8.5 Pituitary Flashcards
(32 cards)
How does a patient with pituitary tumour present?
- Hormonal dysfunction—
could be over/under secretion of pituitary hormones. - Mass effect—
compression of surrounding tissues due to the rapidly growing tumour,
increased intracranial pressure. - Incidentalomas—
with no hormonal or pressure effect.
Diagnosed during imaging for other conditions. - Pituitary apoplexy—
emergency situation with signs of acute hormonal imbalance, meningism, visual impairment and other signs of intracranial pathology.
This is due to infarction or sudden haemorrhage in an already existing pituitary adenoma.
Describe the anatomy of the pituitary gland.
Pituitary is the ‘master gland’,
secreting hormones that control most of the body functions.
It is a pea-sized organ present beneath the hypothalamus
in the sella turcica—
a depression at the base of skull.
It is made up of two types of tissues forming the anterior and posterior pituitary gland.
Anterior pituitary gland
Anterior pituitary gland (adenohypophysis)
is an evagination of the ectodermal Rathke’s pouch
(nasopharynx) containing epithelial tissue.
- Traditionally, three cell types were distinguished
when stained with hematoxylin and eosin.
° Acidophils
stain orange/red and secrete polypeptide hormones—
growth hormone (GH) and prolactin (PRL)
° Basophils
stain blue and secrete glycopeptide hormones—
thyroid-stimulating hormone (TSH), gonadotrophic hormones
(LH/FSH), and adrenocorticotrophic hormone (ACTH).
° Chromophobes
are non staining, due to the nonsecretory nature of
the cells.
How are cells classified
- Currently these cells are classified according to the hormones they
produce.
- ° Somatotropes
make up the majority of the anterior pituitary cells.
They produce GH and are responsible
for 20% of all pituitary microadenomas. - ° Lactotropes
secrete PRL, and prolactinomas are the commonest
cause of pituitary adenomas. - ° Thyrotropes—TSH.
- ° Gonadotropes—LH/FSH
- ° Corticotropes—ACTH
How are these hormones stimulated
The signal for the secretion by these cells comes from the hypothalamus via
individual regulatory hormones.
The hypothalamic and the corresponding pituitary hormones,
their site of action, and their functions are depicted in
Table 8.1.
Posterior pituitary gland
Posterior pituitary gland (neurohypophysis) is an
extension of the brain at the level of the diencephalon
and hence contains neural tissue.
- Made of pituicytes, which are similar to glial cells.
- It does not produce any hormones
but rather stores and releases the hypothalamic hormones
oxytocin ( paraventricular)
and
antidiuretic hormone (supraoptic)
Although each nucleus secretes a small proportion of the other hormone
which then pass through the neural axons into the posterior pituitary.
The terminal portions of the axons,
which store these hormone granules called
Herring bodies,
are closely associated with fenestrated capillaries.
Hypothalamic and pituitary hormones and their functions
- GHRH
Somatotropes—GH
All body cells –
Protein synthesis,
Gluconeogenesis, lipolysis,
sodium and water absorption - PIH
Lactotropes—inhibits PRL secretion
Breast –
Prolactin causes milk production
- GnRH
Gonadotropes—LH/ FSH
Testes, ovaries –
Spermatogenesis, ovarian follicular growth - TRH Thyrotropes—TSH
Thyroid gland
T3 and T4
General growth and metabolism - CRH Corticotropes—ACTH
Adrenal gland
Glucocorticoids Mineralocorticoids
Gluconeogenesis, lipolysis,
sodium and water reabsorption,
anti-inflammatory
- Oxytocin – Breast, kidney – Milk secretion and contraction
of uterus, water retention - ADH – Blood vessel, kidney – Arterial vasoconstriction, water
reabsorption
What is the blood supply of the pituitary gland?
Arterial supply
Superior and inferior hypophyseal arteries,
which are branches of the internal carotid artery.
The superior hypophyseal artery ramifies into the hypthalamo hypophyseal portal circulatory system.
The primary capillary network lies at the pituitary stalk,
where the hypothalamic hormones are released.
This capillary bed is drained by a set of long portal veins that give rise to the
second capillary bed in the anterior pituitary.
The veins originating in the neurohypophyseal capillary plexus give rise to
the short portal veins that will also contribute to the adenohypophyseal
capillary plexus and connect the two circulatory systems.
This hypothalamo-hypophyseal portal system creates a communication
between the endocrine and neural cells providing an easy short-loop
feedback between the two sets of cells.
Venous drainage
Cavernous sinus -> Petrosal sinus -> Jugular vein
What is portal circulation, and what are the other examples in the body?
The portal circulation begins and ends in capillaries.
Arterial capillaries normally end up forming a vein that
enters the right side of the heart.
In portal circulation, the primary capillary network drains into a vein known
as portal vein,
which then branches to form the second set of capillaries before draining into a venous system.
other examples of portal circulation in the body are the
hepatic portal, placental, renal, ovarian, and testicular circulations.
What are the types of pituitary tumours?
Pituitary tumours are responsible for at least three-fourths of all intracranial
neoplasms. Considering the size of tumour, they could be divided as:
Microadenomas
Macroadenoma
Microadenomas
- < 10 mm diameter
- Commonly occurring pituitary adenomas
- Clinical effects are mainly due to hormonal hyper-secretion
Macroadenomas
- > 10 mm in size
- Nonsecretory tumours
- Effects are usually due to mass and pressure effects leading to visual
disturbances, increased intracranial pressure, and hypopituitarism due
to destruction of pituitary tissue.
What are their clinical manifestations?
The pituitary gland is surrounded by structures as shown in Figure 8.6.
so the pressure effects relate to the tissues closely related to the tumour.
Floor—sphenoidal air sinus
Roof—diaphragma sella,
an invagination of dura, which is traversed by the
pituitary stalk, optic chiasm
Lateral walls—cavernous sinus, internal carotid artery, CN III, IV, V1, V2, and VI
explain the control of GH release.
IGF-1 (Somatomedin C) is a hormone that is secreted mainly from the liver
upon stimulation by GH.
The functions of this hormone are similar to the GH and
cause bone and muscle growth along with lipolysis.
As the half life of IGF-1 is longer than the GH and does not have a diurnal variation,
IGF-1 assay is used to diagnose GH excess or deficiency.
What is acromegaly and what are
its features?
Acromegaly is a condition where there is an increased secretion of the GH
in adults.
The term gigantism is used when this occurs before epiphyseal
fusion.
It is a rare condition affecting 6–8 per million.
Airway
Increased size of the skull with prominent lower jaw
and malocclusion, macroglossia,
thickening of the laryngeal and pharyngeal soft tissues,
laryngeal stenosis,
hoarse voice due to recurrent laryngeal nerve palsy.
In a minority of the patients,
there is associated thyroid enlargement leading to tracheal compression.
All these features make acromegaly a recognised
cause of difficult ventilation and intubation.
Careful preassessment, including indirect laryngoscopy,
helps with the choice of intubation technique.
The mallampati grades can be falsely reassuring and every step is taken to
overcome a difficult airway. Awake fibreoptic intubation might be necessary
as is awake tracheostomy.
CVS
cardiovascular
About 30% of acromegalic patients have hypertension.
Myocardial hypertrophy,
interstitial fibrosis,
cardiomegaly leads to ischaemic heart disease
left ventricular dysfunction.
ECG and ECHO are mandatory to assess the cardiac function.
Respiratory
Coarsening of features leading to upper airway obstruction,
spirometry shows an obstructive picture.
The associated obstructive sleep apnoea
requires investigation and appropriate
treatment to reduce postoperative respiratory morbidity.
Neurological
Compression of surrounding structures leading to
visual disturbances,
increased ICP,
cavernous sinus thrombosis.
CN II involvement leads to impaired visual acuity
and bitemporal hemianopia.
CN III, IV, and VI involvement cause ophthalmoplegia and other visual disturbances.
Endocrine
+
Others
Impaired glucose tolerance and diabetes mellitus complicates more than
25% of acromegalic patients.
This necessitates careful glucose monitoring
and treatment with variable rate insulin infusion perioperatively.
There is a high likelihood of high PRL secretion
contributing to menstrual problems in
women and sexual dysfunction in men.
others
Increased size of hands and feet, arthropathy, myopathy, osteoporosis.
How is acromegaly diagnosed
Due to the insidious onset of the condition, the diagnosis can be delayed for
even a decade.
- Clinical appearance
- Signs and symptoms
- Random GH or IGF-1 concentration
- Failure of suppression of GH after 75 mg glucose administration (GTT)
- MRI to look at the size and extent of tumour
what are the different modalities of treatment?
Treatment is aimed at controlling the size and reducing the effects of the
tumour. Untreated acromegaly is associated with a 2 to 2.5 times increased
mortality compared to healthy adults.
- Surgery
Is the mainstay of treatment and is currently done by minimally invasive
endoscopic procedure through the transsphenoidal route. - Drug therapy
° Dopamine agonist —usually Cabergoline.
° Somatostatin analogues—usually octreotide.
This helps to reduce the size of tumour before surgery.
° Growth hormone receptor antagonist—
expensive but has been shown
to normalise the levels of IGF-1.
- Radiotherapy
Takes longer time to work. But with the invention of the ‘gamma-knife’
radiosurgery, remission can be achieved in less time.
What are the anaesthetic concerns in a patient undergoing surgery for acromegaly?
Anaesthetic concerns could be divided according to the factors
pertaining to:
- Neurosurgical anaesthesia and its implications
° Haemodynamic stability
° Maintenance of cerebral oxygenation
° Prevention of perioperative complications
° Rapid emergence to facilitate early neurological assessment
° Adequate postoperative analgesia and antiemesis
° Anaesthesia for transsphenoidal pituitary surgery is not covered in this
question.
- Acromegaly and its implications
