Anatomy of the Thyroid Gland

Location of Carotid Sheaths

Carotid Sheaths run deep to the investing fascia. They are located anterolaterally in the neck either side of the thyroid gland

Investing Fascia

Encloses all other neck fascial compartment and two pairs of muscles - Trapezius - Sternocleidomastoid

When does the Thyroid Gland reach its final position

Gland reaches its final position in relation to the larynx/trachea in the 7th week of development

Location of parathyroid glands

On the posterior surfaces of the thyroid gland's lateral lobes

General result of recurrent larygneal nerve injury

Paralysis of the vocal cord

How does the thyroid gland migrate?

The thyroid gland migrate inferiorly whilst remaining attached to the tongue via the thyroglossal duct Thyroglossal duct cysts or ectopic thyroid tissue can be located at any position in migratory path

Where does the thyroid gland begin development

- The Thyroid Gland begins development as a midline epithelial proliferation at the junction between the anterior 2/3rd (oral/horizontal part) and the posterior 1/3rd (oropharyngeal/vertical part) of the tongue (foramen caecum in adult)

What does the thyroid gland consits of?

- Two lateral lobes (right and left) - An isthmus- a narrow connecting band

Thyroidectomy Incision

- A collar incision is made within a natural skin crease or in the direction of Langer's Lines - Incision should be just superior to the clavicles & jugular notch (optimal aesthetics with scar hidden by clothing and reduced risk of keloid formation) - The incision is made through skin & platysma

Bilateral Recurrent laryngeal nerve injury results in

- Aphonia (inability to produce sound) - Inability to close the rima glottis (opening between vocal cords) to prevent aspiration (inhalation of foreign body in the lungs) - Inability to produce a good cough (requires closure of the rima glottis)

Vagus Nerve (CN X) route in the Abdomen

- Both vagus nerves pass through the diaphragm with the oesophagus - Then divide into their terminal branches on the surface of the stomach -The terminal branches supply the abdominal organs with parasympathetic axons to the distal midgut

Vagus Nerve (CN X) route in the Neck

- Branch from the Medulla oblongata - Exit the skull via the jugular foramen - Descend through in carotid sheath

Unilateral recurrent laryngeal nerve injury results in

- Hoarseness or weakness of the voice - A weak Cough

Prevertebral (deep) fascia

- Located posteriorly - Made up of - Postural Neck Muscles - Cervical Vertebrae

Tracheal Lymph Nodes

- Pretracheal Node -Paratracheal Nodes

Facial Compartments of the Neck

- Prevertebral (deep) fascia - Investing fascia - Carotid sheaths (x2) - Pretracheal Fascia

Names of Parathyroid Glands

- Right Superior - Left Superior - Right Inferior - Left Inferior

Route of the Anterior Jugular Vein

- Runs within the superficial fascia - Drains into the external jugular vein

Attachments of the Sternocleidomastoid

- Sternal Head: Attaches to the manubrium of the sternum - Clavicular Head: Attaches to the medial end of the clavicle Both heads pass superiorly to attach to the mastoid process of the temporal bone

Pyramidal Lobe of thyroid gland

-Commonly originates from the left lateral lobe - Most attach superiorly to thyroid cartilage - 9.2% are not connected to the main thyroid gland - May extend as far superiorly as the hyoid bone - 44.6% prevalence

What is enclosed within the carotid sheath?

-Internal Jugular Vein - Common arteries - Common internal carotid arteries - Vagus Nerves - Deep cervical lymph nodes

The 4th aortic arch artery is the embryological origin of

-Right Subclavian artery and the arch of the aorta

Route of the External Jugular Vein

-Runs within the superficial fascia -Drains into the subclavian vein

Muscles Supplied by the Spinal Accessory Nerve (CNX1)

-Sternocleidomastoid -Trapezius

Where does the Isthmus lie?

Anterior to the 2nd & 3rd cartilages of the trachea

Attachments of Carotid Sheaths

Attach Superiorly - base of the skull (around the jugular foramen & enterance to carotid canal) Blend inferiorly with the mediastinal fascia

Carotid Sheaths are

Bilateral tubes of deep fascia

Nerve Supply to Platysma Muscle

Cranial Nerve VII (facial nerve)

How will a lump on the thyroid gland or a goitre move

It will move superiorly then inferiorly with the larynx during swallowing

Pretracheal Fascia

Located Anteriorly Enlcoses - Oesophagus - Trachae - Thyroid gland - Strap Muscles - Recurrent Laryngeal nerves

Carotid Sheaths (X2)

Located anterolaterally Enclose - Vagus Nerves - Deep Cervical lymph nodes - Carotid Arteries - Internal Jugular Vein

Platysmus

Platysmus is a skeletal muscle in the superficial fascia of the neck

Function of the Recurrent Laryngeal Nerve

Provides somatic motor supply to most of the skeletal muscles that move the right vocal cord (the intrinsic muscles of the larynx)

Vagus Nerve (CN X) route in the Thorax

Right CNX- Lateral to trachea Left CNX- Left side of aortic arch Both- posterior to the lung hilum and on the oesophagus

What group of muscles does the platysmus belong to

The muscle of fascial expression

Where do the lobes of the thyroid attach?

To lateral aspects of the thyroid &cricoid cartilages and to the trachea