title: Thyroid cancer invasion of neck structures: epidemiology, evaluation, staging and management.
abstract: OBJECTIVE
  This review addresses the issue of direct extra-capsular invasion of thyroid cancer; this may occur in several ways and to varying degrees. The evidence regarding the prognostic and treatment implications of extra-thyroidal spread is examined. The phenomenon is most common in papillary carcinoma of the thyroid and that is the focus for this review. Less common, but more aggressive tumours (medullary and anaplastic carcinoma) are not considered here.
  
  
  RESULTS
  Overall, around 15% of thyroid cancers exhibit extra-thyroid spread but the rate is much higher in specific subgroups. The presence of invasive disease affects the staging of the tumour, and the implications for surgery can be substantial if complete tumour extirpation is to be achieved. No particular examination is completely accurate in detecting extra-thyroid spread preoperatively. Invasion posteriorly carries greater morbidity and mortality than anterior spread. The presence of extra-thyroid spread usually warrants adjuvant radiotherapy (radioiodine or external beam).
  
  
  CONCLUSIONS
  Histologic assessment is the gold standard for detecting invasive thyroid cancer. Thyroidectomy is effectively a staging procedure by which the presence and extent of invasive disease can be established and subsequent management determined. Extra-thyroidal spread influences morbidity and mortality.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Manukau City, Auckland, New Zealand. RPMorton@middlemore.co.nz
authors.forename: Randall P
authors.initials: RP
authors.lastname: Morton
authors.forename: Zahoor
authors.initials: Z
authors.lastname: Ahmad
mesh_terms: D003952:Diagnostic Imaging; D004938:Esophageal Neoplasms / Q000473:pathology; D006801:Humans; D007817:Laryngeal Cartilages; D009334:Neck Muscles; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D011379:Prognosis; D012009:Recurrent Laryngeal Nerve; D013964:Thyroid Neoplasms / Q000453:epidemiology / Q000473:pathology* / Q000628:therapy