Key Clinical Questions
How and when do you evaluate pituitary hormonal function?
How do you treat patients with excess or deficient pituitary hormonal function?
How do you classify pituitary tumors?
Which patients with pituitary disease require hospital admission?
What are the indications for consultation with endocrinology and/or neurosurgery?
What are the complications associated with neurosurgical resection of pituitary tumors?
Pituitary disease is more common than popularly supposed. In unselected autopsies, the prevalence of pituitary adenomas averages about 14%. However, the prevalence of clinically significant pituitary adenomas is much lower, about 94 per 100,000 people. Pituitary adenomas can present clinically due to excessive secretion of hormones, impairment of normal pituitary function, neurologic changes due to local compressive mass effects, or hemorrhage. Approximately 30% of survivors of traumatic brain injury and subarachnoid hemorrhage have chronic anterior hypopituitarism; therefore, clinicians must consider this diagnosis in populations at risk, such as wounded combat veterans. Hypopituitarism is also frequent after cranial irradiation, and may complicate pituitary disease of any cause.
PITUITARY ANATOMY AND PHYSIOLOGY
The pituitary gland is located at the base of the brain within the sella turcica, which is the bony roof of the sphenoid sinus. It lies outside the dura mater. The pituitary stalk, containing neurovascular bundles, extends from the hypothalamus through a dural opening to the pituitary gland. This anatomical arrangement renders the pituitary stalk vulnerable to traumatic injury. The optic chiasm is located above the pituitary gland and anterior to the pituitary stalk. The pituitary gland is bordered on the sides by the cavernous sinuses, which consist of vascular lakes containing cranial nerves III, IV, V, and VI and a portion of the carotid artery. The pituitary gland consists of two lobes—anterior and posterior (Figure 154-1).
The hypothalamic-pituitary axis. Hypothalamic nuclei secrete hormones in a pulsatile fashion into a portal venous system, which perfuses anterior pituitary secretory cells and regulates its activity. Posterior pituitary hormones are derived from direct neural extensions from the hypothalamus. (Reproduced, with permission, from Fauci AS, Braunwald E, Kasper DL, et al. Harrison’s Principles of Internal Medicine, 17th ed. New York, NY: McGraw-Hill, 2008. Fig. 333-2.)
The anterior lobe, or adenohypophysis, is made up of secretory cells that manufacture at least six hormones: adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), growth hormone (GH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL). Secretion of the first five hormones is triggered by hypothalamic-releasing factors that travel down the pituitary stalk through a portal venous system. In contrast, anterior pituitary secretion of prolactin, which promotes lactation, is tonically inhibited by hypothalamic secretion of dopamine. Any disorder that compresses or interferes with the pituitary stalk can elevate prolactin levels.
In contrast, the posterior lobe, or neurohypophysis, is comprised of axons of cell bodies arising in the ...