Introduction to pituitary disorders

The hormones secreted by the anterior pituitary gland are:

• adrenocorticotrophic hormone (ACTH)
• thyroid stimulating hormone (TSH)
• growth hormone
• prolactin
• follicle stimulating hormone
• luteinising hormone.

The hormones secreted by the posterior pituitary gland are:

• arginine vasopressin (also known as antidiuretic hormone)
• oxytocin.

Pituitary disorders are most commonly caused by sellar or parasellar masses, the majority of which are pituitary adenomas. Refer patients with a sellar or parasellar mass to an endocrinologist for a differential diagnosis, and assessment of pituitary function.

Other causes of pituitary disorders include surgery, radiation, infection, trauma, congenital defects and certain drugs. A disorder of the hypothalamus can cause a secondary pituitary disorder. In children, craniofacial dysmorphic features and eye anomalies (especially midline clefts and optic nerve hypoplasia) suggest problems with hypothalamic–pituitary development.

The signs and symptoms of a pituitary disorder can be related to an excess or insufficient secretion of pituitary hormones, as well as pressure effects of a mass (eg headache, visual disturbances). The onset can be acute or insidious.

The resilience of the individual pituitary cell types to the various causes of pituitary disorders varies. In hypopituitarism related to pituitary compression, the order of diminished pituitary hormone reserve is usually growth hormone, follicle stimulating hormone, luteinising hormone, thyroid stimulating hormone then adrenocorticotrophic hormone. Prolactin deficiency is rare, except in patients with complete pituitary disruption or genetic syndromes. Prolactin secretion is under tonic inhibitory control, so any disruption typically causes hyperprolactinaemia.

Management of pituitary disorders depends on the aetiology and severity of the disorder, and should usually be determined by a specialist.

For a pituitary mass causing altered hormone secretion or pressure effects, transsphenoidal surgery is usually indicated; craniotomy is rarely indicated. Nonfunctioning adenomas can often be observed without intervention if they are not a threat to vision and if pituitary function is normal. Some disorders, such as prolactinoma, are typically managed with drug therapy.

For a pituitary disorder causing hormone deficiency, replacement therapy can be required short term (eg before surgical correction), or indefinitely. Some deficiencies do not require immediate intervention, but prompt replacement therapy is required for:

• cortisol deficiency (caused by adrenocorticotrophic hormone deficiency)
• thyroid hormone deficiency (caused by thyroid stimulating hormone deficiency)
• diabetes insipidus (caused by arginine vasopressin deficiency).