A giant prolactinoma presenting with unilateral exophthalmos: effect of cabergoline and review of the literature.

We report the case of a 45-year-old male presenting with unilateral exophthalmos due to a large tumoral mass invading the skull base. Ophthalmologic examination did not show any visual field defects. Imaging techniques demonstrated extension of a huge tumor (approx. 8×8×8 cm) into the right orbit and nasopharynx. Endocrine work-up revealed grossly elevated serum prolactin (PRL) levels (26,466 μg/l, nl. <12), pointing to a large, invasive macroprolactinoma. Stimulation tests indicated associated partial adrenal and growth hormone deficiencies. Planned surgery was abandoned, and the patient was instead treated with the long-acting dopamine agonist, cabergoline. Over a period of one year, serum PRL dropped to 131 μg/l, while the tumor mass shrank to less than 50% of its original volume (with 3.5 mg/ week of cabergoline). The exophthalmos disappeared, and the patient did not develop rhinorrhea or any other side effects from treatment with cabergoline. The efficacy was maintained throughout the second year (ultimate serum PRL 74 μg/l, and final size less than 10% of the original). With reference to this case, we review other macroprolactinomas reported in the recent literature for associated exophthalmos, grossly elevated serum PRL levels (≥15,000 μg/l), and/or “giant” size (≥4 cm in maximum diameter). We highlight the use of dopamine agonists in the treatment of prolactinomas with such unusual characteristics.