Contribution of SLN investigation with 99mTc-nanocolloid in clinical staging of thyroid cancer: technical feasibility

Abstract

It is a matter of controversy whether prophylactic lymph node dissection improves prognosis and survival in papillary thyroid carcinoma (PTC) patients without suspicion of lymph node metastases either clinically or on ultrasonography. It is possible that in such patients the use of lymphatic mapping and sentinel lymph node (SLN) biopsy, as are employed for other tumours, will be of assistance. The aim of this study was to evaluate the feasibility of preoperative 99mTc-nanocolloid lymphoscintigraphy and an intra-operative SLN procedure in the management of PTC patients. Twenty-five consecutive patients were entered in the study between April 2005 and October 2005. All had a preoperative diagnosis of malignancy obtained by fine-needle aspiration cytology (FNAC), without clinical or ultrasonographic evidence of loco-regional lymph node involvement. Patients underwent preoperative lymphoscintigraphy after the injection of 99mTc-nanocolloid [median 6 MBq (range 4-9 MBq) in 0.1-0.2 ml saline injected intratumorally under ultrasound guidance] and an intra-operative SLN procedure using a hand-held gamma probe. Surgery was performed by the same surgeon in all patients. Preoperative lymphoscintigraphy identified at least one SLN in all patients. During surgery, using the gamma probe, the surgeon was able to find at least one SLN in all cases. A good correlation was found between preoperative imaging and probe results. Metastasis was found in at least one SLN in 12 (48%) patients. In seven (28%) patients the involved SLN was the most radioactive SLN, while in five (20%) patients a less radioactive SLN was involved by malignancy. Ten of these 12 patients had only micrometastases (<2 mm). Micrometastases were found in the most radioactive SLN in six cases and in less radioactive SLNs in four cases, while in two patients more lymph nodes visualised at lymphoscintigraphy ipsilateral to the primary tumour were sites of metastasis. The rate of nodal involvement was very high in our series: in 48% of patients at least one metastatic lymph node was found. From a technical point of view the intra-operative SLN procedure in PTC patients was easy to perform, without major intra-operative complications. Our promising preliminary experience needs to be confirmed in larger series of patients series with longer follow-up.