What is the role of imaging studies in the workup of prolactinomas?

Updated: Mar 25, 2018
  • Author: Venkatesh Babu Segu, MD, MBBS, DM; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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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. [24] 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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