Management of MRI-Detected Benign Internal Mammary Lymph Nodes

Abstract

Introduction In this retrospective study, we aimed to evaluate benign internal mammary lymph nodes (IMLNs) in terms of frequency, number, size, long axis/short axis (L/S) ratio, intercostal location, presence of fatty hilum, and stability using breast magnetic resonance imaging (MRI) and discuss the findings by reviewing existing literature. Methods This single-center study consisted of 130 women between the ages of 24 and 76 years, who had at least two breast MRI examinations in our institution, with the latest exam performed between January 1, 2019 and November 1, 2019, were eligible for the study. MRIs of the study group were independently reviewed by two radiologists. Results IMLN was detected in 31.1% of the 427 MRIs, with a total number of 256 nodes. The most common indication for breast MRI was high-risk screening (66.2%). The median number of nodes per patient was 1 (range: 1-6). The median follow-up time was 19.5 months (range: 6-141 months). None of these benign nodes showed significant interval growth. Mean L/R ratio of the nodes was 1.9. One hundred and four nodes ( n = 104, 40.6%) had a L/S ratio less than 2 and 43.2% ( n = 45) of the nodes with a L/S ratio less than 2, had a long axis measuring less than or equal to 3mm. IMLN of patients with breast implants had the largest mean long axis. The fatty hilum was identified in 34.3% ( n = 68) of the 256 nodes. The size of the lymph nodes where fatty hilum was visualized was significantly larger than the ones where fatty hilum was not visualized ( p < 0.001). Fatty hilum could be visualized in only 2.7% of the nodes with a long axis smaller than 3 mm. Conclusion IMLN is a frequent finding on breast MRI. We have shown that benign IMLNs might be large sized in specific cases like patients with breast implants. When small sized (≤3mm), they are more likely to be rounded (L/S ratio <2). The fatty hilum that is a feature of benignity might not be visualized in nodes less than or equal to3mm.

Keywords: MRI; breast cancer; high risk; internal mammary lymph node; screening.

Fig. 1

Axial plane, postcontrast magnetic resonance image of a right-sided internal mammary lymph node in the second intercostal space, which measures 8 × 3 mm. The low intensity fatty hilum is clearly seen (arrow).

Fig. 2

Each bar on the x-axis indicates the number of nodes. The frequency (a.k.a. the number of cases) levels regarding for each bar are represented on the y-axis.

Fig. 3

Comparison of the long axis size of nodes in patients with and without fatty hilum. The y-axis indicates the size of the long axis. The horizontal lines in the middle of each box indicate the median, while the top and bottom borders of the box mark the 25th and 75th percentiles, respectively. The whiskers above and below the box mark the maximum and minimum levels of node sizes.