Pituitary Microadenomas Workup

Updated: Mar 23, 2018
  • Author: Bernard Corenblum, MD, FRCPC; Chief Editor: George T Griffing, MD  more...
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Workup

Laboratory Studies

Current management strategies are controversial. [15] In the absence of symptoms or signs suggesting excess of specific hormones, the most cost-effective strategy is simply measurement of the prolactin level. [1]

If clinical suspicion of Cushing syndrome, acromegaly, or other hormone excess exists, order appropriate tests. Because excess growth hormone secretion may not produce the clinical phenotype in all cases, especially if early in the course, a serum insulinlike growth factor-1 (IGF-1) level is recommended in all cases. Screening tests for Cushing syndrome, such as overnight dexamethasone suppression test, 24-hour urinary free cortisol, or midnight salivary cortisol are usually not routinely performed unless there is clinical suspicion for this disorder.

Autonomous secretion by a tumor usually shows an inappropriate relationship between the level of the hormone secreted by the peripheral gland (thyroid, adrenal, gonadal) and the stimulating pituitary hormone (thyroid-stimulating hormone [TSH], corticotropin, gonadotropins). For example, a patient may be hyperthyroid without TSH suppression (must be differentiated from thyroid hormone resistance) or a patient with Cushing disease may have an elevated or normal (nonsuppressed) corticotropin level.

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Imaging Studies

MRI studies (as seen in the image below) have shown sensitivity and specificity of about 90% for secretory tumors. Enhancement with gadolinium diethylenetriaminepentaacetic acid (DTPA) improves the detection rate. Sensitivity for detection of corticotropin-secreting adenomas is much less (60-75%); diagnosis may require specialized tests such as petrosal sinus sampling.

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

Computed tomography (CT) scans are not very specific or sensitive for microadenomas.

Unless the microadenoma is secretory, the actual pathology remains presumptive. [16, 17]

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Other Tests

Other tests are dictated by the clinical picture of hormonal excess or, very rarely, hormonal deficiency. For larger functional microadenomas, especially those located in an area where upward pressure on the optic chiasm may exist, assessment of visual fields may be useful in monitoring therapy. Computer-assisted perimetry may be more sensitive than Goldman perimetry. In contrast to pituitary macroadenomas, microadenomas rarely cause any visual-field defects.

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Histologic Findings

If the tumor is removed surgically, immunohistochemical staining for secretory granules is advisable. This would be the only definitive tissue diagnosis for the cause of a nonsecreting tumor.

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Staging

Staging is determined primarily by the size of the microadenoma. By definition, all are less than 10 mm.

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