The pituitary gland lies in the pituitary fossa (sella turcica), which is situated in the middle cranial fossa at the base of the brain. It is linked functionally to the hypothalamus by the pituitary stalk. The hypothalamus lies in a superior position to the pituitary gland, and the link between the 2 organs is critical for normal pituitary gland function.
The anterior pituitary secretes growth hormone (GH), thyrotropin or thyroid-stimulating hormone (TSH), corticotropin or adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. The posterior lobe secretes arginine vasopressin (also called antidiuretic hormone) and oxytocin.
Pituitary masses may be classified based on their underlying etiology: for example, pituitary adenoma, pituitary hyperplasia, nonadenoma tumors, and vascular, inflammatory, or infective lesions. Most pituitary masses are caused by a pituitary adenoma; these may be classified as microadenomas (<10 mm) or macroadenomas (>10 mm).  
Pituitary masses may present with a typical clinical syndrome resulting from hypersecretion of ≥1 anterior pituitary hormones (e.g., Cushing disease, acromegaly). Alternatively, they may present more insidiously with mass effect or with tumor expansion leading to compression of surrounding structures, including normal pituitary tissue, resulting in hypopituitarism. Functional pituitary tumors can produce a complex picture of combined hormonal excess and/or deficiencies.  Pituitary masses may also be found incidentally on autopsy and on imaging with a prevalence ranging from 0.10% to 0.38%, with a mean prevalence of 22.3%.   A combined analysis of both radiologic and autopsy data yielded a final prevalence rate of incidental pituitary adenomas of 16.7%.  Almost all of these are clinically silent microadenomas. The prevalence increases with age, and detection is more likely using high-resolution MRI sequences. 
Professor of Medicine
Division of Endocrinology
University of Florida
JMC declares that he has no competing interests.
Dr Joe M. Chehade would like to gratefully acknowledge Dr Senan Sultan, a previous contributor to this monograph. SS declares that he has no competing interests.
Reader in Neuropathology and Honorary Consultant in Neuropathology
Department of Clinical Neuroscience
Division of Neuroscience and Mental Health
Faculty of Medicine
FR declares that he has no competing interests.
Pituitary Tumor and Neuroendocrine Program
Medicine and Neurosurgery
David Geffen School of Medicine at UCLA
TH declares that he has no competing interests.
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