121. Thyroid_parathyroid Flashcards
(46 cards)
anatomical differences in dog vs cat thyroid glands
2 glandsdogs: communicate w ventral isthmuscats: lack isthmus, lack caudal thyroid artery
components of the carotid sheath
–common carotid artery–internal jugular vein–vagosympathetic trunk
blod supply to thyroid gland
cranial and caudal thyroid arteries (caudal is lacking in cats)cranial thyroid artery is the first branch of common carotid arterycaudal thyroid artery branches from brachiocephalic trunk
number of parathyroid glands
2 on each gland (4 total)1. extra capsular PTG—cranial (blood supply from cranial thyroid artery)2. intra capsular PTG–caudal and embedded(blood supply from vessels surrounding the parenchyma)variations exist
areas where ectopic thyroid tissue can be found
- along trachea2. thoracic inlet3. mediastinal4. thoracic aorta(base of tongue to base of heart)ectopic parathyroid tissue is uncommon in dogs but up to 50% cats
thyroid gland hormones
–requires iodine to produce thyroglobulin (stored in follicles): contains precursors for thyroid hormone synthesis–T4, T3 (lesser extent) released into blood which are larger bound to proteins–T4 major secretory product BUT T3 is the most active form–production of hormones stimulated by TSH release by pituitary/TRH release by hypothalamus
parathyroid gland hormones
–PTH made, stored and secreted by chief cells of PTG–effects are to INCREASE Ca, DECREASE P (direct–bone, renal; indirect–GI)BONE: Ca, P resorption from increased osteoclastic activityRENAL: decrease excretion Ca, increase excretion P; activates vitamin D to calcitriol (1,25 dihydroxycholecalceferol)GI: calcitriol increases Ca and P absorption (INDIRECT)
most physiologic form of calcium in the body
ionized Ca —most active
where is calcitonin from and what is its function?
thyroid gland parafollicular cells (C cells)increases with increase Ca in order to LOWER Ca levelsdecreases bone resorptionNO effect on kidney, GI
most functional thyroid tumors in cats are_____
BENIGN—adenoma, hyperplasia, goiterBILATERAL 70-90%one study said up to 25% could be carcinoma (70% metastatic rate)
prevalence of coexisting renal disease in cats with hyperthyroidism
40%may need pretreatment with methimazole and recheck blood work to see if hyperthyroidism was masking underlying renal disease
percentage of hyperthyroid cats that have hypokalemia
30%
screening test for hyperthyroid cats
–PALPATE (90% have nodule)–total T4–elevated in 90% cats with hyperthyroidism–other tests: free T4, TSH stimulation test, T 3 suppression test–scintigraphy: confirms and localizes (technetium 99m)-not affected by methimazole tx bc radio nucleotide gets trap it is a not a function; will normally highlight thyroid, salivary glands, and gastric mucosa but intensity will be greater in thyroid
considerations for anesthesia of a hyperthyroid cat
–avoid drugs that potentiate tachycardia/arrhythmias (ketamine, atropine)–beta antagonist if needed–supplement K if needed–ensure no previous renal insufficiency (pretreat with methimazole 2-3 weeks before sx)
methods of thyroidectomy
–intracapsular–rate of recurrence is high, but preserves extra capsular PTG–modified intracapsular–extracapsular–no attempt to save PTG (may lead to hypoPTH)–modified extracapsular
what is parathyroid autotransplantation
–left small or minced into small pieces–transplanted into a small incision on sternothyroideus/sternohyoideus muscle, then the muscle is closed–revascularized and functional in 7-21 days (need to treat for hypocalcemia in the meantime!)
complications of thyroidectomy
–hemorrhage–dyspnea–laryngeal paralysis–megaesophagus (if both vagus injured)–horners–hypothyroidism (rare in cats)–hypoparathyroidism–hypocalcemia–recurrence of dz (hyperthyroidism or carcinoma)
most serious complication of bilateral thyroidectomy
hypoPTH and resultant hypoCacats with ectopic PTH (up to 50%) is not enough to maintain normocalcemia78% dogs developed hypoCa with bilateral thyroidectomy/parathyroidectomy for carcinoma
clinical signs of hypoCa
–restlessness–muscle twitching–facial pruritis–panting–tetany
treatment for acute hypoCa
–Calcium gluconate 1 ml/kg IV slow with ECG or as a CRI in fluids–maintenance therapy with oral vitamin D and calcium; active form of vitamin D (calcitriol) can also be given orally hypoCa should resolve over 21 days, start taper over 8-16 weeks, maintain calcium in low normal range
recurrence rate of hyperthyroidism in cats following bilateral thyroidectomy
10%
what is the treatment of choice for hyperthyroid cats
radioactive iodine I-131permanent tx, make sure kidneys work(may need higher I 131 to treat carcinomas)
behavior of canine thyroid tumors
90% detected clinically are malignant (papillary, follicular, compact, or anaplastic)40% have detectable mets at time of diagnosismost are nonfunctional (10% functional–hyperthyroid: almost always associated with malignancy)
diagnostic approach for canine thyroid tumor
–PE (palpate cervical neck well)–cbc. chem. UA–coagulation panel–thyroid panel (<10% are functional but highly SP for malignancy)–thoracic imaging –cervical US +/- aspirate cytology (not often diagnostic) +/- biopsy (RISK HEMORRHAGE)–CT/MRI if indicated–scintigraphy if indicated
