Substernal Goiter: Type II Posterior Mediastinal Goiters

  • Most surgical and radiographic series suggest that substernal goiters affect:
    • The anterior mediastinum in approximately 85% of patients:
      • Extension into the anterior mediastinum brings the thyroid:
        • Anterior to the subclavian and innominate vessels and anterior to the RLN
      • The relationship of the anterior mediastinal goiter to the RLN is as in the normal cervical gland:
        • That is, that the nerve is deep
    • The posterior mediastinum in approximately 15% of patients:
      • When substernal goiter expands to the posterior mediastinum:
        • It excavates the region posterior to the trachea, pushing the trachea anteriorly and splaying the great vessels anteriorly:
          • The thyroid then comes to rest in a space posterior to the innominate vein, carotid sheath contents, innominate and subclavian arteries, RLN, and inferior thyroid artery
      • Of importance, the relationship of the thyroid gland and the RLN is reversed as compared with the normal cervical orthotopic gland-RLN relationship:
        • The RLN is ventral to the inferior component of the thyroid and, if not recognized early on, can be stretched or cut by even the most meticulous thyroid surgeon
        • The nerve can also be entrapped between components of the posterior mediastinal goiter; even in these circumstances, a portion of the goiter will be deep to the RLN:
          • Such posterior mediastinal goiters can come to rest in a space bounded inferiorly by the azygous vein, posteriorly by the vertebral column, laterally by the first rib, medially by the trachea and esophagus, and anteriorly by the carotid sheath, subclavian and innominate vessels, superior vena cava, and phrenic and recurrent laryngeal nerves
  • Posterior mediastinal goiter (type IIA):
    • Can occur ipsilateral to the cervical thyroid gland of origin or may come to rest through retrotracheal extension in the contralateral thorax (substernal goiter type IIB)
  • Extension to the right thorax is more commonly seen as a result of:
    • Aortic arch and associated branch vessels obstructing the left posterior mediastinal descent pathway
  • Contralateral thoracic extension in the posterior mediastinum may occur either:
    • Behind the trachea and esophagus (IIB1) or between trachea and esophagus (IIB2)
  • Axial CT scanning and barium swallow help to determine this pattern
  • Generally the right chest caudal extension:
    • Is limited at the level of the azygous arch

#Arrangoiz #HeadandNeckSurgeon #ThyroidSurgeon #ThyroidExpert #MultinodularGoiter #SubsternalGoiter #CASO #CenterforAdvancedSurgicalOncology

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