SLNBx in head and neck cancer is becoming accepted as useful in predicting the cervical nodal status for clinically node negative neck. However, the application of SLNBx in clinical settings requires several problems to be overcome, including proving the technical feasibility of the procedure used at each institute (which varies between institutions) and achieving an acceptable identification rate of the sentinel node and acceptable predictability for cervical nodal status (4
In the first two cases in our series, we used a combination of blue dye mapping and radiotracer injection. However, we experienced difficulty in determining the precise location of the blue-stained nodes before skin incision when using the blue dye technique, resulting in unnecessary dissection (4
). Moreover, the rate of identification and the prediction rate of neck lymph node pathology of sentinel nodes has been reported to be only 50-75%, making it difficult to accurately select all first draining lymph nodes (4
) and the passage time of blue dye is relatively too short (about 15 min) to allow the procedure to be completed (4
). For these reasons, the blue dye mapping technique was not used after the second cases in our series.
In contrast, radiolocalization of the sentinel lymph node is gaining popularity (11
). In recent studies using radiotracers, the diagnostic accuracy and the localization rate reaches almost 100% (9
). The figures obtained from this study correspond with other reports. At identifying the sentinel nodes in node-negative oral cavity cancer patients, the detection rate ranged from 93.8% to 100% (3
) in the literature, which is similar to that of our method. Also the diagnostic accuracy of predicting cervical nodal status by analyzing the sentinel lymph nodes in our study (100%) confirms the high predictability of earlier studies (94-100%) (7
One problem occurs when the lymphatic bed being surveyed is immediately adjacent to the primary lesion containing injected radionuclide. To avoid this problem, we first excised the primary tumor with an adequate safety margin before identifing sentinel nodes using a hand-held gamma probe, which was easily achieved due to the absence of radioactivity interference from the injected site.
There are several 99m
Tc labeled radiocolloids reported in the literature, but as the materials licensed for use in Korea are limited, 99m
Tc filered tin colloid was selected for this study. 99m
Tc tin colloids were filtered into its relatively regular particle size (≤200 nm), because smaller particle colloids tend to be faster moving, and in case of disease present within the sentinel node, larger particles are less likely to penetrate into the sentinel node, so have a chance not to detect it (8
). A literature also reported that smaller sized 99m
Tc tin colloids were slightly superior to the regular sized 99m
Tc tin colloids in the identification of sentinel nodes (97.3% vs. 86.5%) (12
). We found that 99m
Tc filtered tin colloid is an alternative radiotracer that produces reliable results.
The assistance of a qualified nuclear medicine physician was essential for the handling of the radioisotope and for interpretation of the lymphoscintigraphic imaging. In this study, we gave some modifications to the injection time and the amount of radiotracer.
On the day prior to surgery, the tracer was injected around the primary tumor, instead of in the morning on the day of surgery. The amount of 99m
Tc filtered tin colloid radiotracer in this study was 5-6 mCi in contrast to that of other reports (1-2 mCi) (3
). With its half-life of about 6 hr, 1-1.5 mCi of radiotracer remained in the tissue on the following morning, which is similar to several other reports. Our modifications of a delay of 12-20 hr between the injection of 99m
Tc filtered tin colloid and the application of SLNBx have a major advantage in giving sufficient time to get more static images, which effectively identified the sentinel lymph node during lymphoscintigraphy and intraoperative gamma probing in all patients.
As discussed by Byers et al., another concern in SLNBx is whether this technique will detect 'skip metastasis' with acceptable identification rate (14
). Recently, the concept of 'skip metastasis' is being redefined as skip metastasis may represent non-standard but sequential or multiple drainages of an individual neck in parallel array (9
). According to this explanation, the sentinel node will always be the initial site of micrometastasis, and the evaluation of the histological status of the sentinel node may help to predict the incidence of regional micrometastasis in head and neck squamous cell carcinoma.
If a reliable assessment of the sentinel lymph nodes could be made with frozen section biopsy, a decision regarding elective neck dissection would be possibly made at the time of SLNBx and unnecessary surgeries could be avoided with safe oncological results. Frozen section analysis may be a rate-limiting step for SLNBx as the determining factor in concurrent elective neck dissection. We believe that the data regarding frozen sectioning should be added to the ongoing study.
Recent meta-analysis across the world reported that the SLNBx procedure has shown high sensitivity rates for oral squamous cell carcinomas and is reliable and reproducible (16
), which we also reconfirmed through this study by the validation of our technique. Now, SLNBx procedure seems to be sufficiently validated, though it requires further refinement of intra-operative frozen section analysis (18
). Trial of SLNBx procedure as a sole method for neck management also showed a promising result with a high diagnostic accuracy (83.3%), which could spare unnecessary neck dissection in patients with no evidence of metastasis in the sentinel lymph nodes (19
). Through subsequent clinical trials, the authors think that the SLNBx procedure can achieve its position firmly as a useful and effective method for clinically node negative oral cancer.
In conclusion, our techniques of lymphoscintigraphy and SLNBx using 99mTc filtered tin colloid in squamous cell carcinomas of the oral cavity were technically feasible and identified the sentinel node in all cases. The histological evaluation of sentinel nodes according to our protocol provided the exact reflections of cervical nodal status. This study could guide as the primary protocol of SLNBx procedure for clinical trials if the results of further study corroborate the data presented here.