Sentinel lymph node biopsy (SLNB) has proven to reliably stage the clinically negative neck in early-stage oral squamous cell carcinoma (OSCC). The 10%-rule, used to define sentinel lymph nodes (SLN) intraoperatively, states that an SLN is defined by gamma counts that are at least 10% of the hottest harvested lymph node (LN). However, this intraoperative rule has not yet been adequately evaluated for early-stage OSCC. This study aims to evaluate the 10%-rule intraoperatively and explore possibilities for redefining this criterion. A single center retrospective study was performed between 2014 and 2023. Patients (n = 66) with clinically node-negative OSCC (cT1-3N0) and positive SLNB were included in this study. Radioactivity of all harvested LNs were measured ex-vivo. Metastatic LNs were assessed for complying with the 10 %-rule. The accuracy of alternative thresholds was evaluated. If multiple positive SLNs on one side of the neck were found, the hottest positive SLN on that side was considered the LN accountable for upstaging the corresponding neck side from N0 to N+. A total of 233 LNs were harvested, of which 98 contained metastases and 190 met the 10%-rule. Of these metastatic LNs, 70 were accountable for upstaging the side of the neck. The 10%-rule correctly staged 69 of 70 metastatic sides of the neck. By increasing the intraoperative cut-off point to 20%, 68 of 70 metastatic sides of the neck were correctly staged and 18 LNs (172 vs. 190) were not defined as SLN. Applying the 10%-rule to each side of the neck increased detection of one metastatic LN. However, this LN was not accountable for upstaging that side of the neck. The 10%-rule in SLNB applies to patients with OSCC and effectively identifies metastatic SLNs intraoperatively. Applying the 10%-rule per neck side must be considered. Increasing the threshold percentage is not advisable.

This study evaluated sentinel lymph node (SLN) identification with CT lymphography (CTL) following peritumoral administration of Lipiodol^® relative to conventional ^99mTc-nanocolloid lymphoscintigraphy (including SPECT/CT) in 10 early-stage oral cancer patients undergoing SLN biopsy. Patients first underwent early dynamic and static scintigraphy after peritumoral administration of ^99mTc-nanocolloid. Subsequently, Lipiodol^® was administered at the same injection sites, followed by fluoroscopy and CT acquisition. Finally, late scintigraphy and SPECT/CT were conducted, enabling the fusion of late CTL and SPECT imaging. The next day, designated SLNs were harvested, radiographically examined for Lipiodol^® uptake and histopathologically assessed. Corresponding images of CT, ^99mTc-nanocolloid lymphoscintigraphy and SPECT/late CTL fusion were evaluated. ^99mTc-nanocolloid lymphoscintigraphy identified 21 SLNs, of which 7 were identified with CTL (33%). CTL identified no additional SLNs and failed to identify any SLNs in four patients (40%). Out of six histopathologically positive SLNs, two were identified by CTL (33%). Radiographic examination confirmed Lipiodol^® uptake in seven harvested SLNs (24%), of which five were depicted by CTL. CTL using Lipiodol^® reached a sensitivity of 50% and a negative predictive value (NPV) of 75% (median follow-up: 12.3 months). These results suggest that CTL using Lipiodol^® is not a reliable technique for SLN mapping in early-stage oral cancer.

Objectives: To assess the efficacy of magnetic resonance (MR) lymphography with gadobutrol contrast for sentinel lymph node (SLN) mapping in early-stage oral squamous cell carcinoma (OSCC). Methods: This pilot study compared the identification of SLNs by MR lymphography using a gadolinium-based contrast agent (gadobutrol) to conventional [^99mTc]Tc-nanocolloid lymphoscintigraphy (including single-photon emission computed tomography/computed tomography (SPECT/CT)) in 10 early-stage OSCC patients undergoing SLN biopsy. The patients initially underwent conventional lymphoscintigraphy following the peritumoral administration of indocyanine green [^99mTc]Tc-nanocolloid (120 megabecquerel; ~0.5 mL). Subsequently, 0.5–1.0 mL gadobutrol was peritumorally injected, and MR imaging was acquired for 30 min. The following day, the identified SLNs were harvested and subjected to a histopathological assessment. The MR lymphography and [^99mTc]Tc-nanocolloid lymphoscintigraphy results were evaluated and compared with respect to those of the SLN identification. The reference standard consisted of a histopathological evaluation of the harvested SLNs, complementary neck dissection specimens, and follow-up data. Results: The MR lymphography detected 16 out of 27 SLNs identified by [^99mTc]Tc-nanocolloid lymphoscintigraphy, revealing an additional SLN that did not harbor metastasis. MR lymphography failed to identify any SLNs in one patient. Of the seven histopathologically positive SLNs detected by [^99mTc]Tc-nanocolloid lymphoscintigraphy, three were identified by MR lymphography. All patients remained disease-free after a median follow-up of 16 months. Compared to [^99mTc]Tc-nanocolloid lymphoscintigraphy, MR lymphography using gadobutrol achieved an SLN identification rate of 59%, a sensitivity of 75%, and a negative predictive value of 86%. Conclusions: MR lymphography using gadobutrol demonstrates limited reliability for SLN mapping in early-stage OSCC.