title: Incidental Internal Mammary Lymph Nodes Visualized on Screening Breast MRI.
abstract: 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.
  
  
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: 1 Penn State College of Medicine, 500 University Dr, Hershey, PA 17033.
authors.forename: Meghan
authors.initials: M
authors.lastname: Mack
authors.affiliation: 2 Department of Radiology, Penn State Milton S. Hershey Medical Center, Penn State Hershey Breast Imaging, Hershey, PA.
authors.forename: Alison
authors.initials: A
authors.lastname: Chetlen
authors.affiliation: 3 Division of Biostatistics and Bioinformatics, Penn State Hershey Cancer Institute, Penn State College of Medicine.
authors.forename: Jason
authors.initials: J
authors.lastname: Liao
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000473:pathology; D003287:Contrast Media; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D033162:Incidental Findings; D008198:Lymph Nodes / Q000033:anatomy & histology*; D008207:Lymphatic Metastasis / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008403:Mass Screening; D008875:Middle Aged; D012189:Retrospective Studies
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA
keywords: breast MRI; internal mammary lymph nodes; normal values; screening