Koos Boeve

78 Chapter 4 per different prior treatment are given in Supplementary data 2. Some SLNs were found in earlier dissected neck levels. For example, eight of the 13 patients with a history of a selective supraomohyoid neck dissection had SLNs located in level I-III, also three of the seven patients with a history of a MRND had SLNs located in level II-IV (Supplementary data 2). If we restrict the drainage pattern analysis to patients with a history of treatment of the ipsilateral neck, unexpected drainage patterns were found in 12 (35%) of the 34 patients and no drainage to any side of the neck was found in 5 patients (12%). DISCUSSION This study demonstrates that SLNB in a previously treated neck can be performed with a high accuracy (sensitivity 75%, NPV 98%). In this study unexpected lymphatic drainage patterns were found in 30% of the patients and no drainage was found in 12% of the patients. SLNB in early stage OSCC has been frequently described in literature during the last decade with high sensitivity rates and negative predictive values [4]. SLNB was initially implemented in our institutions for patients with primary OSCC without previous treatment of the neck. However, after gaining more experience with SLNB, this staging technique was also extended to patients with a previously treated neck [5]. As a result of the previous treatment, lymphatic drainage patterns could be disrupted resulting in aberrant drainage patterns compared to primary OSCC. Lack of knowledge about these aberrant drainage patterns resulted in missing a standard neck staging and standard elective neck dissection in previously treated patients. Flach et al. showed in a study of 22 patients that the SLNB could be useful in previously treated patients with a high sensitivity and negative predictive value for neck staging and especially for assessment of the individual lymphatic drainage patterns after previous treatment [5]. As mentioned in the introduction, only one feasibility study and the above mentioned study of Flach et al. are published for SLNB in patients with a pretreated neck [5,9]. However, interesting studies in a variety of tumour types have been published regarding SLNB in recurrent or second primary tumours. In a recent meta-analysis of aberrant lymphatic drainage in recurrent breast cancer an 59.6% intraoperatively SLN identification rate was found [10]. The authors concluded that SLNB in these patients avoided unnecessary axillary lymph node dissection and provide targeted localized surgery [10]. Similarly, in recurrent vulvar cancer the SLNB procedure seemed feasible, although the authors stated that the