Thyroid Disorders and Anatomy

Thyroid Disorders

• Thyroid disorders are common and can present with a neck swelling or symptoms and signs of thyroid dysfunction (hypo- or hyper-thyroidism).

Thyroid Anatomy

• The thyroid gland consists of two lateral lobes joined by the isthmus, which overlies the 2nd and 3rd tracheal rings.
• The pyramidal lobe is a superior extension near the midline, present in up to 70% of cases.
• Each thyroid lobe is cone-shaped, measuring approximately 5cm in length and 2-3 cm wide in its transverse and anteroposterior dimensions.
• The thyroid gland weighs 15-25g.
• A normal thyroid gland is not palpable, and a visible or palpable thyroid almost always implies some degree of enlargement and pathology.

Thyroid Physiology

• The thyroid gland produces thyroid hormones, primarily triiodothyronine (T3) and thyroxine (T4), which regulate growth and function of many organ systems.
• T3 and T4 are synthesized from iodine and tyrosine.
• The thyroid also produces calcitonin, which plays a role in calcium homeostasis.
• Thyroid hormone output is regulated by thyroid-stimulating hormone (TSH) produced by the anterior pituitary, which is regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus.

Thyroid Enlargement

• Thyroid enlargement can be symmetric (goitre) or asymmetric (solitary nodule).
• A thyroid enlargement can be differentiated from other causes of a cervical mass by its location in the lower midline of the neck and its movement on swallowing.