A Non-functioning Pituitary Adenoma Initially Mimicking a Microprolactinoma: The Case for Long-term Follow-up of Patients with Mild Hyperprolactinemia?

Objective: A correct differential diagnosis of patients with mild hyperprolactinemia is essential to select the most appropriate treatment modality.

Clinical Presentation: A 50-yr-old woman presented to our Department for evaluation of an intra- and suprasellar mass causing progressive visual defect. Mild hyperprolactinemia causing menstrual irregularities was diagnosed in February 1989. In 1992, serum PRL levels ranged from 50 to 70 microg/l and magnetic resonance imaging (MRI) of the hypothalamic-pituitary region showed the presence of a 7 mm microadenoma. Bromocriptine therapy resulted in normalization of PRL levels and menstrual cycle, while a repeat MRI showed no change. Menses stopped in March 1998, when the patient was 46 yr old. Subsequently, the patient complained of worsening headaches and, starting from July 2001, visual disturbances. In March 2002, MRI showed a large pituitary tumor, measuring 40x37x28 mm. In May 2002, the patient was operated through the transsphenoidal approach with apparent total tumor removal. Histological examination confirmed a pituitary adenoma that stained negative for all pituitary hormones. Four months after surgery, the patient reported an improvement of visual function. MRI of the hypothalamic-pituitary region, performed 4, 13 and 25 months after surgery, showed a partially empty sella with no evidence of residual tumor.

Conclusions: This case suggests that, to exclude the alternative diagnosis of nonfunctioning pituitary adenoma or another mass lesion of the hypothalamic-pituitary region, repeat neuroimaging studies during long-term follow-up may be advisable in patients with presumed microprolactinoma who did not show reduction of the tumor during dopaminergic therapy.