Abstract
The aim of this study was to determine the range of apparent diffusion coefficient (ADC) values for benign axillary lymph nodes in contrast to malignant axillary lymph nodes, and to define the optimal ADC thresholds for three different ADC parameters (minimum, maximum, and mean ADC) in differentiating between benign and malignant lymph nodes. This retrospective study included consecutive patients who underwent breast MRI from January 2017–December 2020. Two-year follow-up breast imaging or histopathology served as the reference standard for axillary lymph node status. Area under the receiver operating characteristic curve (AUC) values for minimum, maximum, and mean ADC (min ADC, max ADC, and mean ADC) for benign vs malignant axillary lymph nodes were determined using the Wilcoxon rank sum test, and optimal ADC thresholds were determined using Youden’s Index. The final study sample consisted of 217 patients (100% female, median age of 52 years (range, 22–81), 110 with benign axillary lymph nodes and 107 with malignant axillary lymph nodes. For benign axillary lymph nodes, ADC values (×10−3 mm2/s) ranged from 0.522–2.712 for mean ADC, 0.774–3.382 for max ADC, and 0.071–2.409 for min ADC; for malignant axillary lymph nodes, ADC values (×10−3 mm2/s) ranged from 0.796–1.080 for mean ADC, 1.168–1.592 for max ADC, and 0.351–0.688 for min ADC for malignant axillary lymph nodes. While there was a statistically difference in all ADC parameters (p<0.001) between benign and malignant axillary lymph nodes, boxplots illustrate overlaps in ADC values, with the least overlap occurring with mean ADC, suggesting that this is the most useful ADC parameter for differentiating between benign and malignant axillary lymph nodes. The mean ADC threshold that resulted in the highest diagnostic accuracy for differentiating between benign and malignant lymph nodes was 1.004×10−3 mm2/s, yielding an accuracy of 75%, sensitivity of 71%, specificity of 79%, positive predictive value of 77%, and negative predictive value of 74%. This mean ADC threshold is lower than the European Society of Breast Imaging (EUSOBI) mean ADC threshold of 1.300×10−3 mm2/s, therefore suggesting that the EUSOBI threshold which was recently recommended for breast tumors should not be extrapolated to evaluate the axillary lymph nodes.
Highlights
Unspecific axillary lymphadenopathy is often encountered in breast imaging
While significant differences were observed when comparing the median values all apparent diffusion coefficient (ADC) parameters between benign and malignant axillary lymph nodes, results show that there is a significant overlap of ADC values of benign and malignant nodes
The least overlap in ADC values occurred with mean ADC, suggesting that this is the most useful ADC parameter for differentiating between benign and malignant axillary lymph nodes
Summary
Unspecific axillary lymphadenopathy is often encountered in breast imaging. It may be caused by various benign conditions [1, 2] or more recently after COVID-19 vaccinations [3, 4]; patients with a personal history or concurrent diagnosis of breast cancer in particular can pose a diagnostic dilemma. Sentinel lymph node biopsy is a standard procedure in early-stage breast cancer patients with clinically negative axillary lymph nodes [7], with a reported sensitivity of 58%–72% [8,9,10] and accuracy of 75% [11] While it is a minimally invasive procedure, it is associated with several morbidities, e.g., lymphedema (8.2%) [12], seroma (19.5%), localized swelling, pain and paresthesia, infectious neuropathy, decreased arm strength, and shoulder stiffness [13]. In both scenarios of lymphadenopathy with and without a personal history of breast cancer, the use of a non-invasive imaging technique for the accurate assessment of axillary nodal status is desirable. Prior studies evaluating the axilla with MRI have reported a mean accuracy of only 75% (range, 71%–85%) in predicting axillary metastasis [17,18,19]
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