Lymph Node Metastasis in Papillary Thyroid Carcinoma (PTC)

  • Lymph node involvement in PTC:
    • The incidence of nodal metastases in adults depends upon the extent of surgery:
      • Among patients who undergo a modified radical neck dissection:
        • Up to 80% have lymph node metastases:
          • Half of which are microscopic
      • Among patients with papillary micro-carcinomas who have prophylactic central node dissection:
        • Microscopic metastases have been reported in 37% to 64%
    • At diagnosis, clinically detectable regional lymph node metastases:
      • Are more common in children (approximately 50%) than adults (30% to 40%)
  • Invasion of either the thyroid capsule or a lymph node capsule into surrounding soft tissue:
    • Has been reported in 5% to 35% of surgical specimens
  • Vascular invasion is seen in only:
    • Approximately 5% to 10%
  • Distant metastases:
    • From 2% to 10% of patients have metastases beyond the neck at the time of diagnosis:
      • Among such patients:
        • Two-thirds have pulmonary
        • One-fourth have skeletal metastases
        • Rarer sites of metastasis are:
          • The brain, kidneys, liver, and adrenals
  • Growth pattern:
    • The growth pattern and biologic behavior of papillary thyroid cancers are variable:
      • At one end of the spectrum is the common:
        • Micro-carcinoma (formerly called occult papillary thyroid cancer):
          • Defined as a tumor equal or less than 1 cm in diameter
          • These micro-carcinomas are found in 15% to 30% of thyroid glands at autopsy
          • This high frequency, coupled with the rarity of clinically detected papillary cancer:
            • Suggests that the presence of a single focus of micro-carcinoma in a thyroidectomy specimen is likely to be an incidental finding of no clinical importance
      • At the other end of the spectrum is a large, locally invasive cancer with distant metastases noted at the time of diagnosis:
        • These tumors are also far more likely than micro-carcinoma to metastasize through intra-thyroidal lymphatic channels and form multifocal tumors or involve regional lymph nodes
  • References:
    • The prognostic significance of nodal metastases from papillary thyroid carcinoma can be stratified based on the size and number of metastatic lymph nodes, as well as the presence of extranodal extension. AU Randolph GW, Duh QY, Heller KS, Livolsi VA, Mandel SJ, Steward DL, Tufano RP, Tuttle For The American Thyroid Association Surgical Affairs Committee’s Taskforce On Thyroid Cancer Nodal Surgery RM SO Thyroid. 2012;22(11):1144

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