A pituitary incidentaloma is a pituitary mass discovered incidentally by computed tomography (CT) or magnetic resonance (MRI) of the brain performed for evaluation of an unrelated disease, and when the patient did not show neurological or endocrine signs and symptoms. Despite of increasing incidence, only a few studies have reported on characteristics, natural history, treatment, or follow-up strategy. Moreover no epidemiologic data exist on pituitary incidentaloma in Korean.

We retrospectively enrolled subjects diagnosed as pituitary incidentaloma in Seoul National University Hospital from January 1992 to August 2006. We reviewed baseline demographic findings and the results of basal hormone tests, visual field test, and MRI (or CT) at baseline and during follow-up.

Among 1310 patients with pituitary adenoma, 161 subjects were diagnosed with incidentaloma. The subject age at diagnosis was 49.7 ± 15.5 years, with 84 males. Macroadenoma was more frequent (n = 110, 68.3%). with microadenomas and Rathke's cleft cysts found in 21 and 30 cases, respectively. The mean diameter of the tumor was 1.75 cm. Functional incidentalomas such as prolactinoma or acromegaly were found in 31 cases (19.3%) although there were no symptoms or visual field defects. Of 61 incidentaloma patients who did not undergo surgery or other treatment over one year, only 3 patient showed an increase in tumor size during the mean 38.0 ± 24.9 months follow-up.

Pituitary incidentaloma generally showed a benign course despite the high prevalence of macroadenoma (68.3%). However, as about 20% of the patients had functioning tumors, pituitary hormonal evaluation at diagnosis is mandatory. Furthermore, as we experienced 3 cases with increased tumor size during follow up, including a case of pituitary microadenoma, long-term careful follow-up of pituitary incidentaloma seems necessary. A long-term, prospective study with more patients would reveal the characteristics and the natural history of pituitary incidentalomas in Korea.