10.1%), mediastinum (6.7%), supraclavicular lymph nodes (LNs) (6.0%), and others (4.7%). Findings of significant relevance with malignancy of the extramammary findings included bigger size of breast cancer, presence of LN metastasis, and distant metastasis (P < 0.01). Lesions showing iso- or hypo signal intensity (SI) on T2-weighted imaging (T2WI) (P = 0.000), contrast enhancement (P = 0.000), high SI on diffusion-weighted imaging (DWI) (P = 0.049), low SI on apparent-diffusion-coefficient map relative to DWI (P = 0.000), and multiplicity (P = 0.000) of the extramammary finding were significantly related to malignancy. CONCLUSIONS Extramammary findings on breast MRI are not rare. Clinicopathologic features of the breast cancer and MRI features of extramammary findings could be useful in estimating the malignancy of the incidental extramammary finding.