Thyroid Diseases

Published on 16/04/2015 by admin

Filed under Surgery

Last modified 22/04/2025

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2 Thyroid Diseases

Thyroid and Parathyroid Anatomy

image

Thyroid Gland and Pharynx: Posterior View

Thyroid

• Thyroid typically consists of right and left lobes, connected by a midline isthmus, with an ascending pyramidal lobe in about 50% of cases.
• Location

image Immediately anterior and lateral to trachea, from about 5th cervical vertebra to 1st thoracic vertebra
image Medial to internal jugular veins
image Anterior to common carotid arteries
image Deep to infrahyoid muscles: sternohyoid (medial), omohyoid, sternothyroid (lateral)
image Infrahyoid muscles embedded in pretracheal fascia, deep to investing fascia of neck (superficial layer of deep fascia)

• Connective tissue (true) capsule is continuous with the septa dividing the stroma of the gland.
• Surgical (false) capsule lies external to the true capsule and is derived from the pretracheal fascia.
• Of the overlying strap muscles, the sternohyoid is most superficial, overlying the sternothyroid and thyrohyoid.
• Thyroid follicular (epithelial/principal) cells secrete thyroxine (T4) and triiodothyronine (T3), regulated by TSH receptors.
• Thyrotropin-releasing factor or hormone (TRF or TRH) from hypothalamus controls TSH release from pituitary.
• Parafollicular (C) cells secrete calcitonin.

Parathyroids

• Superior parathyroid glands usually lie between the true capsule of the thyroid and its investing surgical (false) capsule fascia.
• Inferior parathyroid glands might lie between the true and false capsules, within the thyroid parenchyma, or on the outer surface of the surgical capsule.

Vessels and Lymphatics

image

Blood Vessels and Parathyroid Glands

Arterial Supply

• Superior thyroid arteries arise bilaterally from the external carotid arteries at, above, or below the bifurcation of the common carotid.
• Inferior thyroid arteries arise bilaterally from the thyrocervical trunks (branches of the subclavians) or occasionally directly from the subclavian arteries.
• Thyroid ima artery (1% of patients)

image Variable, unpaired, anterior to trachea
image Supplies isthmus
image Can arise from brachiocephalic, right common carotid, or aortic arch: important consideration in tracheostomy

Venous Drainage

• Thyroid vein plexus is in the substance of the gland and on its surface.
• Thyroid plexus is drained by 3 main pairs of veins.

image Superior thyroid veins: accompany superior thyroid arteries
image Middle thyroid veins: occasionally double or absent, arise posterolaterally, drain independently
image Inferior thyroid veins: largest, drain inferiorly

Lymphatic Drainage

• Vessels in interlobular connective tissue parallel the arterial supply
• Communicate with capsular network
• Drainage into prelaryngeal, pretracheal, paratracheal nodes, then into superior and inferior deep cervical nodes
• Lateral drainage directly into inferior deep cervical nodes
• Some drainage into brachiocephalic nodes, trunks, or thoracic duct

Clinical Correlates

Thyroidectomy

• Partial or total removal of the thyroid may be indicated for refractory severe hyperthyroidism, Graves’ disease, nodules, or cancer.
• Recurrent laryngeal nerves are at risk during surgery.
image

Graves’ Disease: Thyroid and Ocular Pathology

Recurrent Laryngeal Nerve

• Nerve ascends from the thoracic outlet, in or near the tracheoesophageal groove.
• Course past the inferior thyroid artery is highly variable: it can pass anterior, between, or posterior to the artery’s bifurcation into anterior and posterior branches.

Thyroid Cancer

• Rare, but most common endocrine malignancy in the United States

Types of Thyroid Cancer

• Thyroid adenomas
• Follicular adenomas
• Papillary thyroid carcinoma

image Most common thyroid carcinoma
image Predominantly in women
image Slow growing

• Follicular thyroid carcinoma

image 10% of all U.S. cases
image Predominantly in women
image Slow growing
image Hürtle cell carcinoma considered a variant
image 1/3 of cases with radiation exposure history, no other common factors

• Medullary thyroid carcinoma

image Can be associated with multiple endocrine neoplasia, usually as the first manifestation
image Arises from parafollicular C cells

• Malignant lymphoma of the thyroid

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2 Thyroid Diseases

Thyroid and Parathyroid Anatomy

image

Thyroid Gland and Pharynx: Posterior View

Thyroid

• Thyroid typically consists of right and left lobes, connected by a midline isthmus, with an ascending pyramidal lobe in about 50% of cases.
• Location

image Immediately anterior and lateral to trachea, from about 5th cervical vertebra to 1st thoracic vertebra
image Medial to internal jugular veins
image Anterior to common carotid arteries
image Deep to infrahyoid muscles: sternohyoid (medial), omohyoid, sternothyroid (lateral)
image Infrahyoid muscles embedded in pretracheal fascia, deep to investing fascia of neck (superficial layer of deep fascia)

• Connective tissue (true) capsule is continuous with the septa dividing the stroma of the gland.
• Surgical (false) capsule lies external to the true capsule and is derived from the pretracheal fascia.
• Of the overlying strap muscles, the sternohyoid is most superficial, overlying the sternothyroid and thyrohyoid.
• Thyroid follicular (epithelial/principal) cells secrete thyroxine (T4) and triiodothyronine (T3), regulated by TSH receptors.
• Thyrotropin-releasing factor or hormone (TRF or TRH) from hypothalamus controls TSH release from pituitary.
• Parafollicular (C) cells secrete calcitonin.

Parathyroids

• Superior parathyroid glands usually lie between the true capsule of the thyroid and its investing surgical (false) capsule fascia.
• Inferior parathyroid glands might lie between the true and false capsules, within the thyroid parenchyma, or on the outer surface of the surgical capsule.

Vessels and Lymphatics

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