Pituitary Microadenomas 

  • Author: David M Klachko, MBBCh; Chief Editor: George T Griffing, MD   more...
 
Updated: May 18, 2011
 

Background

By definition, a microadenoma (seen in the image below) is a tumor less than 10 mm in diameter. Pituitary adenomas may secrete hormones, or they may be clinically inactive. Many pituitary lesions are discovered while investigating other neurologic problems; these lesions are called incidentalomas.

MRI showing a nonenhancing area in the pituitary cMRI showing a nonenhancing area in the pituitary consistent with a microadenoma in a patient with hyperprolactinemia.
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Pathophysiology

Of the secretory tumors, the most common are prolactinomas. Other secretory tumors may secrete (1) adrenocorticotrophic hormone (ACTH), causing Cushing disease; (2) growth hormone, causing acromegaly; (3) gonadotropins with clinical presentations reflective of severity and sex; or, rarely, (4) thyroid-stimulating hormone (TSH), causing hyperthyroidism. Many secrete inactive alpha-subunits of the glycoprotein hormones. Most incidentalomas are inactive and are of no clinical consequence. As with adenomas in other endocrine glands, all these tumors probably derive from a local mutation, with loss of function of the genes controlling cell proliferation.

The role of genetic mutations was highlighted in a report suggesting that patients with pituitary tumors from 4 Irish families share a common mutation with a patient from the 18th century who had pituitary tumor–mediated gigantism.[1]

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Epidemiology

Frequency

United States

A high-resolution magnetic resonance imaging (MRI) screen of a normal population has shown a 10% prevalence of pituitary lesions.

International

In studies with a total of 10,370 autopsies, the prevalence of pituitary microadenomas was 11%; however, in a Japanese series of 1000 autopsies, many of the midline pituitary lesions were Rathke cysts, not adenomas.

Mortality/Morbidity

Microadenomas do not cause directly attributable excess mortality. These tumors generally are too small to cause bony erosion or to put pressure on the optic chiasm. Any morbidity is caused by excessive hormone secretion.

Race

No race predilection exists.

Sex

Microadenomas may occur in either sex. Prolactinomas are diagnosed more frequently in women, possibly because of the more striking presenting features such as amenorrhea and/or galactorrhea. In men, the diagnosis of inactive adenomas is often delayed until they have become macroadenomas and cause mass effects.

Age

Microadenomas may occur at any age, but prevalence appears to increase with advancing age.

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Contributor Information and Disclosures
Author

David M Klachko, MBBCh  Professor Emeritus, Department of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, University of Missouri

David M Klachko, MBBCh is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, American Diabetes Association, American Federation for Medical Research, Endocrine Society, Missouri State Medical Association, and Sigma Xi

Disclosure: Nothing to disclose.

Specialty Editor Board

Harris C Taylor, MD  Clinical Professor of Medicine, Division of Clinical and Molecular Endocrinology, Case Western Reserve University School of Medicine

Harris C Taylor, MD is a member of the following medical societies: American Association of Clinical Endocrinologists, American College of Physicians, American Thyroid Association, and Endocrine Society

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: eMedicine Salary Employment

Yoram Shenker, MD  Chief of Endocrinology Section, Veterans Affairs Medical Center of Madison; Interim Chief, Associate Professor, Department of Internal Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Wisconsin at Madison

Yoram Shenker, MD is a member of the following medical societies: American Heart Association, Central Society for Clinical Research, and Endocrine Society

Disclosure: Nothing to disclose.

Mark Cooper, MBBS, PhD, FRACP  Head, Diabetes & Metabolism Division, Baker Heart Research Institute, Professor of Medicine, Monash University

Disclosure: Nothing to disclose.

Chief Editor

George T Griffing, MD  Professor of Medicine, St Louis University School of Medicine

George T Griffing, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Medical Practice Executives, American College of Physician Executives, American College of Physicians, American Diabetes Association, American Federation for Medical Research, American Heart Association, Central Society for Clinical Research, Endocrine Society, International Society for Clinical Densitometry, and Southern Society for Clinical Investigation

Disclosure: Nothing to disclose.

References
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MRI showing a nonenhancing area in the pituitary consistent with a microadenoma in a patient with hyperprolactinemia.
 
 
 
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