OBJECTIVE The natural history and proper algorithm for follow-up testing of nonfunctioning pituitary adenomas (PAs) are not well known, despite their relatively high prevalence. The aim of this study was to suggest the optimal follow-up algorithm for nonfunctioning PAs based on their natural history.

METHODS The authors followed up 197 patients with nonfunctioning PAs that had not been treated (including surgery and radiation therapy) at the time of detection, in a single center, between March 2000 and February 2017. They conducted a hormone test, visual field test, and MRI at the time of diagnosis and yearly thereafter.

RESULTS The overall median follow-up duration was 37 months. Microadenomas (n = 38) did not cause visual disturbance, pituitary apoplexy, or endocrine dysfunction. The incidence of patients with tumor volume growth ≥ 20% was higher for macroadenomas than microadenomas (13.8 vs 5.0 per 100 person-years [PYs], p = 0.002). The median time to any tumor growth was 4.8 years (95% CI 3.4-4.8 years) for microadenomas and 4 years (95% CI 3.3-4.2 years) for macroadenomas. The overall incidence of worsening visual function was 0.69 per 100 PYs. Patients with a tumor volume growth rate ≥ 0.88 cm3/year (n = 20) had a higher incidence of worsening visual function (4.69 vs 0.30 per 100 PYs, p < 0.001). The tumor growth rate of all microadenomas was < 0.88 cm3/year. The median time to tumor growth ≥ 20% was 3.3 years (95% CI 1.8-3.9 years) in patients with a tumor growth rate ≥ 0.88 cm3/year and 4.9 years (95% CI 4.6-7.2 years) in patients with a tumor growth rate < 0.88 cm3/year.

CONCLUSIONS The authors have devised a follow-up strategy based on the tumor volume growth rate as well as initial tumor volume. In patients with microadenomas, the next MRI study can be performed at 3 years. In patients with macroadenomas, the second MRI study should be performed between 6 months and 1 year to assess the tumor growth rate. In patients with a tumor growth rate ≥ 0.88 cm3/year, the MRI study should be performed within 2 years. In patients with a tumor growth rate < 0.88 cm3/year, the MRI study can be delayed until 4 years.