Anatomy Atlas

Thyroid gland

Glandula thyroidea
OrganHigh-yielddraftEndo

Butterfly-shaped endocrine gland wrapped around the upper trachea at C5–T1. It moves with swallowing, lies next to the recurrent laryngeal nerves and parathyroids, and thyroid nodules are a common workup.

Core anatomy

Location

Anterior neck, deep to the infrahyoid (strap) muscles, at about C5–T1; the isthmus lies over the 2nd–3rd (or 2nd–4th) tracheal rings.

Parts
  • Right and left lobes on the sides of the larynx and trachea
  • Isthmus over the upper tracheal rings
  • Pyramidal lobe (variable) rising from the isthmus — remnant of the thyroglossal duct
  • Enclosed in the pretracheal layer of deep cervical fascia, which attaches it to the larynx, so it moves up on swallowing
  • Follicular cells (T3/T4) and parafollicular C cells (calcitonin)
Relations

Posteromedially: the recurrent laryngeal nerve in the tracheoesophageal groove, close to the inferior thyroid artery. Posteriorly: the parathyroid glands. The external laryngeal nerve runs near the superior thyroid vessels. Posterolaterally: the carotid sheath (common and internal carotid arteries, internal jugular vein, vagus).

Arterial supply

Superior thyroid artery (first branch of the external carotid artery) and inferior thyroid artery (from the thyrocervical trunk of the subclavian); occasionally a thyroid ima artery from the brachiocephalic trunk or arch.

Venous drainage

Superior and middle thyroid veins → internal jugular vein; inferior thyroid veins → brachiocephalic veins.

Lymphatic drainage

Prelaryngeal (Delphian), pretracheal and paratracheal (central compartment, level VI) nodes, then deep cervical nodes (see cervical lymph nodes).

Innervation

Sympathetic fibers from the cervical ganglia (vasomotor); secretion is controlled hormonally by TSH.

Notes

Develops from the foramen cecum of the tongue and descends along the thyroglossal duct; persistence gives a thyroglossal duct cyst.

Forms a boundary of

Found in

Mentioned in

Generated automatically from links in other entries.

Course of the recurrent laryngeal nervesAnterior view of the neck and upper chest, patient's right on the left. Each vagus nerve descends beside the common carotid artery. The right recurrent laryngeal nerve leaves the right vagus in the root of the neck and hooks under the right subclavian artery. The left recurrent laryngeal nerve leaves the left vagus in the thorax and hooks under the aortic arch, just lateral to the ligamentum arteriosum, so it is longer. Both ascend in the groove between the trachea and oesophagus, pass close to the inferior thyroid arteries behind the thyroid gland, and enter the larynx to supply all its intrinsic muscles except cricothyroid. The superior laryngeal nerve leaves the vagus high in the neck: its internal branch is sensory above the vocal folds and its external branch supplies cricothyroid.Right vagusInternal laryngeal n.External laryngeal n. → cricothyroidCommon carotid arteryInferior thyroid arteryRight subclavian arteryRight RLN (under subclavian)Tracheoesophageal grooveLarynx (thyroid cartilage)Thyroid glandTracheaLeft vagusLeft RLN (under the arch)Ligamentum arteriosumAortic archPulmonary trunkPatient's right ←→ Patient's leftDashed = behind the thyroid

Swipe sideways to see the whole diagram →

Course of the recurrent laryngeal nerves. Anterior view, patient's right on your left. The right RLN hooks under the right subclavian artery in the root of the neck; the left hooks under the aortic arch beside the ligamentum arteriosum, so it is longer and runs in the chest. Both climb in the tracheoesophageal groove past the inferior thyroid arteries to supply every intrinsic laryngeal muscle except cricothyroid (external laryngeal nerve). Hoarseness after thyroidectomy, or from a lung cancer or aortic aneurysm on the left, points to the RLN.
Original schematic, created for this atlas.
Anterior dissection of the neck with the strap muscles retracted, showing the thyroid gland, superior thyroid artery, middle and inferior thyroid veins, internal jugular veins, common carotid arteries and the left brachiocephalic (innominate) vein
The thyroid gland with its veins and the carotid sheath.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 562. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Cross-section of the neck at C6 showing the layers of deep cervical fascia around the trachea, esophagus, thyroid gland, the carotid sheath (common carotid artery, internal jugular vein, vagus nerve), the prevertebral muscles, sternocleidomastoid and trapezius
Cross-section at C6: the thyroid in the pretracheal fascia beside the trachea and esophagus.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 384. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Thyroid nodule PANCE

Mechanism / lesion

Very common; most are benign (colloid nodules, adenomas); about 5–10% are malignant (papillary carcinoma most common). verify

Classic presentation

Workup: TSH first. Low TSH → radioactive iodine uptake scan (a "hot" nodule is rarely malignant). Normal or high TSH → ultrasound → fine-needle aspiration based on size and suspicious features (microcalcifications, hypoechoic, irregular margins, taller-than-wide).

Thyroid cancer PANCE

Mechanism / lesion

Papillary (most common; radiation exposure; psammoma bodies; lymphatic spread), follicular (hematogenous spread), medullary (C cells; calcitonin; MEN 2), anaplastic (elderly; rapidly fatal).

Classic presentation

A hard, fixed nodule, cervical lymphadenopathy, hoarseness (nerve invasion), rapid growth.

Thyroglossal duct cyst PANCE

Mechanism / lesion

Persistent thyroglossal duct remnant.

Classic presentation

Midline neck mass near the hyoid that moves up with tongue protrusion and swallowing; can become infected. Excise with the middle of the hyoid (Sistrunk procedure) after confirming normal thyroid tissue elsewhere.

Goiter and thyroidectomy complications PANCE

Mechanism / lesion

Goiter — iodine deficiency, Graves disease, multinodular goiter, Hashimoto thyroiditis. Complications of thyroidectomy — recurrent laryngeal nerve injury, hypoparathyroidism, neck hematoma.

Classic presentation

Neck hematoma after thyroidectomy can compress the airway — open the wound at the bedside. Hypocalcemia (perioral tingling, Chvostek and Trousseau signs) from parathyroid injury. Hoarseness from RLN injury. A large goiter can cause Pemberton sign (facial plethora on raising the arms).

High-yield PANCE pearls

  • Thyroid nodule → TSH first; low → uptake scan; normal/high → ultrasound ± FNA.
  • Papillary = most common, psammoma bodies, radiation; medullary = calcitonin, MEN 2.
  • Midline mass that moves with tongue protrusion → thyroglossal duct cyst.
  • Post-thyroidectomy: hoarseness (RLN), hypocalcemia (parathyroids), hematoma (airway).

Imaging anatomy

X-ray

Tracheal deviation from a large goiter may be seen on a chest X-ray.

CT

Retrosternal goiter extent, airway compression, and staging of advanced cancer (avoid iodinated contrast before planned radioiodine therapy when possible).

Ultrasound

First-line imaging for nodules and goiter; guides FNA.

Key views & landmarks
  • Thyroid ultrasound
  • Radioactive iodine (I-123) uptake scan

Physical exam

Surface landmarks

Find the thyroid cartilage, then the cricoid; the isthmus lies just below the cricoid and the lobes lie lateral to it, behind the sternocleidomastoids.

Palpation

Examine from behind or in front with the neck slightly flexed; have the patient swallow water — the thyroid rises. Assess size, consistency, nodules, tenderness (subacute thyroiditis) and cervical nodes. Auscultate for a bruit (Graves disease).

Strength / function testing

Look for signs of hypo- or hyperthyroidism (reflexes, tremor, skin, eyes).

Self-quiz

Q1.

A 42-year-old woman has a 2-cm thyroid nodule. TSH is normal. What is the most appropriate next step?

Show answer

B

With a normal TSH, the next step is a thyroid ultrasound to characterize the nodule and decide on FNA. An uptake scan is for a low TSH.

Q2.

A 7-year-old has a painless midline neck mass at the level of the hyoid that rises when she sticks out her tongue. What is the most likely diagnosis?

Show answer

B

A midline mass that moves with tongue protrusion is a thyroglossal duct cyst, attached to the hyoid and foramen cecum. A branchial cleft cyst lies laterally, along the anterior border of sternocleidomastoid.

Q3.

Six hours after thyroidectomy, a patient has an expanding neck swelling, stridor and difficulty breathing. What is the most appropriate immediate action?

Show answer

C

An expanding post-thyroidectomy hematoma compresses the airway; open the wound immediately (skin and strap sutures) to relieve pressure, then return to the OR. Imaging would delay life-saving treatment.

Q4.

A patient with a thyroid nodule has a low TSH. What is the most appropriate next step?

Show answer

B

With a low TSH, a radioactive iodine uptake scan is next; a "hot" (hyperfunctioning) nodule is rarely malignant. With a normal or high TSH, ultrasound ± FNA is next.

Q5.

Medullary thyroid carcinoma arises from which cells, and which tumor marker is used?

Show answer

E

Medullary carcinoma arises from parafollicular C cells, secretes calcitonin, and is associated with MEN 2. Papillary carcinoma (most common) arises from follicular cells.

Flashcards

See also