Prolactinoma Workup

Updated: Mar 31, 2017
  • Author: Venkatesh Babu Segu, MD, MBBS, DM; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Workup

Laboratory Studies

Hormone testing  [18]

Serum PRL - Measure serum PRL levels on 1 or more occasions, especially if the elevation is modest. Do not measure the PRL level directly after performing a breast examination, because the breast examination may cause a physiological PRL elevation.

Serum pregnancy test - Always consider the possibility of pregnancy in reproductive-aged females, because this is the most common cause of secondary amenorrhea in this group.

Serum TSH - Measure TSH levels to exclude the possibility of an elevated PRL level occurring secondary to an elevated TRH level. TRH is one of the PRFs. If the TSH level is elevated, confirm the finding by measuring the free thyroxine level.

Measurement of other pituitary hormones

In a male presenting with symptoms of hypogonadism, measure serum testosterone or bioavailable testosterone levels.

In a patient with a history suggestive of adrenal insufficiency, measure basal and cosyntropin-stimulated cortisol levels.

In a person with features consistent with acromegaly, measure serum insulinlike growth factor-1 levels.

Exclude other possible systemic causes for hyperprolactinemia, such as chronic renal failure or cirrhosis, using appropriate laboratory tests as warranted.

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Imaging Studies

After performing biochemical testing, order a magnetic resonance imaging (MRI) scan of the pituitary hypothalamic area (with gadolinium enhancement) or a computed tomography (CT) scan of the region (with contrast) to determine if a mass lesion is present.

MRI is better for soft-tissue delineation and for the identification of a small lesion. CT scanning is better for the identification of any bone distortion or destruction. Special attention is given to the size of the tumor and its encroachment on surrounding structures (eg, the optic chiasm, other cranial nerves) and resulting effects (eg, bony destruction).

Good correlation exists between the size of the prolactinoma and the degree of elevation of the serum PRL. A serum PRL value of 200 ng/mL or greater in the presence of a macroadenoma (>10 mm) is virtually diagnostic of prolactinoma. However, if the serum PRL value is less than 200 ng/mL in the presence of a large pituitary mass lesion, this is more suggestive of hyperprolactinemia occurring secondary to stalk compression by the lesion; it could also indicate the occurrence of the hook effect, which is an artifact in the lab method used to measure prolactin. [19] Immunoassays used to measure PRL, such as immunoradiometric assay (IRMA), enzyme immunoassay (EIA), and immunochemiluminometric assay (ICMA), employ a "sandwich" (2-antibody) technique. When the PRL level is markedly elevated, the excess antigen (PRL) is washed off in the liquid phase of the sandwich assay and thereby results in gross underestimation of antigen levels in the specimen. When this is suspected, serial dilutions of theserumsamplewill reveal the actual hormone level.

Repeat scans are obtained postoperatively and during follow-up examinations thereafter, or they are obtained after medical treatment to help determine if the tumor has progressed or regressed. The frequency with which repeat imaging scans are performed is individualized to the patient. For instance, in patients with microprolactinoma, pituitary MRI could be performed 1 year after treatment start and then every few years thereafter, less frequently than such scanning would be performed in patients undergoing treatment for macroprolactinoma.

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Other Tests

When the tumor is large and is in close vicinity of the optic chiasm, formal visual-field (VF) testing by an ophthalmologist is performed prior to any therapy. The same testing is repeated after treatment is begun, to monitor the patient's response to treatment.

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Procedures

If a pituitary/hypothalamic lesion other than a prolactinoma (such as lymphocytic hypophysitis or a granulomatous condition) is considered, biopsy of the lesion by a neurosurgeon may be indicated.

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