Patients
Patients with a final diagnosis of WDTC who were treated at the Tel-Aviv ‘Sourasky’ Medical Center between January 1st 2006 and December 31st 2015 were identified from the institutional electronic database. Demographic, clinical, pathologic, and radiologic data on all included patients were extracted. Inclusion criteria were all patients diagnosed with WDTC and confirmed ETE as described in the operative and pathological reports. All patients had undergone surgery that included at least a total thyroidectomy as a first procedure, or a subsequent completion thyroidectomy. The tracheal invasion group included only patients diagnosed with invasion stage I and II according to Shin et al.[14]. All patients in the tracheal invasion group had undergone a shave resection of the trachea. Patients with other forms of ETE (e.g., strap muscles, RLN, esophagus, larynx, and subcutaneous soft tissue) that had undergone a thyroidectomy with excision of all gross extra-thyroidal disease were included in the non-tracheal invasion group. Patients were excluded from the study for the following reasons: insufficient preoperative investigational measures (that included at least a neck ultrasound and a fine-needle aspiration), pathologies other than WDTC , undergoing surgical procedures that did not include at least a total t or completion thyroidectomy, partial resections of gross disease with residual macroscopic disease (R2 resection), minimal ETE (e.g. focal ETE detected only on histological examination), ETE invading only peri-thyroidal fat [15], or tracheal resection procedures (window or full circumferential resection).