Intraoperative 3D-SPECT of sentinel nodes in combination with navigated lymph node biopsy in early oral squamous cell carcinoma

Occult metastasis of the lymph nodes of the neck occurs in up to 20-40 % of all oral squamos cell carcinoma (OSCC). Elective neck dissection of levels I - III is still recommended even in a clinically unsuspicious lymph node staging of the neck (cN0), regardless of the size of the primary tumor. Sentinel lymph node biopsy is not a common standard in the therapy of the primary stage of OSCC (cT1-2, cN0). Even if the method is not yet evidence based, several studies have already shown good results that suggest that the SLNB is an alternative procedure for the standard elective neck dissection in these cases. These studies also showed difficulties in the practical performance of the SLNB. Reasons for this were the close relationship between the sentinel lymph nodes to each other and to the primary tumor. Furthermore, the specific SLNs were difficult to find intraoperatively in a complex soft tissue anatomy of the neck. A new system for SLNB now offers the chance for an intraoperative 3D-SPECT of the radioactive SLNs with a 3D visualization of these structures. The marked SLNs are therefore superimposed on a live image of the patient's neck. This method should enable the surgeon to identify the SLNs more accurately. For a secure resection of these nodes, an additional computer navigated γ-probe is used as well. This navigation allows for the determination of direction and distance from the probe tip to the radioactive focus (SLN). After tumor and SLNs resection, a detection of the remaining radioactive tissue with a final 3D-SEPCT scan is also possible. Remaining lymph nodes can be visualized and resected before the completion of the operation. Even though this method offers promising possibilities in intraoperative visualization and soft tissue navigation, the procedure showed deficits in clinical use. The intra-OP 3D-SEPCT proved itself to be a time-consuming process in practice. The navigation within the soft tissue of the neck in order to find the SLNs proved itself to be imprecise. Possible reasons for this might be inaccurate registration and the soft tissue. The SLNs could often be detected properly only by the use of the acoustic feedback of the γ-probe. For this reason, this expensive and time-consuming procedure has to be evaluated critically from a clinical point of view. This method showed the greatest advantage in intraoperative 3D-SPECT scanning in order to evaluate the complete removal of all radioactive structures (SLNs and tumor) before completing the operation. Parole chiave: sentinel lymphnode, intraoperative navigation, computer assisted surgery, augmented reality