Koos Boeve

77 SLNB in oral cancer after previous neck treatment ipsilateral neck without a history of pretreatment and in the ipsilateral neck with a history of chemoradiation therapy. In the first two patients, no additional metastases were detected after harvesting respectively 21 and 17 lymph nodes in the completed neck dissection specimens. Because of the history of chemoradiation and the metastasis size (ITC), the last patient received watchful waiting instead of a neck dissection. These 3 patients did not show regional disease during follow-up. One patient (2%) was diagnosed with regional recurrence without local disease in level II at the ipsilateral side of the neck after 7 months of follow-up. This patient had a second primary tumour located in the buccal mucosa and only negative SLNs were found in level I at the contralateral side. This patient was previously treated with a MRND at the ipsilateral side of the neck for the first primary tumour, followed by postoperative chemoradiation at both sides of the neck. This patient was still alive after 19 months of follow-up after the regional recurrence was surgically removed and postoperatively irradiated. One regional recurrence resulted in a 75% sensitivity with a 95% CI of 22-98% (3 of 4 true positive) and 98% NPV with a 95% CI of 88-100% (42 of 43 true negative) of the SLNB in patients with a previously treated neck. If we restrict the accuracy analysis to patients with a history of neck dissection and/or radiotherapy in the ipsilateral neck, one out of 34 patients showed a positive SLN and one patient showed regional recurrence after a negative SLNB, resulting in a 50% sensitivity (1 of 2 true positive) with a 95% CI of 3-97% and a NPV of 97% (32 of 33 true negative) with a 95% CI of 82-100%. Lymphatic drainage patterns In 38 of the 43 patients with a second primary or local recurrence at the previously treated neck side SLNsweredetected, resulting inan88% identification rate.The fivepatientswithout detectable SLNs had in common a history of radiotherapy of the neck (Supplementary data 1). Since lymphatic drainage is expected generally in levels I-III for OSCC, in 30% (13/43) patients unexpected drainage was found. Of these 13 patients, four patients showed SLNs located ipsilaterally in level IV as closest located SLN, in two patients this closest location was ipsilaterally in level V. Seven patients had only SLNs located contralateral from the side of the well-lateralized local recurrence or second primary tumour (Supplementary data 1). Besides a lower identification rate, unexpected drainage was more common in patients with a history of neck irradiation compared to patients with a history of a SLNB and comparable to patients with a previous neck dissection, respectively 40% versus 11% and 38%. However the highest unexpected drainage was found after a history of neck dissection combined with postoperative radiotherapy (88%). Localization of harvested SLNs per patient and