Neck anatomy 2 Flashcards
What are some causes of lumps in the neck?
- Cervical (branchial) cyst (embryological)
- Thyroglossal duct (embryological)
- Thyroid gland (elnargement or tumour)
- Lymphadenopathy (tumour or infection)
- Salivary gland (tumour or infection)
- Epidermoid cysts
What can lymph nodes be grouped into?
Lymph nodes can be grouped into levels I-VI
This guides prognosis and tx in head and neck cancer –> determine lymph node spread of primary head and neck tumours
Number of levels of nodes determined and size of lymph nodes, best mode of tx can be instituted (surgery/ radiotherapy/ chemotherapy). Node level enables prognosis to be made.
What are the levels lymph nodes can be grouped into?
- Level 1 –> from midline submental triangle to level of submandibular gland
- Level 2 –> from skull base to level of hyoid bone anteriorly, and posteriorly to the level of the sternocleidomastoid.
- Level 3 –> inferior to hyoid bone, up to cricooid arch, posterior follows the sternocleidomastoid
- level 4 –> inferior to cricoid to top of manubrium of sternum, anterior to posterior border of sternocleidomastoid
- Level 5 –> posterior to sternocleidomastoid from skull base to clavicle, anterior to trapezius
- Level 6–> below hyoid and above jugular notch of sternum in the midline
- Level 7 –> below level of jugular notch
What do many of the head/ neck structures develop from?
Many develop from series of loops of tissue called the pharyngeal arches.
What is a pharyngeal arch?
Pharyngeal arches = Interconnecting loops of ectoderm, mesoderm and endoderm (lower face and neck)
Outside covered in ectoderm, inside covered in endoderm and inbetween those layers packed with mesoderm –> core of mesenchyme
Where does the mesoderm within a pharyngeal arch come from?
What type of cells are required within a pharyngeal arch?
Mesoderm has to migrate into the pharyngeal arch, if this doesnt occur –> pharyngeal arch defect.
Cranial neural crest-derived mesenchymal cells (ectomesenchyme) migrate into pharyngeal arches, from midbrain and hindbrain region forming:
neurons
Schwann cells
smooth muscle cells
osteoblasts
chondrocytes
how many pharyngeal arches are there in humans?
There are 6, however arch 5 is only transient, in the adult you’re left with only 5 arches: 1, 2,3,4,6
What is a pharyngeal pouch?
What is a pharyngeal cleft/ groove?
Pharyngeal pouch = internal indentation within a pharyngeal arch. Tissue that develops into specific organs may sit here.
Pharyngeal cleft/ groove = external indentation separating the pharyngeal arches
Why are there only 4 pharyngeal arches shown?
Only 4 Pharyngeal arches shown as only arches 1,2,3,4 and 6 develop.
Arch 5 disapppears, arch 6 is small and will appear tucked under arch 4.
What does each arch have?
- Each arch has an aortic arch arterial vessel supplying it (from the heart tube in red within thorax region)
- Mesoderm develops –> muscle, cartilage, cartilage can form bone
- Each is innervated by a cranial nerve
Which cranial nerve supplies pharyngeal arch 1?
Which muscles develop from arch 1?
What bones/ ligaments develop from arch 1?
1st arch –> cranial nerve V supplies it
Muscles of mastication, mylohyoid, anterior belly of digastric, tensor tympani, tensor veli palatini
Bones/ ligaments: Malleus, incus, spine of sphenoid, sphenomandibular ligament, maxilla, zygona and mandible
What signs and sx might be associated with a pharyngeal arch 1 defect?
What cells have failed to migrate?
Small mandible, zygoma and maxilla may not develop properly, leading to eyes being in incorrect position.
Plus conductive deafness –> incus and malleus do not develop properly
Defects in the development of pharyngeal cleft 1 can result in preauricular (i.e. in front of the pinna of the ear) cysts and/or fistulas.
Neural crest cells have failed to migrate.
What aortic arch is associated with arch 2?
What innervates arch 2?
What are the derivatives of arch 2?
- Associated with 2nd aortic arch, develops into stapedial artery
- Innervated by facial nerve CN VII
- Derivatives: Muscle
- muscles of facial expression
- posterior belly of digastric
- stylohyoid muscle
- stapedius
- Derivatives: Bone/ cartilage:
- lesser horn of hyoid
- upper half of body of hyoid
- stapes
- styloid process
What innervates pharyngeal arch 3?
Which aortic arch is it associated with?
- Innervated by CNIX (Glossopharyngeal)
- Associated with aortic arch 3 –> contributes to common carotid and proximal part of internal carotid artery
- Derivatives: Muscle
- stylopharyngeus
- Derivatives: Bone/ cartilage
- greater horn of hyoid
- lower half of body of hyoid
What aortic arch is assocaited with pharyngeal arch 4?
What CN innervates it?
What are the derivatives of arch 4?
- Associated with aortic arch 4 –> contributes to proximal right subclavian and arch of aorta
- innervated by CNX
- derivatives: muscular:
- muscles of soft palate (except tensor veli palatini)
- muscles of pharynx (except stylopharyngeus)
- cricothyroid
- cricopharyngeus
- Derivatives: bone/ cartilage:
- thyroid cartilage
- cricoid cartilage
- arytenoid cartilage
- corniculate cartilage
- cuneiform cartilage
- Note 4th and 6 th arches contribute to laryngeal cartilage
Arch 6 is associated with aortic arch?
Innervated by which cranial nerve?
Derivatives are?
Arch 6 associated with aoritc arch 6, conturbutes to priximal pulmonary artery and ductus arteriosus
innervated by CNX
derivatives: muscular:
intrinsic laryngeal muscles (except cricothyroid)
skeletal muscle of oeosphagus
Derivatives: Bone/ Cartilage:
Thryoid/ cricoid/ arytenoid cartilage/ corniculate/ cuneiform cartilages (plus 4th contributes)
What are pharyngeal pouches?
What do pouches 1-4 develop into?
Pharyngeal pouches are the internal indentations between the arches.
Pouch 1 – >develops into tubotympanic recess (middle ear and pharyngotympanic tube)
Pouch 2 – >develops into palatine tonsil (epithelium lining pouch 2 forms crypt of tonsillar mass)
Pouch 3 – > Inferior parathyroid gland and part of the thymus
Pouch 4 –> superior parathyroid gland (doesnt migrate much inferior migrates lower than it), plus parafollicular C cells (migrate to within the thyroid gland).
What happens to many of the pharyngeal pouch derivatives?
Many of the pharyngeal pouch derivatives migrate inferiorly to reach their final position:
Inferior parathyroid gland migrates down to thryoid
Superior parathryoid gland doesnt migrate much
Parafollicular C cells migrate into the thyroid gland
Thymus has to migrate down into to mediastinum (remember within superior mediastinum in children, eventually migrates to anterior mediastinum in adults).
Why is knowledge of migration patterns of pharyngeal pouch derivatives important clinically?
Useful in the case of abnormal migration and surgical removal, derivatives may not be where you think they will be.
What does the pharyngeal cleft and pouch 1 develop into?
Region formed by pharyngeal cleft and pouch 1 develops into the external and middle ear, and tympanic membrane.
1st cleft develops into your external auditory meatus
1st pouch will develop into the tympanic cavity (houses malleus/ incus/ stapes) and mastoid antrum, pharyngotympanic tube (which connects to the nasopharynx).
Tympanic membrane = Thin tissue between cleft 1 and pouch 1 is formed of ectoderm, endoderm and mesoderm = tympanic membrane
What may a remnant of the 1st pharyngeal cleft be observed as?
Remnants of the 1st pharyngeal cleft may be observed externally as auricular (preauricular) sinuses/ cysts
Right pic = preauricular sinus (first cleft did not fully disappear)
Left pic = auricular/ preauricular cyst
Why do we not have ridged neck / gill remnants?
Due to growth of 2nd arch tissue growing downwards to cover over pharyngeal clefts 2-4
as it does so it seals off the cervical sinus, normally an open space that should disappear.
What does the platysma muscles form within?
What innervates platysma?
Platysma forms within the downgrowth of pharyngeal arch 2 and is innervated by CN VII
What can occur if pharyngeal arch 2 fails to grown over the lower arches/ cover the cervical sinus?
Cervical (branchial) cysts, sinuses or fistulas are formed from remnants of the embryological cervical sinus.
Most of sinus can be obliterated, but some can remain and be quiescent. Then suddenly grow over a period of a few weeks, self contained sac full of cellular debris/ fluid = cervical cyst.
Cervical cysts can appear slowly, but many appear quickly.
Often form on the border of anterior border of sternocleidomastoid in the anterior triangle.
Answer the qu’s on the picture plus what can be done to identify the full extent of pathology here?
- Cervical sinus in both patients hasn’t disappeared as it should. If the cervical sinus remains open it can form a cervical sinus/ fistula that opens and discharges onto the lower neck.
- Insert catheter into the hole within the patients neck (due to unclosed sinus) and introduce contrast into each patient to view the extent of the sinus, or it may be a fistula.
- Sinus effectively will be blind ended, whereas as fistula will join the outside world to a body cavity.
- Note a fistula in the Xray shown.
- Fistulas may open into the palatine tonsil
Where does the thyroid gland begin its development?
where does the tongue develop from and how does this help explain sensory innervation of the tongue?
The thyroid gland begins its development at the posterior aspect of the tongue at the foramen caecum, the tongue begins its development at the top end of the pharyngeal arches.
Thyroid gland its therefore a epithelial endoderm derived structure.
In picture shown, cut down line A-B, looking at the pharyngeal arches from the back:
Tongue develops from swellings on arch 1 and arch 3. Majority of tongue develops from arch 1, innervated by CN V, arch 3 innervated by CN IX
Lingual thyroid –> thyroid gland tissue that hasnt migrated properly
Describe the descent of the thyroid gland
Thyroid gland passes inferiorly through the neck via the thyroglossal duct.
Thryoglossal duct attaches to the hyoid bone, if the bone moves, the duct moves, the thyroid gland moves. Therfore duct moves during swallowing and tongue protrusion.
Hence during thyroid examination you get the patient to swallow and stick their tongue out.
Where in the neck will a thryoglossal duct cyst present?
Will the cyst move on swallowing and tongue protrusion?
Thryoglossal duct cyst can present anywhere in the midline of the neck.
Some may sit above the hyoid, sit within the tongue tissue itself or situated within the anterior neck.
The mass on the neck moves during swallowing or on protrusion of the tongue because of its attachment to the tongue via the tract of thyroid descent.
What is the case in this patient?
Thyroid gland was removed from this patient due to inconclusive MRI.
Be aware the the thyroid gland can migrate to abnormal positions.
Where is the thyroid gland normally located? The isthmus?
Describe the blood supply to the thyroid gland?
The thyroid gland is attached to the larynx and trachea
The isthmus of the thyroid sits over tracheal rings 2-3 at C7 (pyramidal lobe can project superiorly from the isthmus).
Thyroid gland has a rich vascular supply:
1) Superior thyroid artery and vein; artery from external carotid artery, vein to internal jugular vein
2) middle thyroid vein drains to internal jugular vein
3) inferiro thyroid artery and vein; artery from thyrocervical trunk, vein to the left brachiocephalic vein
Why does the thyroid gland move when the larynx moves?
What fascia surrounds this region?
Lateral thyroid ligaments attach the thyroid to the cricoid cartilage, therefore thyroid moves with larynx movement. (pathologies of the thyroid gland will also move with the larynx)
Pretracheal and buccopharyngeal fascia surrounds this region.
What can compress the trachea? How would this present?
The thyroid gland wraps around the lateral sides of the larynx and trachea.
Therefore goitre or tumour may compress the trachea causing a cough/ stridor.
Trachea may also be compressed by enlarged thryoid gland/ or a bleed into the visceral compartment following thyroid surgery.
What is the weak spot at the posterior aspect of the pharynx?
what can form here?
weak spot formed by the change in angle of the muscle fibres, where inferior constrictor muscle meets cricopharyngeus.
Zenker diverticulum/ pharyngeal pouch can form here
Describe the location of the parathyroid glands
There are 4 parathyroid glands in total, located on the posterior surface of the thyroid capsule
Most commonly located with two superior parathyroid glands at level of /cricoid cartilage/cricopharyngeus and inferior parathyroid glands at the inferior pole of the thyroid gland.
However, there can be variation along anywhere along the line of descent.
What can thyroid gland enlargement cause?
How may it present?
- Thyroid gland enlargment can compress the trachea, causing stridor,/ tracheal deviation/ dysponea and/or affect swallowing
- Thyroid gland enlargment can be visible or can occur retrosternally into the mediastinum.
- Note in the xray the trachea is deviated due to enlarged trachea.
What can limit thyroid superior enlargement?
Limited to inferior enlargment due to surrounding by fascia and the strap (infrahyoid muscles)
Green pointer on sternothyroid which particularly limits enlargement.
Label the image and describe the defects associated with pharyngeal arches
- Red –> cervical/ branchial cyst classically sits anterior to sternocleidomastoid
- Yellow –> Cervical (branchial) sinus/ fistula will discharge, normally at front border of sternocleidomastoid. It can extend to the palatine tonsil
- Branchial vestige –> cartialge grew in lower pharyngeal arch, serves no purpose
- Blue –> Thryoglossal duct cyst or ectopic thryoid tissue
- Green –> auricular/ preauricular sinus or cyst
Where do the cutaneous sensory nerves to the neck emerge?
What is this point called clinically and why is it useful?
Cutaneous sensory nerves carrying C2-C4 emerge from the posterior border of the middle 1/3rd of sternocleidomastoid.
This point is called the nerve point of the neck –> a nerve block here anaesthetises the neck skin, may also anaesthetise the phrenic nerve (C3-C5)
Label the image
Red question mark = accesory nerve
What are the roots of the accessory nerve?
What muscles does it supply?
Describe its route?
Accessory nerve routes C1-C5
Supply sternocleidomastoid and trapezius
Exits the skull via jugular foramen within the carotid sheath, emerges under the SCM around 10 cm from mastoid tip, passes deep to trapezius
Where does the hypoglossal nerve pass in the neck?
Hypoglossal nerve passes lateral to the carotid vessels and under the occipital artery.
(therefore vulnerable in carotid endarterectomy or lymph node removal)
Passes into the floor of the mouth deep to mylohyoid.
Describe the route of the glossopharyngeal nerve
CN IX exits skull at jugular foramen, passes inferiorly through the superior neck into the pharynx between the contrictor muscles
Often passes between the carotid vessels and sends a branch to the carotid sinus/ body (feeds back to the cardiovascular centres in the medulla).
How does sympathetic innervation reach the head and face?
Via three sympathetic chain ganglia:
1) superior cervical ganglia (C1-C4)
2) Middle cervical ganglia (C5-C6)
3) Stellate ganglion/ cervicothoracic (C7-C8)
Where does the thoracic duct pass to join the venous sx?
Describe its route
Supraclavicular lymph nodes receive lymph from where?
Thoracic duct passes through the roof of the left neck to enter the left subclavian vein.
It passes posterior to the left common carotid artery and the left internal jugular vein, carries lymph from most of the body except lymph from the right head/neck/ upper limb/ parts of the lungs.
Supraclavicular lymph nodes –> sit around junction of lymphatic ducts and subclavian vein, may enlarge in metastatic upper GI cancer spread
