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Thyroid gland

The thyroid gland is a bilobed endocrine organ located in the anterior neck, spanning from the C5 to T1 vertebral levels. It lies anterior and lateral to the trachea, connected by a thin isthmus that crosses the second and third tracheal rings. Each lobe is conical, with the apex pointing upward toward the thyroid cartilage and the base lying near the thoracic inlet. The gland is enclosed by the pretracheal fascia and overlies the larynx and trachea. Functionally, it produces thyroid hormones (T3, T4) regulating metabolism, and calcitonin for calcium homeostasis.

Synonyms

  • Glandula thyroidea

  • Cervical thyroid

  • Endocrine thyroid gland

Function

  • Secretes thyroxine (T4) and triiodothyronine (T3) to regulate metabolic rate and growth

  • Produces calcitonin for calcium homeostasis

  • Plays a central role in energy regulation, thermogenesis, and development

Arterial Supply

  • Superior thyroid artery (branch of external carotid artery)

  • Inferior thyroid artery (branch of thyrocervical trunk from subclavian artery)

  • Occasionally, thyroid ima artery (arises from brachiocephalic trunk or aortic arch)

Venous Drainage

  • Superior thyroid vein → internal jugular vein

  • Middle thyroid vein → internal jugular vein

  • Inferior thyroid veins → brachiocephalic veins

  • Provides communication with the venous plexus of the neck and thorax

Nerve Supply

  • Parasympathetic fibers: from the vagus nerve (CN X)

  • Sympathetic fibers: from the cervical sympathetic ganglia (vasomotor only, no secretomotor)

  • Function of hormone secretion is regulated by pituitary TSH, not directly by nerve supply

MRI Appearance

T1-weighted images:

  • Thyroid tissue shows intermediate to slightly high signal intensity relative to muscle, due to iodine content and vascularity

  • Surrounding fat is hyperintense, clearly outlining the gland

T2-weighted images:

  • Normal thyroid appears intermediate to slightly hyperintense relative to muscle

  • Pathology (e.g., thyroiditis, nodules, cysts) appears as heterogeneous hyperintense areas

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, improving visualization of thyroid edema, inflammation, or infiltrative disease

  • Normal gland is intermediate signal, while inflamed or tumorous tissue appears hyperintense

T1 Post-Contrast (Gadolinium-enhanced):

  • Thyroid gland enhances intensely and homogeneously due to rich vascular supply

  • Pathology such as nodules, carcinoma, or thyroiditis appears as heterogeneous or focal enhancement

CT Appearance

Non-contrast CT:

  • Thyroid gland is a soft tissue density structure located anterolateral to the trachea

  • Intrinsic iodine makes it slightly higher density than muscle

  • Nodules, calcifications, or goiters are well visualized

Contrast-enhanced CT (CECT):

  • Thyroid enhances intensely and homogeneously due to vascularity

  • Useful for detecting nodules, thyroid carcinoma, retrosternal goiter, or tracheal compression

  • CTA delineates relationship to carotid arteries, jugular veins, and trachea

MRI images

Thyroid gland coronal MRI image -img-00000-00000

MRI images

Thyroid gland

CT image

Thyroid gland CT axial image-img-00000-00000