Objectives: Incidental extra-mammary findings in breast Magnetic Resonance Imaging (MRI) may be benign in nature, but may also represent a metastasis or another important lesion. We aimed to analyse the prevalence and clinical relevance of these unexpected findings.
Methods: A retrospective review of 1535 breast MRIs was conducted. Only axial sequences were reassessed. Confirmation examinations were obtained in all cases.
Results: 285 patients had a confirmed incidental finding, which were located in the liver (51.9%), lung (11.2%), bone (7%), mediastinal lymph nodes (4.2%) or consisted of pleural/pericardial effusion (15.4%). 20.4% of incidental findings were confirmed to be malignant. Positive predictive value for MRI to detect a metastatic lesion was high if located within the bone (89%), lymph nodes (83%) and lung (59%), while it was low if located within the liver (9%) or if it consisted of pleural/pericardial effusion (6%). The axial enhanced sequence showed superior sensitivity to unenhanced images in detecting metastatic lesions, especially if only smaller (≤10 mm.) lesions were considered.
Conclusions: The prevalence of metastatic incidental extra-mammary findings is not negligible. Particular attention should be to incidental findings located within the lung, bone and mediastinal lymph nodes.