the pituitary gland - anatomy and pituitary tumours Flashcards
why do pituitary tumours usually present?
as either a result of compression of surrounding structures or the effect of hormone excess
what clinical syndromes can a pituitary tumour present with?
- acromegaly (GH)
- cushings disease (ACTH)
- prolactinoma (PRL)
- TSHoma (TSH)
- check for hyperprolactinaemia
non functioning pituitary tumour may present with hypopituitarism or compressionn of local structures
- can compress on optic chasm, usually causing bi temporal hemianopia. (asses visual fields)
how does hypopituitarism affect hormone levels?
usually all hormones go down apart from prolactin, which goes up due to disinhibition hyperprolactinaemia.
what are the basal tests for pituitary tumours?
- prolactin and TSH don’t fluctuate much so can be checked at any time of day
- check fT4 and TSH as TSH is usually normal in secondary hypothyroidism
- LH and FSH in first 5 days of menstrual cycle in women
- LH and FSH and basal testosterone checked at 0900 in fasting state in men
- check basal cortisol at 0900 when deficiency is suspected
- IGF-1 = a marker of GH, low levels suggest GH deficiency, high levels suggest excess
what are the dynamic tests for pituitary tumour?
1) the Syncathen test
used to asses pituitary ACTH reserves (Also primary adrenal failure).
After two weeks of ACTH deficiency, atrophy of the adrenal cortex leads to an inadequate response to synacthen
not to be used in an acute situation
2) Insulin tolerance test
gold standard test of ACTH and GH reserves
Insulin-induced hypoglycaemia is a significant physiological stress, and if frank hypoglycaemia is achieved with symptoms, ACTH and GH will rise.
why should the insulin tolerance test not be done in patients with IHD or epilepsy?
risk of triggering coronary ischaemia and seizures respectively
what imaging can be done of pituitary tumours?
MRI
pituitary vows with injections of contrast can show tumour from normal gland
CT may be needed in patients who can’t have MRI
what are pituitary tumours
> 1cm and
<1 cm termed as
> 1 cm are macro adenomas
<1 cm are micro adenomas
where can the pituitary gland be found?
in the sella turcica
where are the anterior and posterior pituitary derived from?
anterior pituitary gland, develops from Rathke’s pouch which grows superiorly from the roof of stomodeum (up growth of gut)
posterior pituitary develops from the neuroectodermal layer called infundibulum. This grows inferiorly from the floor of the diencephalon (down growth of primitive brain tissue)
what are the 5 pituitary axes?
1) growth axis
2) adrenal axis
3) gonadal axis
4) thyroid axis
5) prolactin axis
what are the features of the growth axis?
GH is secreted in a pulsatile manner, with peak pulses during REM sleep
GH acts on the liver to produce IGF-1, a marker of GH activity.
GH and IGF-1 act directly on their receptors
important in musculoskeletal growth in children
GH is under positive control by GHRH and negative controls by somatostatin
what are the features of the ACTH secretion?
ACTH has a circadian rhythm, with peaks in the early morning and lowest at midnight
ACTH stimulates cortisol release and is under positive control by CRH. Cortisol has a negative feedback effect on ACTH
what are the features of the gonadal axis?
- FSH causes ovarian follicle development in women and sperm production in men
- LH causes mid cycle ovulation during LH surge and formation of corpus lute
- In men, LH drives testosterone secretion from leydig cells of testes
- FSH and LH are stimulated by pulsatile GnRH
- testosterone and oestrogen inhibit LH and FSH, and prolactin has an inhibitory effect as well
what are the key features of the thyroid axis?
TSH drives thyroxine release via stimulation of
TSH receptors in the thyroid gland.
TRH stimulates TSH secretion, and is a weak stimulator of prolactin secretion.
Thyroxine has a negative feedback effect on TSH
