Incidental Internal Mammary Lymph Nodes Visualized on Screening Breast MRI

Area of Science:

• Radiology
• Oncology
• Medical Imaging

Background:

• The frequency and size of internal mammary lymph nodes (IMLNs) in high-risk women undergoing screening breast MRI are not well-established.
• Lack of established normal size criteria for IMLNs can create management dilemmas when detected on staging MRI for breast cancer.

Purpose of the Study:

• To determine the average size and frequency of IMLNs in asymptomatic high-risk women undergoing screening breast MRI.
• To provide reference data for interpreting IMLNs detected during breast MRI.

Main Methods:

• Retrospective review of screening breast MRI scans from 108 high-risk women.
• Exclusion criteria included prior breast cancer, other thoracic malignancies, or prior thoracic radiation.
• Detailed recording of IMLN presence, size, location, and morphology.

Main Results:

• IMLNs were visualized in 50 out of 108 (46%) high-risk patients.
• The average size of visualized IMLNs was 4.5 mm (range, 2-9 mm).
• An average of 1-3 IMLNs were detected per patient, more frequently on the left and in the second/third intercostal spaces.

Conclusions:

• Approximately half of asymptomatic high-risk women exhibit 1-3 presumed normal IMLNs on screening breast MRI.
• These nodes typically measure between 2-9 mm, with a mean diameter of 4.5 mm.
• This data can aid in differentiating normal IMLNs from metastatic disease in this population.