Prolactin Producing Adenomas: Prolactinomas and Hyperprolactinemia

Abstract

Prolactinomas (PPAs) are the most common type of secretory pituitary adenomas. The majority of prolactinomas are found in women on evaluation of amenorrhea, infertility, and new onset or persistent lactation after discontinuation of breastfeeding. Although galactorrhea may also be a sentinel symptom in males, this is not as common, and is often preceded by sexual dysfunction. Diagnosis may not occur, particularly in males or postmenopausal women, until midlife when tumor growth impacts the optic chiasm and/or visual deficits are found, prompting ophthalmology review and subsequent imaging. Likewise, pituitary adenomas may be an incidental finding on a head CT or MRI obtained during a workup for headaches, after a head trauma, or other symptoms.

In addition to a brain MRI to determine tumor size, location, and characteristics, all pituitary hormonal expressions are usually evaluated. Both macroadenomas (MA) and microadenomas (mA) may cause anterior pituitary hormone deficits, and further dynamic testing may be needed. Posterior pituitary hormone deficits are quite rare and would only occur with very large tumors. Prolactin (PRL) assays may vary, so obtaining a diluted PRL level is necessary when levels are high in patients with large tumors (usually >3 cm diameter) to avoid misinterpretation of results secondary to the assay “hook effect.” Evaluation of macroprolactin (biologically inactive PRL) may also be needed in patients without symptoms in order to avoid unnecessary treatment.

Treatment may depend on presenting symptoms and deficiencies. However, prolactinomas are most frequently responsive to dopamine agonist (DA) medications that both normalize prolactin levels and can shrink tumors. Normalization of PRL most often restores fertility, resolves galactorrhea, and significantly improves headaches. Likewise, visual deficits will often resolve or significantly improve with tumor shrinkage. Intolerance or resistance to dopamine agonists, tumor growth while on dopamine agonists, co-secretion with another hormone or a need for a biopsy for histopathology are criteria for transsphenoidal tumor resection. Best postoperative results are achieved by an experienced neurosurgeon. However, treatment with medical therapies (DA), other hormone replacements, or radiation therapy may still be needed postoperatively to control prolactin levels or residual tumor growth.