The pituitary gland plays a pivotal role in many aspects of growth and development as well as the maintenance of a delicate metabolic equilibrium. It operates as part of the hypothalamus–pituitary–adrenal (HPA) axis. Disruptions in any of its many regulatory pathways can lead to significant dysfunction.
Panhypopituitarism is the absence or inadequate production of most pituitary hormones while hypopituitarism (HP) refers to the case in which one or a few hormones are deficient. PHP can be congenital or acquired. Congenital HP is often the result of midline defects, and present with just hypopituitarism, not panhypopituitarism. Acquired PHP can be due to a neoplastic mass effect, infection, ischemic injury, radiation injury, or trauma.
Pituitary adenomas are the most common cause of HP in adults. They compress tissue, impair blood flow, and disrupt hormone delivery by obstruction the portal system. Traumatic brain injuries are increasingly being recognized as yet another cause of PHP. Injuries to the pituitary stalk or the gland directly can cause local hemorrhage compressing the gland or a disruption of the vascular supply of the gland leading to infarct. Pituitary apoplexy results from a sudden infarction or hemorrhage into the pituitary gland. Apoplexy usually selectively affects the anterior pituitary gland. Hypothalamic disease can also lead to PHP, due to the complete deficit of upstream hormones to signal to pituitary gland.
Acute postpartum hemorrhage leads to “Sheehan’s syndrome”: pituitary dysfunction secondary to the massive blood loss and resultant ischemic injury. The pituitary gland is especially at risk in pregnant patients due to the hypertrophy of lactotroph cells that produce prolactin. The hypophyseal vessels constrict in response to acute blood loss, leading to a vasospasm induced necrosis of the gland.
The presentation varies depending on degree of pathways that are affected. PHP can present as adrenal insufficiency (adrenocorticotropic hormone [ACTH]), hypothyroidism (thyroid stimulating hormone [TSH] deficiency), hypogonadism (gonadotropin deficiency), or polyuria/polydypsia (antidiuretic hormone [ADH] deficiency). If the cause of PHP is due to a space occupying lesion, the patient may present with headaches, diplopia or visual field deficits, as the mass impinges on the cranial nerves running near the sella turcica. Careful identification of the deficient hormones and judicious replacement is the mainstay of therapy.
Diagnosis consists of measuring serum levels of the pituitary hormones, their upstream, and their downstream regulatory factors. Imaging studies of the sella turcica can help distinguish intracranial etiologies of HP and PHP from downstream defects.
Treatment targets the underlying cause, replaces hormone deficiencies and addresses the clinical manifestations of the deficiencies. This threefold approach thus depends on the etiology and pathophysiology of the PHP. If the cause is apoplexy from a mass effect from an adenoma or other invasive, compressive force, an emergent surgical resection ...