Koos Boeve

182 Chapter 9 were found for five (12%) patients with a history of radiotherapy. Unexpected drainage (no drainage to ipsilateral levels I-III) was found in 30% of the cases to ipsilateral levels IV and V or to contralateral levels. The altered drainage patterns as a result of the previous neck treatment limit neck staging in cN0 patients with a neck history: which levels needs an END or clinical examination in case of a watchful waiting strategy? Moreover, extensive surgery (neck dissection) in an earlier treated neck is unfavourable because the previous treatment most likely induced fibrosis in the neck. For that reason, the SLNB procedure is currently the most optimal technique for neck staging in previously treated early stage OSCC patients with a clinically negative neck and recommended in the surgical guidelines of the SLNB consensus meeting in 2018 [16]. For a long time, lymphatic drainage of maxillary tumours was thought to be to the para- or retropharyngeal located lymph nodes [46]. Moreover, a lower incidence of lymph node metastases compared to other oral cavity tumours was assumed [46]. In chapter 5 [41], we have shown that SLNs of patients with maxillary tumours are mainly located in cervical neck levels I-III. However, in 2 out of 10 patients drainage patterns to parapharyngeally located lymph nodes were also detected. In 2016, an overview of the literature on the incidence of lymph node involvement in maxillary tumours from patients with an END neck staging or with a regional recurrence was published [47]. In eight studies reported from 2001 till 2013, an incidence rate of 14% to 38% including all stages of maxillary OSCC was reported [47], which is not lower than that of other oral cavity locations, as was assumed before [46]. Another study reported a similar incidence (14%) but mentioned especially the high rate (46%) of contralateral metastases in cN0 maxillary OSCC patients [48]. Remarkably, none of these ten studies [48-57] on metastases of maxillary OSCC, mentioned lymph node involvement of para- or retropharyngeally located lymph nodes. A review from 2019 analysed the involvement of retropharyngeally located lymph nodes in head and neck cancer [58]. Of all 32 included studies, chapter 5 [41] was the only included study that used the SLNB procedure to analyse lymphatic drainage patterns to retropharyngeally located lymph nodes in head and neck cancer [58]. Four of the 32 studies [59-61] reported about retropharyngeal lymph node involvement in OSCC. Incidence rates of 1% [60] and 7% [59] were reported for retropharyngeal metastases, which were most seen in, but were not restricted to maxillary OSCC. One study analysed the two-year disease specific (DSS) and diseases free (DFS) survival and reported a dramatically lower survival for patients diagnosed with retropharyngeal metastases during follow-up compared to patients diagnosed with retropharyngeal metastases at initial treatment, respectively 20% versus 13% for DSS and 24% versus 10% for DFS [60]. Taken together, this current knowledge of maxillary OSCC (incidence, bilateral drainage, retropharyngeal drainage, impact on survival and the assessment of individual drainage