Koos Boeve

64 Chapter 3 False negativity was defined as patients with IRR in an earlier SLNB negative neck side, regardless of a positive SLNB on the other side of the neck. Four (4%) patients in our cohort were diagnosed with IRR in a SLNB negative side of the neck, which is comparable with other studies [6,8]. Retrospectively, the reason for missing these regional metastases remains unclear; shine-through phenomenon and aberrant lymphatic drainage due to metastatic tumour in the SLNs might be involved. Another possible explanation might be micrometastases in lymph nodes, other than the SLN (skip metastases). Other studies reported a lower sensitivity of the SLNB procedure in FOM tumours compared to other oral cavity subsites due to the shine-through phenomenon [7,8,23,24]. One patient in this study had a FOM with an IRR resulting in an 80% sensitivity and a 96% NPV for FOM tumours. Retrospectively, this SLNB was overlooked because of this shine- through phenomenon (Figure 2). To overcome shine-through and subsequent regional recurrences, Stoeckli et al. proposed a surgical technique with dissection of all the LNs in level I irrespective of the location of the SLNs [25]. Van den Berg et al., combined the SLNB procedure with radio- and fluorescence guidance and found this combination especially helpful in detecting SLNs located close to the primary tumour [26]. Our data support the findings of the previously mentioned studies [25,26], that patients with primary tumours adjacent to level I could benefit from additional techniques besides the SLNB procedure alone. The upstaging rate in this study (27%) is in agreement with the literature; 23-37% [1,2,7,8]. We found no additional metastasis in the MRND lymph nodes after a SLNB positive for ITCs or micrometastases. Recently, den Toom et al. reported that the ratio of positive versus negative SLNs and the size of the tumour in the SLN possibly could be predictive factors for non-SLN metastasis in SLN positive patients. However, their analysis was underpowered due to the use of the ITC, micro- and macrometastasis classification in just a few SLNB studies [27]. No additional metastasis in ITC or micrometastasis SLN positive patients, could be the reason why Liu and Wang et al. concluded in their meta-analysis that SSS is not necessary for SLN assessment [15]. Despite the lack of impact of the SSS on the IRR rate, in agreement with den Toom and our data presented in this paper, SLN metastasis size might be used to select patients for routine follow-up instead of MRND [8]. Besides the SSS itself, also the step interval size could be discussed. After the second international conference on SLNB, intervals of 150 µm were recommended [28]. As was reported earlier for breast cancer, Jefferson et al. suggested that SSS intervals of 2 mm are thin enough to detect micrometastasis [29,30]. In this study intervals of 500 µm were used, because our head and neck SCC protocol was adapted from our vulvar SCC SLNB protocol. This is a protocol we have much experience with and has shown to provide accurate staging of vulvar SCC in our centre [31-33]. Besides this, the accuracy we found is comparable to that of most head and