SPIO-enhanced MRI for sentinel lymph node mapping in oral cancer: a prospective feasibility study

Background Patients with early-stage node-negative oral cancer undergo a sentinel lymph node biopsy (SLNB) or elective neck dissection under general anesthesia. A noninvasive imaging alternative would be of great interest. Superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance imaging (MRI) can visualize draining lymph nodes and potentially metastases. We investigated the optimal combination of SPIO injection and T2*-weighted MRI settings to identify the sentinel lymph nodes (SLNs), the lymphatic drainage pattern, and possibly to detect metastatic SLNs. Materials and methods SPIO nanoparticles were injected submucosally around the primary tongue tumor in ten patients after routine SLNB imaging with indocyanine green-[ 99m Tc]Tc-nanocolloid, and MRI was performed 1 h after injection. SPIO dose was adjusted for every two patients based on the imaging quality. Drainage patterns were compared between single-photon emission computed tomography (SPECT)/computed tomography (CT) and MRI. MRI appearance of SLNs was compared to histopathology of resected nodes. Results One mg of iron was deemed a suitable dose after two dose alterations. All 25 SLNs observed on SPECT/CT in eight patients were also identified on MRI. Including higher echelons, 55 lymph nodes were seen on SPECT/CT, while 107 lymph nodes were seen on MRI. Eighteen lymph nodes showed a mixture of partial MRI signal attenuation and retention, which, when compared to histopathology, made discrimination between metastatic and nonmetastatic lymph nodes solely based on MRI impossible. Conclusion SPIO-enhanced T2*-weighted MRI is suitable for mapping SLNs and lymphatic drainage pattern, showing significantly more lymph nodes compared to SPECT/CT. Discriminating metastatic from nonmetastatic nodes does not seem feasible after SPIO injection. Trial registration Clinicaltrials.gov NCT04803331. Registered 4 March 2021; https://clinicaltrials.gov/study/NCT04803331 . Relevance statement SPIO-enhanced MRI seems noninferior to the current method of SLN detection with technetium, with better anatomical detail than SPECT/CT: if proven comparable, SPIO-enhanced MRI could be considered a nonradioactive alternative with higher spatial resolution to define lymphatic drainage of tumors. Key Points The use of superparamagnetic iron oxide (SPIO)-enhanced MRI in head and neck cancer is underassessed. SPIO-enhanced MRI detects nodal drainage patterns comparably to SPECT/CT. SPIO-enhanced MRI does not discriminate lymph node metastases from false positives.