Pathology of the Thyroid Flashcards
from what does the thyroid develop?
evagination of pharyngeal epithelium
descent from foramen caecum to normal location along thyroglossal duct
name 3 common abnormalities in the development of the thyroid?
failure of descent = lingual thyroid
excessive descent = retrosternal location in mediastinum
thyroglossal duct cyst
what are thyroglossal duct cysts?
remnants of the thyroglossal duct
parts of ectopic thyroid tissue left behind as it descends - can become cystic
describe the structure of thyroid tissue?
follicles surrounded by flat to cuboidal follicular epithelial cells
within the centre of each follicle is a colloid
occasional scattered C cells which secrete calcitonin
what is a colloid?
dense amorphic pink material containing thyroglobulin
where are thyroid hormones stored?
in the colloid
what causes release of T3 and T4?
TRH from hypothalamus stimulates anterior pituitary to produce TSH which stimulates thyroid follicular epithelium to produce T3 and T4
T3 and T4 inhibit anterior pituitary and hypothalamus to switch off production
how does TSH cause release of T3 and T4?
TSH binds to TSH receptor on surface of thyroid epithelial cells
G proteins activated with conversion of GTP to GDP and production of cAMP
cAMP increases production and release of T3 and T4
T3 and T4 circulate in bound and free forms
On release T3 and T4……………..
4 types of thyroid pathology?
hyperthyroidism
hypothyroidism
goitre
neoplasia
what are the most common forms of inflammatory thyroid disease?
auto-immune
- hashimotos thyroiditis (hypothyroidism)
- graves disease (hyperthyroidism)
what else can cause inflsmmation in thyroid?
infection
palpation
subacute lymphocytic
de quervains
what causes autoimmune thyroiditis?
familial
concordance in MZ twins
associated with HLA haplotype
polymorphisms in ummune regulation associated genes
- CTLA-4 (negative regulator of T cell response)
- PTPN-22 (inhibits T cell function)
associations with other autoimmune disease
what is thyrotoxicosis?
excess of T3 and T4 (hyperthyroidism)
what can cause thyrotoxicosis?
graves disease (85%)
hyperfunctioning nodules and tumours (adenomas)
TSH secreting pituitary adenoma (rare)
thyroiditis
ectopic production (struma ovarii)
factitious (self medicating with hormones, gland is normal)
who does graves disease usually affect?
females
20-40 yrs old
what is graves disease?
antibodies to TSH receptor, thyroid peroxisomes and thyroglobulin
what are the anti TSH receptor antibodies in graves?
thyroid stimulating immunoglobulin (relatively specific, causes hyperfunctioning)
thyroid growth stimulating immunoglobulin
TSH binding inhibitor immunoglobulins
triad of features in graves disease?
hyperthyroidism with diffuse enlargement of thyroid
eye changes (exophthalmos)
pretibial myxedema
why is there lack of colloid seen in some hyperthyroidism cases?
colloid being continuously exported
what causes hypothyroidism and who does it usually affect?
hashimotos middle aged women associated with other autoimmune disorders associated with HLA-DR3 and DR5 iodine deficiency drugs post therapy ………….
what is hashimotos?
gradual failure of thyroid function due to autoimmune desctruction of …………
what are the antibodies in hashimotos?
anti-thyroglobulin and anti-peroxidase
- cause antibody dependant cell mediated cytotoxicity when bound
mechanism in hashimotos?
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what is hashitoxicosis?
transient release of thyroid hormone which sometimes precedes hashimotos
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what is goitre?
any enlargement of the thyroid
usually due to lack of iodine (dietary or bio-availability)
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what neoplasms can occur in the thyroid?
adenomas (follicular adenoma)
carcinomas (papillary, follicular, medullary, anaplastic)
what are the features of thyroid adenoma?
discrete solitary mass
incidental finding
can cause dysphagia
…………
usually non-functional
can secrete thyroid hormones (thyrotoxicosis)
can present similar to dominant nodule in multinodular goitre or ……carcinoma
what causes thyroid adenoma?
few have mutant ras or PIK3CA
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who do thyroid carcinomas affect?
any age group
female predominance in adults
where are most thyroid cancers derived from?
follicular epithelium (medullary from C cells)
aetiology
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what is the most common thyroid cancer?
papillary carcinoma
describe papillary carcinoma?
solitary nodule in thyroid can be multifocal often cystic may be calcified can be present with lymph node metastases …………………….
how does papillary carcinoma present?
lesion in thyroid gland or cervical lymph node mass local effects - hoarseness - dysphagia - cough - dyspnoea sometimes haematogenous spread to lung ………...
second most common thyroid cancer?
follicular carcinoma
features of follicular carcinoma?
usually females
usually single nodule
slowly enlarging, painless, non-functional
lymphatic spread is rare
haematogenous spread to bone, lungs and liver
invasive growth pattern of follicular carcinoma?
widely invasive??>.#qwmf[pewjg
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