Goiter

The term goiter refers to:
- An abnormal growth of the thyroid gland
Depending on the etiology goiters can be:
- Diffuse
- Nodular
May be associated with:
- Normal thyroid hormone production
- Decreased thyroid hormone production
- Increased thyroid hormone production
The clinical manifestations vary with:
- Thyroid function and with the size and location of the goiter
Anatomical Relationships:
- In healthy adults without iodine deficiency:
  - A normal thyroid gland is approximately:
    - 4.0 cm to 4.8 cm x 1.0 cm to 1.8 cm x 0.8 cm to 1.6 cm in size
  - Mean sonographic volume of:
    - 7 mL to 10 mL:
      - Thyroid volume measured by ultrasonography:
        Is slightly greater in men than women
        Increases with age and body weight
        Decreases with increasing iodine intake
Weight of the thyroid gland:
- 10 grams to 20 grams:
  - As high as 30 grams is considered normal
The normal thyroid gland:
- Is immediately caudal to the larynx and encircles the anterolateral portion of the trachea
The thyroid gland is bordered by:
- The trachea and esophagus posteriorly
- The carotid sheath laterally
Enlarging thyroid lobes:
- Usually grow outward:
  - Because of their location in the anterior neck in front of the trachea:
    - Covered only by the thin strap muscles, subcutaneous tissue, and skin
- As a result of this outward growth:
  - Even very large goiters:
    - May not compress the trachea or impinge on the great vessels lateral to the lobes:
      - However, in patients with substantial enlargement of one lobe or asymmetric enlargement of both lobes:
        The trachea, esophagus, or blood vessels:
        May be displaced or, less often, compressed
      - Bilateral lobar enlargement:
        Especially if the goiter extends posterior to the trachea:
        May cause either:
        Compression or concentric narrowing of the trachea
        Compression of the esophagus
        Compression of the jugular veins
The thoracic inlet:
- Is an ovoid area that measures approximately 5 cm x 10 cm:
  - Boundaries:
    - The sternum anteriorly
    - The first thoracic vertebral body posteriorly
    - The first ribs laterally
- The inlet is traversed by the:
  - Trachea
  - Esophagus
  - Blood vessels
  - Nerves
- The inferior pole of each thyroid lobe:
  - Normally lies above the thoracic inlet:
    - However, with some goiters, there is growth of one or both lobes through the inlet into the thoracic cavity:
      - Which can result in obstruction of any of the structures in the inlet:
        Such goiters are called substernal:
        Although retrosternal is probably a more precise term
Most substernal goiters are in the:
- Anterolateral mediastinum:
  - But approximately 10%:
    - Are located primarily in the posterior mediastinum
The prevalence of substernal goiter as a percentage of thyroidectomies:
- Ranges from 2% to 19%