L20: anatomy of thyroid gland & head and neck cancers

Question 1

Describe the anatomical location of the thyroid gland

Answer 1

Located in the anterior neck & spans the C5-T1 vertebrae
Consists of two lobes which are connected by a central isthmus
Lobes of the thyroid gland are wrapped around the cricoid cartilage & superior rings of the trachea
Gland is located within the visceral compartment of the neck – bounded by pretracheal fascia

Question 2

What is a thyroglossal cyst?

Answer 2

Results from a build-up of secretions within the duct
Typically presents as a midline lump which rises on tongue protrusion
Left untreated -> cyst can become infected & form a cutaneous fistula
Treatment: complete excision

Question 3

Describe the anatomical relations of thyroid gland

Answer 3

Anterior – infrahyoid
Lateral – carotid sheath
Medial – larynx, pharynx, trachea, oesophagus, external laryngeal & recurrent laryngeal nerves

Question 4

Describe the arterial supply to the thyroid gland

Answer 4

1) Superior thyroid artery – first branch of the external carotid artery; close proximity to the external branch of SLN
2) Inferior thyroid artery – arises from the thyrocervical trunk (branch of the subclavian artery); close proximity to the RLN

Question 5

What is the thyroid ima artery? What problems can it cause?

Answer 5

Small proportion of people there is an additional artery – thyroid ima artery
Can arise from the brachiocephalic artery or arch of aorta
Ascend in front of trachea to the isthmus
May prove problematic -> if need access to the trachea for a surgical airway
Source of rapid bleeding & when cut can retract behind the mediastinum so difficult to reach and ligate

Question 6

Describe the venous drainage of the thyroid gland

Answer 6

Superior, middle & inferior thyroid veins form a venous plexus around the thyroid gland
Superior and middle drain into IJV
Inferior drains into the brachiocephalic vein

Question 7

Describe the innervation and lymphatic drainage of the thyroid gland

Answer 7

Innervation: sympathetic trunk

Lymphatic drainage: paratracheal and deep cervical nodes

Question 8

Why does the thyroid gland move up on swallowing?

Answer 8

1) Thyroid gland is ensheathed within the pretracheal fascia which attaches to the hyoid bone. The hyoid bone elevates with swallowing and therefore so will the thyroid gland
2) Posterior surface of the gland is also attached to the cricoid cartilage by connective tissue (Berry’s ligament), as the larynx elevates with swallowing, this too will elevate the thyroid gland

Question 9

List the most common cancers which occur in the head and neck

Answer 9

Oral cavity, larynx & pharynx

Most begin in the squamous mucosal surfaces lining these structures & are predominately squamous cell carcinomas

Question 10

List the main risk factors for head and neck cancers

Answer 10

Heavy alcohol & tobacco use 
Age
Men
Previous EBV infection 
Chewing of betel quid (Paan) 
HPV

Question 11

Describe common clinical manifestations of head and neck cancers

Answer 11

Common initial manifestations – unexplained painful and/or mucosal ulceration or lesion within oral cavity, unexplained hoarseness of voice, dysphagia or odynophagia (painful swallowing)
Otalgia in a normal ear can also be a red flag
Cancers can spread to lymph nodes – cervical lymphadenopathy is a common initial presenting sign

Question 12

Describe clinical diagnosis and staging of head and neck cancers

Answer 12

Through clinical examination, biopsy of lesion and imaging
Endoscopic investigation will be necessary for cancers involving nasal cavity, pharynx & larynx
Staging: TNM
-T = tumour size/location
-N = degree of lymph node involvement
-M = presence or absence of distant metastases

Question 13

Describe the treatment of head and neck cancers

Answer 13

Staging helps determine appropriate treatment for the patient
Early-stage: surgery or radiotherapy
More advanced: surgery and adjuvant chemotherapy
Most types of head and neck cancers – permanent & often significant implications on the anatomical structures essential for eating/drinking, speaking & breathing -> require expert support

Question 14

Describe the cervical plexus

Answer 14

Network of nerve fibres that supplies innervation to some of the structures in the neck and trunk
Located in the posterior triangle of the neck & within the prevertebral layer of cervical fascia
Anterior rami of cervical spinal nerves C1-C4

Question 15

Describe the phrenic nerve

Answer 15

Arises from the anterior rami of C3-C5
Provides motor innervation to the diaphragm
Nerves travels down the surface of the anterior scalene muscle & enters the thorax, descends anteriorly to the root of lung to reach the diaphragm

Question 16

What is the ansa cervicalis?

Answer 16

Loop of nerves, formed by nerve roots C1-C3
Gives off four muscular branches which supply the infrahyoid muscles
Can be found lying anteriorly or in the carotid sheath

Question 17

What is the nerve point of the neck?

Answer 17

All the cutaneous branches of the cervical plexus converge and emerge from around the midpoint on the posterior border of SCM
Cervical plexus nerve block can be used to anaesthetise and block these sensory branches
Inadvertent involvement of the phrenic nerve may happen due to close proximity of this nerve, causing temporary paralysis of hemidiaphragm -> such blocks are avoided in patients with significant respiratory disease