Pituitary Gland lecture Flashcards
Location and relations
Base skull
Sella tursica
Attached to hyppthalamus via stalk
Cavernous sinuses either side
Optic chiasm superiorly
Size of pituitary
13mm x 9mm 100mg
When does pituitary size change?
- Doubles pregnancy
- Shrinks elderly
Blood supply to pituitary
- Hypothalamo-hypophyseal portal system
- Derived from superior and inferior hypophyseal arteries
Venous drainage of pituitary
- Through cavernous sinus into petrosal sinuses and internal jugular veins
Important to know this for venous sampling
What is produced by pituitary gland?
8 hormones
6 anterior - FSH, LH, GH, ACTH, TSH, Prolactin
2 posterior - ADH and oxytocin - just stores these, does not produce
What is hypopituitarism
Partial or complete deficiency of anterior and or posterior pituitary hormones
May be all hormones, partial or singular
Can be primary or secondary due to hypothalamus pathology
Causes of hypopituitarism
- Pituitary or parapituitary tumours eg meningioma, mets
- Radiotherapy
- Infarction - apoplexy, Sheehans
- Infiltration - sarcoidosis, lymphocytic, haemachromotosis
- Infection - eg TB/abscess
- Trauma or SAH
- Isolated deficiencies - Kallmanns
- Genetic
Clinical manifestations of hypopituitarism
- GH - short stature if occurs when under 18, reduced exercise capacity
- FSH/LH - amenorrhoea, anovulation, erectile dysfunction, reduced libido
- ACTH - hyperkalaemia, hypoadrenal crisis
- TSH - hypothyroidism
- PRL - failure lactation
- ADH - polyuria and polydipsia
Investigations for hypopituitarism
- Basal hormone levels (cortisol done at 9am when highest)
- Investigate cause - MRI, serum ACE (sarcoid), hCG, ferritin (haemochromatosis) AFP (tumours)
- Biopsy?
Dynamic testing for growth hormone
- Glucagon
- Arginine
- Insulin tolerance test
All try to stimulate glucagon production
Dynamic testing for ACTH
- Short synacthen test
- Also long - not really used now
Dynamic testing for FSH and LH
GnRH administration
Test for ADH deficiency
- Plasma and urine osmolarity
- Urine Na
- Fluid deprivation test - see if urine concentrates
Signs of hypersecretion of pituitary hormones
Acromegaly
Cushings
Most common brain tumour
Adenoma
Classification of pituitary tumours
- Size - macro vs micro
- Functional vs non-functional
Order of incidence of adenoma types
- Prolactinoma
- Non functioning - mass effect
- GH - acromegaly
- ACTH adenoma -Cushings disease
- TSH adenoma - RARE
Physiological causes of hyperprolactinaemia
- Pregnancy
- Breastfeeding
- Exercise
- Stress
- Sleep
- Seizure
Pharmacologcal causes of hyperprolactinaemia
- Dopamine antagonist - eg haloperidol, risperidone, metoclopramide
- MAO inhibitors - parkinsons
- Cimetidine
- Verapamil
- Thyrotropin releasing hormone test
Pathological causes of hyperprolactinaemia
- Pituitary tumours (prolactinoma)
- Hypothyroidism
- CKD
- PCOS
Presentation of prolactinoma
- Galactorrhoea
- Amenorrhoea/irregular periods
- Reduced libido
- Erectile dysfunction
or mass effect:
* Headache
* CN involvement
* CSF leak
* Hypopituitarism - if compresses
Investigations for prolactinoma
- MRI
- PRL level (less than 2000 suggests micro/stalk effect, more than 4000 means macro)
- Pituitary function tests
What is the hook effect?
Antibodies are bound to some prolactin so some is not read in blood test
If they dilute sample and re do - can trust sample
What is macroprolactin?
Larg
Large aggregates - prolactin appears larger value than it actually is
Use polyethylene glycol to rule out (PEG
What is stalk effect?
High levels of prolactin occur due to compression of pituitary stalk causing reduced dopamine release
= decreased inhibition of prolactin not actually prolactinoma
Aims of treatment for prolactinoma
Micro - restore gonadal function
Macro - reduce size and restore function
Options of treatment for prolactinoma
- Dopamine agonists eg Cabergoline, Bromocriptine, Pergolide, Oestrogen
- Surgery sometimes if compressing chiasm, aggressive
- Radiotherapy sometimes too
Presentation of acromegaly
- Sweating
- Headache
- Tiredness
- Joint pain
- Change in shoe/ring size - enlarged hands and fingers
- Frontal bossing - prominent forehead
- Enlarged nose
- Prognathism - bulging jaw
- Macroglossia
- Carpal tunnel
- Organomegaly
Associated co-morbidies with acromegaly
- HTN
- DM
- OSA
- IHD
- CHF
- Colonic polyps
Acromegaly tests
- IGF1 and random GH - not very helpful
- OGTT - should supress GH to less than 0.33
- MRI
- Pituitary function test
- GNRH - ectopic secretion from carcinoid tumour if no pituitary lesion
Treatment for acromegaly cuased by pituitary tumour
- Transphenoidal surgery
- Radiotherapy
- Medical - somatostatin anologies, dopamine agonists, GH receptor antagonist
Causes Cushings syndrome
- Pseudocushings - alcoholism, severe depression
- Adrenal adenoma/carcinoma/nodular hyperplasia
- Exogenous steroids
- Ectopic ACTH or CRH
Cause of cushings disease
Pituitary adenoma secreting ACTH
Associated features of Cushings
- HTN
- DM
- Osteoporosis
- Recurrent infections
Investigations for Cushings
- 2x 24hr urine cortisol test
- Overnight dexamethasone supression test
- Salivary cortisol
- Midnight cortisol
- Low dose dexamethasone supression test - 100% sensitive almost and then high dose
- ACTH
- K+
- CRH
Ectopic ACTH vs pituitary ACTH test results
Low K - mostly in ectopic
Supression on HDDST - supressed in pituitary (not ectopic)
Rise when CRH given - pituitary
If unsure if pitutary cushings, another invasive test can do?
Inferior petrosal sampling
Compare ACTH to serum
If peripheral ratio is more than 2x suggests pituitary cushings
Ratio of more than 3 after CRH given is diagnostic
Treatment of cushings disease
- Transphenoidal surgery
- Radiotherapy
- Adrenalectomy (can cause Nelsons syndrome)
- Medical - Ketoconazole, Metyrapone
What is Nelsons syndrome?
ACTH production increases when cortisol decreases if remove adrenals
= enlarge tumour
What is diabetes insipidus defined as?
Passage of more than 3L per day of dilute urine
Osmolality less than 300mosm/kg
Clinical symptoms of DI
- Polyuria
- Polydipsia
- Nocturia
2 types DI
- Cranial or nephrogenic
Cause of cranial DI
- Congenitial (DIDMOAD - diabetes insipidus, DM, optic atrophy, deafness)
- Acquired due to trauma, infection, infiltration, inflammation, vascular
Nephrogenic diabetes cause
- Familial
- Acquired - drugs, metabolic, CKD, post obstructive uropathy
DI investigations
- More than 3L per day urine
- Exclude DM, hypercalcaemia, renal failure
- Water deprivation test - if less than 300mosm/kg then diagnostic
- Then do desmopressin admistration to see if osmolarity changes by more than 50% - if it does = cranial
- MRI brain
Treatment of DI
Cranial - desmopressin
Nephrogenic - Indomethacin, Thiazide, high dose desmopressin
How does Indomethacin work?
NSAID - blocks action of prostaglandins at kidney
= less inhibition of ADH
