Pituitary Flashcards
Another name for the pituitary gland
Also known as the hypophysis
What does the pituitary do
It releases hormones produced by the hypothalamus which either inhibit or stimulate other organs to release their hormones.
Structure of the pituitary gland
Pea-sized structure made up of 2 lobes, each of which has different functions
Where is the pituitary gland located
Situated in a bony hollow beneath the base of the brain. This bony hollow is called the sella turcica or the pituitary fossa.
Where is the Hypothalamus located
It is situated in the brain at the base of the optic chiasm (posterior to the orbits, where the optic nerves partially cross)
Hypothalamus function
It acts as a collecting centre for information about with the internal environment of the body and uses much of this information to regulate the secretion of the hormones produced by the pituitary gland.
hypothalamic-pituitary axis
hypothalamus is actually attached to the pituitary gland via a stalk-like structure.
Made from the hypothalamus and pituitary gland
Why is the sella turcica important for skull x-rays
his is an important feature for radiographers – we check there is no rotation of this on lateral skull x-rays and on a lateral cervical spine x-ray also. This can be enlarged or eroded which may indicate certain pathologies.
Its where the pituitary gland sits
Anterior pituitary (one lobe of the pituitary. Alternative name, origin and how is it connected to the hypothalamus
Adenohypophysis
Glandular epithelium
Vascular
Posterior pituitary (one lobe of the pituitary. Alternative name, origin and how is it connected to the hypothalamus
Neurohypophysis
Nervous tissue
Neural
Posterior pituitary, how does it work
Hormones are synthesised in the hypothalamus, travel down neurons to the posterior pituitary where they are released into the blood stream. Two of these neurohormones (hormones secreted by neurons) are secreted by the posterior pituitary, these are anti-diuretic hormone (ADH) and oxytocin. (posterior pituitary is an extension of hypothalamus)
What is the feedback loop for the Posterior pituitary
Positive feedback loop
What is the feedback loop for the The Anterior Pituitary
negative feedback loop
The Anterior Pituitary, how does it work
The release of hormones from the anterior pituitary is under the control of the hypothalamus and many of these hormones are released with a diurnal rhythm as environmental stimuli (such as day/night or sleep patterns) influence the hypothalamus.
The hypothalamus controls the hormonal output of the anterior pituitary via releasing and inhibiting hormones that are secreted into local blood vessels that connect the hypothalamus to the anterior pituitary. These hormones act on the anterior pituitary controlling the release of its hormones into the blood stream.
Several hypothalamic-pituitary hormones are termed trophic, meaning that they exert their effects on other endocrine glands, influencing hormone release elsewhere in the body. An example of this is thyroid-stimulating hormone (TSH) released by the anterior pituitary that causes the release of thyroid hormone by the thyroid gland.
What is the Optic Chiasm
The optic chiasm, or optic chiasma, is the part of the brain where the optic nerves cross and is therefore of primary importance to the visual pathway. It is located at the base of the brain inferior to the hypothalamus, and approximately 10 mm superior to the pituitary gland within the suprasellar cistern.
Indications for performing MRI pituitary
Hormonal imbalance
Patient’s symptoms relate to the specific hormone that is being over-produced or under-produced
Pituitary tumours may cause over or under production of the hormone
Visual field defects
This represents a surgical emergency so scans may be performed on an urgent basis
Cushings disease, what is it, what is it caused by and what are symptoms
Caused by over-production of adrenocorticotropin by the pituitary gland
Most commonly caused by pituitary adenoma
Symptoms include:
Weight gain
High blood pressure
Excess hair growth
Fatigue
Should be differentiated from Cushings syndrome
Has very similar symptoms but describes the collection of symptoms
Adrenocorticotropin, what gland produces it?
ACTH is produced in the anterior pituitary gland
Adenomas, classified into?
how do they present?
Present either due to hormonal imbalance or mass effect on adjacent structures
Classified into:
Microadenomas – less than 10mm in size
Macroadenomas – greater than 10mm in size
Secrete the hormone produced by their source cell:
ACTH (as in Cushings Disease)
Prolactin
Growth hormone
May be non-functioning – most likely macroadenomas
Microadenomas are often less than 2mm in size
Pituitary MRI - Technique
Axial T2 whole brain
Coronal T2 through pituitary – 3mm slices
Sagittal T1 through pituitary – 3mm slices
Give gadolinium-based contrast
Sagittal T1 through pituitary – 3mm slices
Coronal T1 through pituitary – 3mm slices
Dynamic scanning may be performed to demonstrate delayed enhancement of an adenoma
Pituitary adenoma enhancement
The pituitary enhances quite uniformly with IV contrast
Pituitary adenomas also enhance with IV contrast but at a different rate
Microadenomas enhance more slowly than macroadenomas
Careful timing of post contrast scanning is necessary to ensure microadenomas are conspicuous from the pituitary gland
Treatment for pituitary adenomas
Medical treatment to control hormone levels
Often has unacceptable side effects
Surgical removal of pituitary adenoma
Only if identified on imaging
Some may be too small to see
Pituitary gland itself is left in situ to preserve function
Performed with transphenoidal approach
For Cushings syndrome:
Removal of both adrenal glands to halt cortisol production
Patient will be on medication for the rest of their life
Post operative imaging for pituitary gland?
MRI is used to evaluate the pituitary post operatively
Patients should have a MRI scan within 48 hours following surgery
Beyond this time-frame inflammatory reaction to the operation makes pituitary MRI difficult to interpret
If there is residual adenoma surgeons may decide to re-operate during the same admission
Beyond this most patients are monitored biochemically
