Purpose
To compare magnetic resonance imaging (MRI) and ultrasound (US) for axillary lymph node (LN) staging in breast cancer patients in an observer-performance study.
Materials and Methods
An observer-performance study was conducted with five breast radiologists reviewing 50 consecutive patients of newly diagnosed invasive breast cancer with the use of ipsilateral axillary MRI and US. LN status was pathologically proved in all patients. Each observer reviewed the images in two separate sessions: one for MRI and the other for US. Observers were asked to indicate their confidence of the presence of at least one ipsilateral metastatic LN on a quasi-continuous rating scale and whether they recommend percutaneous biopsy preoperatively. Receiver operating characteristic (ROC) analysis and area under the ROC curve were used to characterize diagnostic performance. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated from whether observers recommended biopsy.
Results
There were no statistically significant differences in each observer’s performance between MRI and US, or in the performance of all observers as a group, in terms of ROC analysis. There were no statistically significant differences in sensitivity, specificity, PPV, or NPV between MRI and US, but there were statistically significant improvements in specificity and PPV from either MRI or US alone to MRI and US combined.
Conclusions
Observer performance on MRI and US are comparable for axillary LN staging. When US and MRI are concordant for positive findings, higher specificity and PPV can be obtained.
Axillary lymph node (LN) status is an extremely important prognostic factor for breast cancer patients, and it provides critical information for making treatment decisions . In the past, axillary LN dissection (ALND) was performed on all patients to both establish axillary LN status and treat metastatic LNs. However, because ALND can cause significant complications such as nerve injury, lymphedema, and arm weakness, sentinel LN biopsy (SLNB) has become the standard procedure for the assessment of axillary LN status . Although SLNB is less invasive than ALND because it removes fewer LNs, it is still a surgical procedure and carries risks such as lymphedema, seroma, and sensory parasthesias . If axillary LN staging can be established without surgical intervention, clinical management of patients could be significantly improved. For this purpose, preoperative LN staging with imaging has been investigated . Among multiple imaging modalities, ultrasound (US) and magnetic resonance imaging (MRI) are commonly used for assessment of axillary LNs in breast cancer patients . US is a portable examination and is useful in detecting abnormal axillary LN and for imaging guidance in percutaneous biopsy. MRI is useful in terms of assessing a large field of view, including the whole axillary region.
To our knowledge, there has not been a study that directly compares US and MRI in terms of ipsilateral axillary LN staging in an observer-performance study. Therefore, the purpose of this study is to compare, in an observer-performance study, MRI and US in their accuracy for axillary LN staging in breast cancer patients.
Materials and methods
Patients
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Table 1
Results of Pathologic Diagnosis
Final Pathology Total SLNB ALND Negative 34 0 34 Positive 2 14 16
ALND, axillary lymph node dissection; SLNB, sentinel lymph node biopsy.
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MRI Techniques
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Ultrasound Examination
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Observer Study
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Statistical Analysis
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Results
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Table 2
Area under the Receiver Operating Characteristic Curve Values and its Comparison between Magnetic Resonance Imaging (MRI) and Ultrasound (US)
Observers MRI US_P_ 1 0.741 ± 0.077 0.712 ± 0.079 .72 2 0.733 ± 0.080 0.727 ± 0.077 .92 3 0.740 ± 0.078 0.784 ± 0.067 .43 4 0.693 ± 0.083 0.701 ± 0.072 .91 5 0.767 ± 0.077 0.709 ± 0.080 .43 Average 0.732 ± 0.079 0.727 ± 0.075 — MRMC 0.726 ± 0.064 0.733 ± 0.068 .85
MRMC, multireader, multicase analysis.
Results for individual observers, estimate ± standard error; results for the average of all observers, average ± standard deviation; results for MRMC, estimate ± standard error.
P < .05 was considered statistically significant.
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Table 3
Average Sensitivity, Specificity, PPV, and NPV for MRI, US, and MRI and US Combined
MRI US MRI + US MRI or US 95% CIs (Average ± SD) MRI vs. US MRI vs. MRI + US US vs. MRI + US MRI vs. MRI or US US vs. MRI or US Sensitivity 60 ± 13 54 ± 8 49 ± 7 65 ± 15 (−6 to 23) (−28 to 0) (−13 to 0) (0 to 13) (0 to 28) Specificity 79 ± 11 81 ± 6 92 ± 6 68 ± 10 (−17 to 12) (4 to 25) ∗ (4 to 21) ∗ (−21 to −4) † (−25 to −4) † PPV 59 ± 9 58 ± 8 77 ± 10 49 ± 7 (−19 to 22) (3 to 35) ∗ (5 to 36) ∗ (−24 to −1) † (−22 to 1) NPV 81 ± 3 79 ± 3 79 ± 2 81 ± 5 (−4 to 9) (−8 to 3) (−3 to 4) (−4 to 4) (−3 to 9)
PPV, positive predictive value; NPV, negative predictive value; CI, confidence interval.
Note: Data shown are percentages.
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Table 4
Rate of Correct Diagnosis by Size of Metastatic Deposit in the Lymph Node
Metastatic Deposit (mm) Correct Diagnosis (%) N ∗ MRI US (Average ± SD) <5 40 ± 24 26 ± 12 7 5–10 60 ± 14 56 ± 17 5 >10 95 ± 11 100 ± 0 4
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Discussion
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Conclusions
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