1.3 Thyroid and Parathyroid Pathology

For review, describe the anatomy of the thyroid gland (or just read)

majority is hormone secreting epithelial cells lining colloid filled follicles

parafollicular cells scattered between follicles

many capillaries

internal parathyroid glands embedded within gland

why is the thyroid gland anatomically unique?

the final assembly of hormone takes place outside the cell in the follicular lumen

T/F secretion of thyroid hormone is by extension of microvilli by follicular cells, phagocytosis of colloid, release of active thyroid hormone and diffusion of of cells into nearby capillaries

true

T/F Antithyroid drugs, such as methimazole or carbimazole, inhibit production of thyroid hormones, but they do not slow or stop the progression of thyroid pathologic condition. The longer medical management is used, the larger the thyroid tumor becomes!

True

Nodular hyperplasia and adenomas of the thyroid glands are most commonly seen in what species? (3)

dogs

cats

horses

are nodular hyperplasias and adenomas typically seen in younger or older animals?

older

are nodular hyperplasias and adenomas of the thyroid glands typically functional, nonfunctional, or either?

nonfunctional EXCEPT in cats

what species are follicular carcinomas of the thyroid gland seen in?

dogs

how do follicular carcinomas of the thyroid gland differ grossly from adenomas?

larger

coarsely multinodular

often have necrosis, hemorrhage, and invasion into surrounding structures and vessels

are follicular carcinomas of the thyroid gland more or less likely to be mobile than adenomas? Why?

less, invasion into surrounding structures and scarring fixes it

are follicular carcinomas of the thyroid gland more or less likely to be bilateral than adenomas?

what fraction of follicular carcinomas are mobile? What fraction are fixed?

more

1/3 mobile

2/3 fixed

do follicular carcinomas tend to be functional, nonfunctional, or either?

Nonfunctional

what is an associated metastases pathology of follicular cell carcinomas?

why does this happen?

multiple "cannonball" pulmonary metastases

direct access to jugular veins

T/F when considering follicular cell carcinomas, it is important to remember that there can be ectopic thyroid tissue present anywhere along the ventral neck from the chin to the base of the heart... and even within the heart

true

nodular hyperplasia, adenomas, and carcinomas of the thyroid gland are (choose one: common/rare) in horses

rank which are more common (hyperplasias and adenomas vs carcinomas)

rare

hyperplasia and adenomas > carcinomas

functional tumors of the thyroid glands are very (choose one: common/rare) in horses and most thyroid tumors are (choose one: small/large) and __________ at necropsy

rare

small

incidental

Are thyroid tumors typically unilateral or bilateral in horses?

unilateral

What is the poster child of c-cell tumors?

adult to aged bulls on high calcium diets (chronic stimulation of gland?)

C-cell tumors are occasionally part of a multiple endocrine neoplasia syndrome which include what other endocrine diseases?

bilateral pheochromocytoma

pituitary adenomas

How do c-cell tumors look grossly?

often very large, firm and multilobulated on cut surface (often tough to cut with all the collagen)

How do c-cell tumors appear histologically?

large areas of dense hyalinized fibrous stroma that may contain amyloid

T/F C-cell tumors can progress to carcinoma

true

what species is idiopathic thyroid atrophy most commonly seen in?

dogs

is idiopathic thyroid atrophy typically a condition of young or geriatric animals?

geriatric

idiopathic thyroid atrophy is characterized by progressive loss of _______ tissue with replacement by ________ tissue and minimal to no inflammation

thyroid

adipose

how does idiopathic thyroid atrophy appear grossly?

smaller and lighter (tan), with collapse of follicles

what species is lymphocytic thyroiditis most commonly seen in?

dogs

What kind of disease is lymphocytic thyroiditis?

autoimmune disease

T/F there are breed predispositions with lymphocytic thyroiditis and both cellular and humoral mechanisms are involved with its pathology

true

there are autoantibodies against what hormones with lymphocytic thyroiditis? (3)

thyroglobulin

T4

T3

what does end stage lymphocytic thyroiditis look like?

atrophy

What are pathologies associated with hypothyroidism of any etiology? (5)

hyperkeratosis

hyperpigmentation

myxedema of the dermis and subcutis (tragic facial expression)

atherosclerosis

glomerular lipidosis

______: gross enlargement of the thyroid glands due to diffuse hyperplasia or increased colloid

goiter

goiters are most commonly seen in what species? (3)

horses

goats

cattle

what are potential causes of goiters? (5)

dietary iodine deficiency

dietary iodine excess (foals)

goitrogenic compounds (plants)

genetic congenital goiter

Idiopathic (problem with receptors?)

with dietary iodine deficiency, the thyroid adds more _________ cells through hyperplastic axis to tell it to increase production

follicular

with dietary iodine excess, ________ material exceeds reserve capacity of the gland

colloid

what are associated pathologies of congenital goiters? (6)

Prolonged gestation

dystocia

myxedema

alopecia

swollen tongue, edematous

larynx and fauces (asphyxiation)

are calves or small ruminants more resistant to the detrimental effects related to congenital goiters?

calves

T/F congenital goiters are common in dogs and cats

false; they are rare

congenital goiters in dogs and cats can fall into what categories?

primary- thyroid

secondary- pituitary

tertiary- hypothalamus

degree of thyroid enlargement related to congenital goiters in dogs and cats is dependent on what?

Cause

what are associated pathologies of congenital goiters in dogs and cats?

disproportionate dwarfism

impaired mental status

Switching to parathyoid pathology

righteous

___________ _______: typical endocrine organ with cells arranged in packets and perivascular palisades with many intimately associated capillaries

parathyroid gland

what cells compose the parathyroid gland?

chief cells (both acitve and inactive)

stimulation of the parathyroid gland is by circulating levels of ________

calcium

what happens with the parathyroid gland when blood levels of calcium are too low? Too high?

too low -> parathyroid secretes PTH -> increases calcium

too high -> c cells secrete calcitonin -> calcium decreases

Low levels of calcium due to nutritional deficiencies or renal disease will leads to chronic (choose one: over/under)stimulation of the parathyroid gland and therefore, (choose one: atrophy/hyperplasia) of the gland

overstimulation

hyperplasia

T/F hyperplastic nodules, adenomas, and carcinomas of the parathyroid gland can all be functional

true

___________ ________: result from the duct between the developing parathyroid gland and thymus persisting and becoming dilated and fluid filled

Parathyroid cysts

what species do parathyroid (kursteiner's) cysts commonly affect?

dogs

cats

T/F parathyroid cysts tend to be common and benign

true

where can parathyroid cysts be located? (2)

close to or in the parathyroid

cranial mediastinum

what lines parathyroid cysts?

cuboidal often ciliated epithelium

what species is diffuse hyperplasia of the parathyroid gland most common in?

dogs

what causes diffuse hyperplasia of the parathyroid gland?

secondary to chronic stimulation by low calcium levels

T/F only part of the parathyroid gland is affected with diffuse hyperplasia

False; ... diffuse babe, all the glands are affected

T/F diffuse hyperplasia of the parathyroid gland is different from nodular hyperplasia which can be single or multiple, functional or not, and may represent early transition to adenoma

true

what species are parathyroid adenomas most common in?

Dogs

T/F parathyroid adenomas are very often functional and secrete PTH

true

describe gross appearance of parathyroid adenomas

well-demarcated and encapsulated, generally solitary, compress adjacent gland

parathyroid adenomas leads to ______ if other glands and c-cell __________

atrophy

hyperplasia

Is parathyroid carcinoma common?

Can they be functional if so, what do they secrete?

nah

yah, PTH

What is distinction between parathyroid adenomas and carcinomas based on? (4)

capsular invasion

increased cellular pleomorphism

mitoses

vascular and local invasion

what pathologies are associated with hyperparathyroidism of any etiology?

Fibrous osteodystrophy (with thinning of cortex and increased fracture rate in many bones)

facial hyperostosis with loss of teeth

_______ __________: hyperparathyroidism associated pathology characterized by thin, poorly mineralized bone trabeculae with increased osteoclast activity and wide separation by fibroblasts and loose connective tissue

fibrous osteodystrophy

What tumors in dogs are associated with humoral calcemia of malignancy (pseudohyperparathyroidism) and are functional, secreting PTHrp? What tumors in cats do this?

are these technically parathyroid tumors?

dogs: AGASACA, lymphoma

cats: lymphoma, bronchogenic, carcinoma, squamous cell carcinoma

no