Detection of the sentinel node using a magnetic tracer in thyroid cancer. A technical pilot study

There is no standard procedure for the detection of the sentinel node (SN) in thyroid disease. However, the recent detection of the SN using a paramagnetic tracer is proving to be useful in breast cancer and melanoma. The objective was to assess the utility of super paramagnetic iron oxide tracer for the intraoperative detection of the SN in patients with papillary thyroid cancer without nodal involvement in the preoperative study.

A single center, prospective pilot study of a class IIa medical device (a paramagnetic tracer). The study included thyroid cancers which were T1-T2 tumors in the cytohistological analysis with a negative preoperative nodal assessment, operated on consecutively during scheduled treatment. For the localization of the SN, an interlesional injection of 2mL of super paramagnetic iron oxide was administered. After ten minutes, ferromagnetic activity was detected in the adjacent nodes. Once the node had been detected, we proceeded by extracting it for intraoperative analysis. The effectiveness of the procedure for detecting the SN was assessed, with the main variable being whether it was detected or not.

The project was assessed after the first cases had been carried out. The SN was located in all cases, which was done easily in the first four, but in the fifth case the SN detection was complicated by the interference of the reusable neurostimulation electrodes with the ferromagnetic signal. Intraoperative histology revealed the SN was positive in 80% (n=4) of cases (20% [n=1] were macrometastases and 60% [n=3] micrometastases). Total thyroidectomies were carried out, with central lymph node dissection in 4 of the patients and lateral in one due to the result of the detected SN. The histology showed the carcinoma was papillary, a classic type, in 80% (n=4) and a follicular variant in 20% (n=1). Forty percent (n=2) were multifocal, 40% (n=2) had vascular infiltration, and 60% (n=3) had extrathyroidal extension. Staging determined the application of radioactive iodine therapy (150mCi) in 80% of cases (n=4).

A paramagnetic tracer can be useful for detecting the SN and correctly staging papillary carcinoma.