Background: For invasive breast cancer, sentinel lymph node (SLN) detection and biopsy at time of surgery are essential for treatment planning. Currently there are at least three FDA-approved methods utilized for sentinel lymph node detection, including radiotracer, dye (most often blue), and the more novel superparamagnetic iron oxide (SPIO). All three are injected prior to surgery and are respectively identified with gamma probe, visual inspection, and magnetic probe. Several advantages of SPIO include injection in the operating room immediately prior to surgery, absence of radioactivity, and detection in lymph nodes for up to 27 days. While radiologists are familiar with radiotracer and dye, SPIO is more rarely used but has important imaging ramifications, including long-term susceptibility artifact on breast magnetic resonance imaging (MRI), limiting interpretation, and sometimes rendering it nondiagnostic. Radiologists must be cognizant of its appearance and limitations.
Learning Objectives: 1. Introduce this relatively novel sentinel lymph node detection method, which was approved by the FDA in 2018. 2. Describe the advantages and disadvantages of SPIO relative to other sentinel lymph node detection methods. 3. Demonstrate the susceptibility artifact associated with SPIO and its limitations on breast MRI. 4. Consider ways to minimize artifact and/or detect recurrent cancers in patients who have received SPIO.
Abstract Content/Results: Here we will review indications for SLN biopsy, methods for SLN detection and limitations/advantages of each method. Cases from our institution will be presented showing SPIO artifact and how to distinguish from other causes. Two cases from our institution will be juxtaposed, as they both involve significant susceptibility artifact with subsequent detection of recurrent cancer obscured by SPIO artifact in one case.
Conclusion: Post breast conservation surgery with SPIO for SLN detection, mammography remains the test of choice for evaluating the lumpectomy bed. SPIO may cause MRI susceptibility artifact, seen on all MR sequences within the lumpectomy bed, limiting evaluation. Thus, it is imperative for radiologists to recognize SPIO MRI susceptibility artifact and understand that it may obscure recurrent cancer.
