Incidental internal mammary lymph nodes visualized on screening breast MRI

OBJECTIVE. The frequency of visualization and size of internal mammary lymph nodes in women undergoing high-risk screening breast MRI is unknown. When these nodes are discovered on staging MRI of newly diagnosed breast cancer patients, management could present a treatment dilemma because normal size criteria do not exist. The aim of this study was to establish the average size and frequency of internal mammary lymph nodes observed in asymptomatic high-risk women undergoing screening breast MRI. MATERIALS AND METHODS. We conducted a retrospective review of 108 women at high risk for breast cancer who underwent screening breast MRI between January 2010 and January 2014. Patients with new or previous diagnosis of breast cancer, prior nonbreast malignancy affecting the thorax or mediastinum, or previous radiation to the thorax were excluded. The presence, diameter, laterality, intercostal space, relationship to the internal mammary vessels, age, morphology, and clinical history of internal mammary lymph nodes were recorded. RESULTS. Internal mammary lymph nodes were visualized in 50 of 108 high-risk patients, with an average size of 4.5 mm (range [± SD], 2-9 ± 1.59 mm). In the 50 women who had internal mammary lymph nodes visible on MRI, an average of 1.4 nodes (range, 1-3 nodes) were present. Internal mammary lymph nodes were more frequently visualized on the left (p < 0.001), at the second and third intercostal spaces (p = 0.007), and medial to the internal mammary vessels (p < 0.001). CONCLUSION. In this small cohort, 1-3 presumed normal internal mammary lymph nodes measuring 2-9 mm (mean diameter 4.5 mm) were detected in about half of asymptomatic high-risk women presenting for screening MRI of the breasts.