Thyroid Surgery Flashcards
What are the main surgical diseases of the thyroid glands?
- Hyperthyroidism
- Mass lesions -> Adenomas (cats) & carcinomas, adenoCs (older dogs)
Describe the anatomy of the thyroid glands?
- Lateral and slightly ventral to 2
nd & 5th tracheal cartilage - rings
- Right more cranial
- Right gland
- carotid artery, internal jugular vein and
vagosympathetic trunk - Left gland
- oesophagus
- Recurrent laryngeal nerves pass dorsal to glands
Where can thyroid ectopic tissue be found?
- along trachea
- thoracic inlet
- Thoracic portion of aorta
What hormones does the thyroid secrete?
- Thyroxin (T4)
- Tri-iodothyroxine (T3)
- Calcitonin - Ca2+ homeostasis
How do these hormones work?
- Controls metabolism
- T4→T3 in tissues
- High in Iodine
What usually causes Feline hyperthyroidism?
- Most common endocrine disorder in middle-aged or older cats
- Bilateral
- Adenoma
- 2% carcinoma
- Adenoma →carcinoma
CS of Feline hyperthyroidism?
- CS: weight loss, polyphagia, polyuria, polydipsia, increased vocalization, agitation, increased activity,
tachypnoea, tachycardia, vomiting, diarrhoea, an unkempt hair coat - +/- palpable goitre
What might we also see in hyperthyroid cats ?
» Concurrent Chronic Renal Insufficiency
* masks chronic kidney disease (CRI)
* once euthyroid, CRI becomes apparent
What options for tx of feline hyperthyroidism?
- Oral medication (thiamazole/carbimazole)
- Transdermal gel
- Iodine Restricted Diet
Describe medical option for hyperthyroidism?
- fast effect (two to four weeks),
- no anaesthesia
- no hospital stay
- Life long medication→£££
- difficulty with administration, daily/twice daily
- side effects, anaemia, neutropenia and facial pruritus
- conversion of a thyroid adenoma (benign) to a thyroid carcinoma (malignant)
Describe transdermal gel ?
- As above but easier to administer
- Difficulty with precise dosing
- Not licensed
What is the gold standard treatement for hyperthyroidism?
Radioactive iodine therapy
Describe radioactive iodine therapy?
- All tissues treated – ectopic
- 1 in 5 have multiple and/or intrathoracic thyroid tissue
- Permanent
- Specialist facility needed
- Human safety concerns
- Traditionally involved long hospital stay in isolation
- Now some centres only hospitalise for five days
- High upfront cost
Make a table with advantages and disadvantages of all tx options for hyperT?
What might be some periop considerations in hyperthyroid cats?
- Cardiomyopathy - tachyC, murmur, HCM -> investigate prior
- CRI -> up to 40% masked -> attempt trial anti-tyroid for weeks prior to more permanent tx
- Hypokalaemia -> in 32% -> parenteral IVFT supplementation
Periop consideraitons of hyperthyroid cats pt2?
- avoid jugular venepuncture prior to surgery
- Send gland for histology
- Recurrence higher with unilateral thyroidectomy
- Positioning super important -> dorsal with neck hyperextended and forelimbs pulled caudally
What is a modified extracapsular thyroidectomy ?
- PReserves cranial thyroid artery
- Lower risk of damage to parathyroid -> low hypoCa rate
- Low recurrence rate
Management of hypoparathyroidism?
Serum Ca2+ measured daily for 4-7 days in bilateral sx
acute hypoparathyroidism management?
- 10% Calcium gluconate IV slowly to effect
- Follow with CRI
- ECG to monitor for bradycardia/arrhythmia
Maintenance of hypoparathyroid tx?
- Oral vitamin D and calcium administration
- calcium lactate
- dihydrotachysterol or calcitriol
- can sometimes be hard to source and expensive
What are some top tips for thyroidectomy?
- If RAI is feasible then best option
- Prep for anaesthetic as best possible
- Consider staged bilat sx
- Send for histo
- Communicate risks clearly
- Can be cheaper tha. medical management
How do canine thyroid tumours usually present?
- commonly in older, large breed dogs -> mass in cervical region
>Compress trachea -> dyspnoea, coughing
>compress oedophagus gagging, dysphagia
>recurrent larungealn dysphonia, dyspnoea
>sympathetic nerve, horner’s
T/F majority of canine thyroid tumours are malignant ?
True > rarely produce excess hormones, most euthyroid
-> most > 3 cm when detected and >85% malignant
Diagnostics for canine tumours?
- Palpation –firmly attached, freely
moveable - Cervical and thoracic rads
- Abdo US
- CT
- Biochem, haem, coagulation, serum
T4 - FNA – often blood contaminated
and non diagnostic - (care with biopsy)
Tx for canine thyroid tumours?
- Surgical removal, if possible
- Removal can be difficult
- Invade local blood vessels; jugular veins & carotid artery, recurrent laryngeal nerve,
trachea, oesophagus- Haemorrhage likely and can require transfusion
- Likely to require suction drain
- Partial surgical debulking, rarely indicated due to risk of haemorrhage
- Radiation or chemotherapy for masses that are non-resectable
PRognosis for thyroid tumour removal?
Guarded -> best of moveable <3cm non metastatic (1-3 yr survival)
Anatomy fo the canine thyroid?
What complications of thyroidectomy might we see?
- Haemorrhage / seroma
- Laryngeal paralysis (nerve damage)
- Hypopararthyroidism -> damage to hyperP BS or parathyroidectomy (hypoCa 2-5 days postop & facial or muscle twitching)
- Incomplete excision/reocurrence (ectopci tissue)
Describe primary hyperparathyroidism?
- Uncommon in dogs, rare in cats
- Parathyroid adenomas (carcinomas reported)
- HyperCa2+, low phos
- PU/PD, vomiting, weakness, constipatio
Diagnosis of primary hyperparathyoridism?
- Imaging rarely helpful
- Serology
- PTH with HyperCa2+ and normal renal function
- Rule out neoplastic causes of hyperCa2+
Tx for primary hyperparathyroidism?
Parathyroidectomy? +/- thyroidectomy
what are some other endocrine surgical procedures to be aware of?
- Adrenelectomy -> for adrenal Tumours not for PDH!
- Hypophysectomy (transsphenoidal) -> removal of pituitary gland in acromegaly cats (70% diabetic remission) or for PD HAC in dogs
Describe Insulinoma?
- Seen most commonly in dogs
- 95% malignant
- Travel to regional lymph nodes
- Low blood glucose causes weakness seizures, ataxia muscle
tremors
What is the Whipples Triad?
- Presence of hypoglycaemic signs (often neuro)
- Fasting blood often less than 2mmol/L
- Releif of clinical signs after glucose admin or feeding
What can we do for insulinoma?
Pancreatectomy
