Pituitary Microadenomas Workup

Updated: Nov 16, 2020
  • Author: Bernard Corenblum, MD, FRCPC; Chief Editor: George T Griffing, MD  more...
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Workup

Laboratory Studies

Current management strategies are controversial. [16] 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, 2]  since prolactin-secreting microadenomas are the most frequent secretory microadenomas.

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. The presence of Cushing syndrome needs to be clinically differentiated from that of the more common simple obesity or polycystic ovarian syndrome.

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%); in contrast, the incidental finding of a nonsecreting microadenoma is sufficiently common that the diagnosis of a corticotropin-secreting adenoma after positive clinical and biochemical testing may then require specialized tests such as petrosal sinus sampling to confirm the anatomic diagnosis.

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. [14, 15]

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Other Tests

Other tests are dictated by the clinical picture of hormonal excess or, very rarely, hormonal deficiency. In contrast to macroadenomas, pituitary function testing is generally not needed for microadenomas. In addition, unlike pituitary macroadenomas, microadenomas rarely cause visual-field defects, and if there is no involvement of the optic chiasm on MRI, there is no need to perform the associated test.

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Histologic Findings

If the tumor is removed surgically, immunohistochemical staining for secretory granules is advisable. If the test is negative and if it is clinically indicated, transcription factor immunostaining may identify the cell of origin for the adenoma. [17]

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Staging

Staging is determined primarily by the size of the microadenoma. By definition, all are less than 10 mm and are likely confined to the sella.

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