Endocrine (inc Head and Neck) Flashcards
What are the branches of facial nerve and what do they supply?
- temporal (frontal part of occiptofrontalis)
- zygomatic (orbicularis occuli)
- buccal (buccinator and upper lip)
- marginal mandibular (lower lip)
- cervical (platysma)
How can you locate the facial nerve during surgery?
The facial nerve’s main trunk emerges from the stylomastoid foramen and winds lateral to the styloid process just above the tendon of the stylohyoid muscle.
- Thus the relationship of the stylomastoid foramen and the tympanomastoid fissure can be used as an operative landmark.
- The main trunk of the facial nerve is less than 1 cm deep to the tympanomastoid suture line at the level of the digastric muscle.
Also can use tragal cartilage which ends in a ‘pointer’. This points to the facial nerve, 1 cm medially and inferiorly
What does greater auricular nerve supply?
C2/3 nerve root
Emerges at midpoint of SCM and travels upwards behind EJV
Has 2 branches – anterior and posterior
- Anterior branch = supplies skin over the parotid/ear lobe
- Posterior branch = supplies retroauricular skin
What forms the retromandibular vein?
The superficial temporal and maxillary veins join within the gland to form the retromandibular vein.
deep to this vein is the external carotid artery
Which nerve is at most risk during submandibular surgery and what are the consequences of damaging this nerve?
- The nerve most at risk is the marginal mandibular branch of the facial nerve.
- It travels anteriorly parallel to the body of the mandible, often running below its lower border (but within 3 cm of it), superficial to the submandibular gland.
- Injury results in the inability to depress the corner of the mouth, which is particularly evident when smiling.
How many lobes does the submandibular salivary gland have, and what structure distinguishes them?
The submandibular gland has two lobes – superficial and deep – which are demarcated by the posterior border of the mylohyoid muscle.
What are the boundaries of the digastric triangle?
- anterior - anterior belly of digastric
- posterior - posterior belly of digastric
- laterally - mandible
- floor - mylohyoid and hypoglossus muscles
- roof - skin, platysma and investing layer of cervical fascia
The submandibular gland is located in this triangle.
which nerve is at risk when ligating the submandibular duct (Wharton’s duct) and what are the consequences?
- the lingual nerve is at risk (branch of the mandibular division of the trigeminal nerve)
- emerges at the medial side of the duct
- consequences = loss of sensation to anterior 2/3rds of tongue
What structures need to be divided an preserved during submandibular surgery?
Structures to divide
- Facial vein (twice)
- Facial artery (twice)
- Submental vessels
- Submandibular ganglion
Structures to preserve
- Mandibular nerve
- Cervical nerve
- Lingual nerve
- Hypoglossal nerve
What are some key steps to avoid injury to important structures during submandibular surgery?
Incision
- transverse skin crease incision placed 2 fingerbreadths (4 cm) below mandible in order to avoid lowermost branches of facial nerve (mandibular and cervical).
- These are easily injured if a more superficial upper flap is raised.
Ligation
- The lingual nerve lies deep to the mylohyoid muscle, and above the deep part of the gland emerging at the medial side of the duct.
- During ligation of the submandibular duct care must be taken to identify the lingual nerve so that it is not damaged at this point.
Dissection
- limited (inferio-posterior) traction on submandibular gland in order to avoid tenting the lingual nerve down in a U-shape.
- Inflammation of the gland itself can make it difficult to separate/identify lingual nerve clearly.
describe the embryology and position of the parathyroid glands?
Parathyroid tissue arises from the interaction of neural crest cells and third and fourth branchial pouch endoderm.
Superior
- arise from the fourth pharyngeal pouch.
- migrate in with lateral anlagen of thyroid which goes onto form Tubercle of Zuckerkandl
- less distance to travel so more constant in location
- usually (80%) located supero-lateral to intersection of the RLN and ITA.
Inferior
- arise from the third pharyngeal pouch.
- Travel with thymus
- variable location but commonly (46%) behind inferior thyroid pole
what are the locations for ectopic parathyroid?
Superior
- posterior to junction of RLN and inferior thyroid artery
- retropharyngeal
- retrolaryngeal
- retro-oesophageal
- posterior mediastinum (very rare).
Inferior
- thyrothymic ligament
- thymus
- superior mediastinum — if the inferior glands fail to separate from the thymus
- rarely they are located within the thyroid gland itself.
What will you do if you cannot find a superior parathyroid gland?
- individual ligation of the superior pole vessels (also helps protect the ESLN)
- complete mobilization of upper pole
- divide ligament of Berry
- If still missing look within the common carotid sheath and along the vagus nerve.
what will you do if you cannot find an inferior parathyroid gland?
- look in thyrothymic ligament and thymus
- These extend from lower thyroid pole into anterior mediastinum
- steronotomy not undertaken at 1st operation as procedures described often remove sufficient parathyroid tissue to overcome hypercalcemia
What is the arterial supply to the adrenals?
- superior adrenal artery = from inferior phrenic
- middle adrenal artery = from aorta
- inferior adrenal artery = from left renal
