AJR: Breast MRI protocol opens door to lymph node assessment
The presence of axillary lymph node metastases wields a significant impact on prognosis and management of breast cancer. However, imaging has played a limited role. Instead, surgical sampling or clearance of axillary lymph nodes, which is associated with long-term morbidity and side effects, serves as the standard of care.
“[T]he use of MRI for the evaluation of axillary lymph nodes remains controversial,” wrote Pascal A. T. Baltzer, MD, from the Institute of Diagnostic and Interventional Radiology at Friedrich-Schiller-University Jena in Jena, Germany. Scans acquired using dedicated breast coils do not allow complete bilateral assessment of the axillary lymph nodes. Although additional scans can provide an accurate assessment of the region, the time required for scanning is not clinically feasible.
Baltzer and colleagues designed a prospective study to determine whether an extended mammography MRI (MRM) protocol for fast bilateral scanning of both breasts, both axillae and the supraclavicular region could differentiate nodal positive and nodal negative breast cancers.
The researchers recruited 56 primary breast cancer patients referred for preoperative local staging and used surgical verification as the reference standard for locoregional staging. The MRI protocol consisted of a conventional MRM protocol and two additional sequences to cover all locoregional lymph nodes and adjacent compartments of lymphatic drainage.
Two radiologists with significant breast MRI experience independently read the studies and assessed ipsilateral lymph nodes using predefined quantitative and qualitative descriptors, including BI-RADS descriptors.
Studies were successfully acquired in all patients, and the interrater agreement for nodal staging was “almost perfect,” reported the researchers.
“Our study results show that axillary staging can be combined with a conventional MRM examination using a dedicated whole-body scanner. …The data are of clinical importance because they could help to solve a diagnostic dilemma, i.e. to accurately perform noninvasive N-staging without significantly increasing scanning time,” wrote Baltzer. The approach provides high reliability and accuracy, the researchers emphasized.
Baltzer and colleagues credited the whole-body scanner with enabling coverage of the appropriate field of view as well as providing fast acquisition. They also noted that using the descriptor “asymmetry,” which had been excluded in previous MRI studies in this area, played an important role in accurate differentiation of positive and negative lymph nodes.
The researchers acknowledged that the basic sequences employed in the study balanced image quality and protocol length, pointing out that patients with suspect findings are referred for additional procedures, including axillary surgery, minimally invasive biopsy or dedicated axillary MRI.
Although the study did not include mediastinal lymph node assessment, the protocol would apply if warranted, they added.
Finally, Baltzer suggested several areas for future research: validation of results in a larger study population, which could provide data to correlate axillary tumor load with imaging results, and a systematic investigation of the impact of MRM on the axillary surgical approach.