Pituitary anatomy and intro - booklet

Question 1

Anatomy of pituitary gland

Answer 1

• Size pea
• Sits in pituitary fossa at base of brain

Question 2

Anterior vs posterior origin

Answer 2

• Anterior - derived from upgrowth of gut
• Posterior - downgrowth of primative brain tissue

Question 3

Relationships of pituitary gland

Answer 3

• Optic chiasm above
• Cavernous sinus laterally - containing CN III, IV, Va Vb and VI and internal carotid artery

Question 4

How does hypothalamus act on pituitary?

Answer 4

Secretes inhibiting and releasing factors transported down hypophyseal portal tract to anterior pituitary

Question 5

Axis of pituitary

Answer 5

• Growth axis
• Adrenal axis
• Gonadal axis
• Thyroid axis
• Prolactin axis

Question 6

Growth axis - what happens?

Answer 6

• GH secreted in pulsatile manner
• Peak pulses during REM sleep
• GH acts on liver to produce IGF-1 (marker of GH activity)
• Plays role in MSK growth in children
• Under control of GHRH and somatostatin

Question 7

Adrenal axis - what happens?

Answer 7

• ACTH has circadian rhythm
• Peaks pulses in early morning and lowest activity at midnight
• ACTH stimulates cortisol release
• Positive control of CRH and cortisol has -ve feedback on ACTH

Question 8

Gonadal axis - what happens?

Answer 8

• FSH leads to ovarian follicle development in women, sperm production in men
• LH causes mid cycle ovulation and drives testosterone synthesis in male testes (Leydig cells)
• Stimulated by pulsatile GnRH
• Testosterone, prolactin and oestrogen inhibit FSH and LH

Question 9

Thyroid axis - what happens?

Answer 9

• TSH drives thyroxine release via stimulation of TSH receptors on thyroid gland
• TRH stimulates TSH secretion and also stimulates prolactin (weak)
• Thyroxine has -ve feedback

Question 10

Prolactin axis - what happens?

Answer 10

• Prolactin causes lactation and directly inhibits LH and FSH
• Controlled by dopamine
• Stimulated weakly by TRH
• Anything that blocks dopamine = elevated prolactin

Question 11

How can pituitary tumours present?

Answer 11

• Mass effect - compression of surrounding structures
• Hormone excess

Question 12

Functional pituitary tumours can present as…

Answer 12

• Acromegaly (GH)
• Cushings disease (ACTH)
• Prolactinoma
• TSHoma

Question 13

Non functioning pituitary tumours may present with…

Answer 13

• Compression of local structures
• Hypopituitarism

Question 14

What happens to hormones in hypopituitarism?

Answer 14

Usually all hormones go down except prolactin
This goes up due to disinhibition hyperprolactinaemia - reduced dopamine or compression of stalk dopamine is not released

Question 15

Visual defect of pituitary tumours

Answer 15

Bi temporal hemianopia

Question 16

When is surgery indicated for non-functioning tumours?

Answer 16

Usually if visual defect is present = surgery

Question 17

Basal tests for pituitary tumour

Answer 17

• Prolactin and TSH - anytime
• Women LH and FSH - within 1st 5 days of menstrual cycle
• Men - LH, FSH and testosterone at 9am when deficiency is expected
• IGF-1 is a marker for GH

Question 18

Dynamic tests for pituitary tumour

Answer 18

• Synacthen test
• Insulin tolerance test - gold standard for ACTH and GH reserve
• ACTH and GH should rise with ITT

Question 19

Who should insulin tolerance test not be done on?

Answer 19

• Ischaemic heart disease pts
• Epilepsy
• Risk of triggering coronary ischaemia and seizures

Question 20

Imaging for pituitary tumour

Answer 20

• MRI + contrast
• CT may be adequate if unable to do MRI
• PET and functional MRI increasing popularity to see functionality of tumours

Question 21

Macro vs micro adenoma

Answer 21

• Macro if more than 1cm
• Less than 1cm - microadenoma