Introduction
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 consistent with a microadenoma in a patient with hyperprolactinemia.
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.
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.
Clinical
History
- Types of pituitary microadenomas
- Incidentalomas usually have no associated symptoms. They are ordinarily found in people who have radiologic studies for other reasons (eg, headaches). Unlike macroadenomas, incidentalomas are too small to cause pressure-related symptoms such as headache or visual field loss.
- Prolactinomas may be asymptomatic if prolactin levels are only slightly elevated. In women, hyperprolactinemia may cause galactorrhea, amenorrhea, or infertility. In men, hypogonadism, erectile dysfunction, and decreased libido may ensue. Gynecomastia may develop but galactorrhea is rare in men.
- ACTH-secreting adenomas cause Cushing disease.
- Growth hormone–secreting adenomas cause acromegaly.
- TSH-secreting adenomas are a very rare cause of hyperthyroidism.
- Gonadotropin-secreting adenomas have been reported. The frequency is unknown. Women may present with amenorrhea and a mismatch between estrogen and gonadotropin levels (eg, elevated gonadotropin levels despite normal or elevated levels estrogen levels without suppression of gonadotropins).
Physical
Any physical abnormalities are caused by excessive hormone secretion (eg, galactorrhea due to hyperprolactinemia, acromegaly due to excessive growth hormone, ACTH-mediated Cushing disease). Many microadenomas found incidentally on CT scan or MRI may be clinically inactive.
- Patients with prolactin-secreting adenomas may present with infertility, galactorrhea, amenorrhea, and loss of libido. Weight gain is frequent and may be reversed in some patients with normalization of prolactin levels.
- Growth hormone–secreting adenomas cause acromegaly with coarsening of facial features and soft tissue swelling of the hands and feet. Most patients complain of excessive perspiration and offensive body odor. Progressive bony proliferation occurs, and the mandible lengthens and thickens, resulting in an underbite.
- ACTH-secreting adenomas cause Cushing disease characterized by weight gain, primarily in the facial, nuchal, truncal, and girdle areas (ie, centripetal or "buffalo" obesity). Protein breakdown leads to thin, friable skin that bruises easily; breakdown may form wide striae and may cause muscle weakness, wasting, and osteopenia. In children, growth is arrested.
Causes
As with adenomas elsewhere, the likely cause of pituitary microadenomas is a local mutation leading to autonomous growth and/or secretion.
More on Pituitary Microadenomas |
 Overview: Pituitary Microadenomas |
| Differential Diagnoses & Workup: Pituitary Microadenomas |
| Treatment & Medication: Pituitary Microadenomas |
| Follow-up: Pituitary Microadenomas |
| Multimedia: Pituitary Microadenomas |
| References |
| Further Reading |
| Next Page » |
References
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Further Reading
Related eMedicine topics:
Acromegaly [Dermatology]
Acromegaly [Endocrinology]
Cushing Syndrome
Hypopituitarism [Emergency Medicine]
Hypopituitarism [Pediatrics: General Medicine]
Hypopituitarism (Panhypopituitarism)
McCune-Albright Syndrome [Endocrinology]
McCune-Albright Syndrome [Pediatrics: General Medicine]
Nasal and Sublabial Approaches to the Pituitary
Pituitary Adenoma
Pituitary Apoplexy
Pituitary Microadenomas
Pituitary Tumors
Prolactinoma
Clinical guidelines:
American Association of Clinical Endocrinologists medical guidelines for clinical practice for the diagnosis and treatment of acromegaly. American Association of Clinical Endocrinologists - Medical Specialty Society
American College of Endocrinology - Medical Specialty Society. 2004 May/June. 13 pages. NGC:003789
Stereotactic radiosurgery for patients with pituitary adenomas. IRSA - Professional Association. 2004 Apr. 12 pages. NGC:003598
Clinical trials:
Assessment of Cardiovascular Risk Markers in Growth Hormone Deficient Patients With Nonsecreting Pituitary Adenomas
Prevalence of Pituitary Incidentaloma in Relatives of Patients With Pituitary Adenoma
Proton Radiation Therapy for Pituitary Adenoma (PI01)
Rosiglitazone in Treating Patients With Pituitary Tumors
Targeted Therapy With Lapatinib in Patients With Recurrent Pituitary Tumors Resistant to Standard Therapy
Keywords
pituitary microadenoma, pituitary, pituitary gland, tumor pituitary, pituitary adenoma, prolactinoma, microadenoma, tumor pituitary gland, pituitary hormone, pituitary hormones, pituitary tumor, pituitary tumors, Cushing syndrome, pituitary macroadenoma, hypophyseal adenoma, acromegaly, epithelial pituitary cells, incidentalomas, secretory tumors, adrenocorticotrophic hormone, gonadotropin-secreting adenomas, ACTH, midline pituitary lesions, Rathke cleft cysts, amenorrhea, galactorrhea, mass effects, prolactin, hyperprolactinemia, hypogonadism
