Endocrine Flashcards
what is the general structure of the thyroid?
paired bilobed gland - right and left glands
where does the thyroid gland typically lie?
caudal to the larynx, between 5th and 8th tracheal rings
where is the thyroid in relation to the trachea?
ventrolateral to the trachea
right gland slightly more cranial than left
why is the thyroid at risk of haemorrhage during surgery?
very well vascularised
why is it important to be aware of iatrogenic damage during surgery on the thyroid?
there are numerous neurological structures in the area which require careful identification during surgery
where can ectopic thyroid tissue be found?
lying in the midline from the tongue to the abdomen
why is is possible to have ectopic thyroid tissue?
as a result of the path the thyroid tissue undergoes during embryonic development
why do we place oesophagostomy tubes on the lhs of the neck?
the oesophagus sits more on the lhs of the neck, in contact with the left thyroid gland
what is a functional thyroid condition?
one which produces thyroid hormones
how can we categorise surgical conditions of the thyroid?
functional vs non-functional
benign vs malignant neoplasia
when benign conditions can affect the thyroid gland?
adenoma
adenomatous hyperplasia
cysts
what malignancies can affect the thyroid gland?
carcinoma
adenocarcinoma
what type of benign thyroid masses affect dogs?
typically small and non-functional - rarely diagnosed
what type of benign thyroid masses affect cats?
typically functional and cause hyperthyroidism
what is the most common type of thyroid mass in cats?
95% of all cases are benign adenoma/adenomatous hyperplasia
are malignant thyroid masses in dogs typically functional?
no - mostly non-functional, do not cause hyperthyroidism and are instead presented due to the mass itself
are thyroid masses often malignant in cats?
no - typically functional, benign masses
do thyroid cysts occur commonly?
no - rare
what are the main pre-operative considerations for thyroidectomy?
body condition score
likelihood of metastasis
cardiovascular effects
renal effects
ocular effects
co-morbidities - typically older animals
degree of medical stabilisation achieved
what are the pre-op cardiovascular considerations for thyroidectomy?
tachycardia
hypertension
what are the pre-op renal considerations for thyroidectomy?
pre-renal azotemia
what are the pre-op ocular considerations for thyroidectomy?
retinal detachment secondary to hypertension
what are the pre-op c-morbidity considerations for thyroidectomy?
CVS, renal, increased GA risk, cachexia, arthritis
what is the benefit of medical stabilisation before thyroidectomy?
improvement of asa status
what is involved in medical stabilisation of hyperthyroidism?
decrease HR with anti-thyroid meds
treat hypertension and stabilise rhythm with atenolol
support renal function - diet, supplements, fluids
try to increase body weight
what are the pre-operative considerations for thyroidectomy in dogs?
BCS - may be reduced due to effects of cancer
metastasis?
co-morbidities present as usually older animals
do dogs require medical stabilisation before thyroidectomy?
not usually needed, usually non-functional so far sew systemic effects
how wide should the clip be for thyroidectomy?
from level of jaw to thoracic inlet lengthways
wide clip - to jugular grooves widthways
what position should the patient be in for thyroidectomy?
dorsal recumbency with sandbag under neck to elevate, keep neck straight
why is it better to do unilateral thyroidectomy if possible?
risk of bilateral surgery much higher
how might the parathyroid gland(s) be salvaged during thyroidectomy?
sometimes reimplantation of the parathyroid tissue into the surgical site will allow for neovascularisation
what is the risk of reimplanting the parathyroid tissue?
risks seeding tumour
what are the surgical options for thyroidectomy?
several techniques for vet to choose from
need to consider whether unilateral/bilateral, esp in regards to removal of parathyroid glands
what are the complications of thyroidectomy which are unrelated to surgical technique?
GA risks - ASA status
unmask CRF if cat and/or a functional mass
hypothyroidism
what are the complications of thyroidectomy which are related to surgical technique and skill?
haemorrhage
seroma formation
laryngeal paralysis
horners syndrome
hypocalcaemia
recurrence of tumour
which thyroidectomy surgeries are at higher risk of haemorrhage?
possible with all, but particularly with canine invasive masses
how can haemorrhage be avoided during thyroidectomy?
careful surgical technique
what affects likelihood of seroma formation after thyroidectomy?
related to size of mass
how can we avoid seroma formation after thyroidectomy?
careful surgical technique
how can horners syndrome develop as a result of thyroidectomy?
damage to sympathetic trunk (rare)
what are the signs of horners syndrome after thyroidectomy?
anisocoria
third eyelid partially across
how can we avoid post-op hypocalcaemia from iatrogenic hypoparathyroidism?
protect the parathyroids by good choice of technique and careful surgical technique
staged procedure - remove one side only (whichever is larger)
consider pre-emptive peri-operative support e.g. pre-op vit D and post-op calcium (both oral)
when is recurrence of a thyroid mass more common?
presence of ectopic tissue
use of an intracapsular technique
with malignant neoplasia
what is important to consider when weighing up medical or surgical management for thyroid masses?
age of patient - will surgery be cheaper than life-long medication if patient is younger
how many parathyroid glands are there in total?
4
name all the parathyroid glands
left extracapsular (cranial)
right extracapsular
left intracapsular (caudal)
right intracapsular
what is the overall role of the parathyroid glands?
increase blood calcium
how are the parathyroid glands arranged?
in 2 sets of pairs
what are the options for medical treatment of primary hyperparathyroidism?
ethanol injection
heat ablation
what is the surgical treatment option for primary hyperparathyroidism?
parathyroidectomy
what is the most important post-op concern after parathyroidectomy?
monitoring for hypocalcaemia
which species more commonly develops primary hyperparathyroidism?
most commonly seen in dogs
what is the prognosis post-op for primary hyperparathyroidism?
usually benign, functional adenoma (95%)
what are the pre-op considerations for parathyroidectomy?
systemic effects of hyperparathyroidism
co-morbidities unrelated to hyperparathyroidism
medical stabilisation
complications
what systemic effects might we see in pre-op parathyroidectomy patients?
hypercalcaemia affects renal function
what might be involved in pre-op medical stabilisation of parathyroidectomy patients?
diuresis with high levels of IVFT to ‘dilute’ the calcium (?)
support renal function, care not to overhydrate
how wide should the clip be for parathyroidectomy?
level of jaw to thoracic inlet
jugular grooves widthways
what approach is used for parathyroidectomy?
ventral midline - px in dorsal recumbency
when might the associated thyroid be removed during parathyroidectomy?
if intracapsular/caudal parathyroid