- Thyroid gland lies deep to the sternothyroid muscle and sternohyoid muscle.
- Thyroid gland is located anteriorly in the neck at the level of C5 – T1 vertebrae.
- Thyroid gland consists of right and left lobes connected by “Isthmus”.
- Right and left lobes are located anterolateral to the larynx and trachea.
- Isthmus is located over the trachea usually anterior to the second and third tracheal ring
- Thyroid Gland is surrounded by a thin fibrous capsule.
- Thyroid Gland has a dense connective tissue which connects the capsule to the cricoid cartilage and to the superior tracheal ring.
- External to the capsule there is a loose sheath formed by the pretracheal layer of deep cervical fascia.
VASCULAR SUPPLY :
- Superior thyroid artery
- Inferior thyroid artery
- Thyroid Gland is highly vascular and is supplied by Superior thyroid Artery and Inferior thyroid artery which lies between the capsule and the pretracheal layer.
- Superior thyroid artery descends to the superior poles of the thyroid gland, pierces the pretracheal layer and divides into anterior and posterior branches to supply anteriosuperior part of the gland.
- Inferior thyroid artery is the largest branch of the thyrocervical trunk, it runs superiomedially posterior to the carotid sheath and reaches the posterior aspect of the thyroid gland.
- They divide into several branches and pierces the pretracheal layer and supply the posterioinferior aspect of the gland and inferior poles of the thyroid gland.
- The right and left superior thyroid artery and inferior thyroid artery anastamose with each other with i the gland.
- Superior thyroid vein
- Middle thyroid vein
- Inferior thyroid vein+
- Thyroid Gland is drained by 3 pairs of veins from the thyroid plexus of veins on the anterior surface of the gland anterior to the trachea.
- Superior thyroid veins accompanies superior thyroid artery and drain the superior poles
- Middle thyroid vein courses parallel to the inferior thyroid artery and drains the middle of the lobes.
- Inferior thyroid vein drains the inferior poles.
- Superior thyroid veins and middle thyroid vein drains into inferior juglar vein
- Inferior thyroid vein drains into brachiocephalic veins
LYMPHATIC DRAINAGE :
- The lymphatic vessels of the thyroid gland run in the interlobular connective tissue, they communicate with the capsular network of lymphatic vessels.
- From the capsular network they pass first to the prelaryngeal lymphnodes, pretracheal lymph nodes and paratracheal lymphnodes whic in turn drains into superior deep cervical lymph nodes and inferior deep cervical lymph nodes.
- Laterally, lymphatic vessels located along the superior thyroid vein pass directly to the inferior deep cervical lymph nodes.
- some of the lymphatic vessels may drain into brachiocephaliclymph nodes or thoracic duct
These are derived from Superior cervical sympathetic ganglion, middle cervical sympathetic ganglion, inferior cervical sympathetic ganglion.. they reach the gland through superior thyroid periarterial plexuses and inferior thyroid periarterial plexuses that accompany the thyroid arteries.