Natural History and Surgical Outcome of Incidentally Discovered Clinically Nonfunctioning Pituitary Macroadenomas

Objectives: The incidental diagnosis of nonfunctioning pituitary macroadenomas (NFPMAs) is becoming more prevalent with the spread of modern brain imaging techniques. We sought to uncover new data about their natural history and surgical outcome.

Design: This is a retrospective single-center observational study.

Methods: Among 210 patients seen for a NFPMA between 2010 and 2019, 70 (33%) were discovered incidentally (i-NFPMA). We analyzed outcomes in a total of 65 patients with available follow-up data.

Results: Mean age at diagnosis (± s.d.) was 60 ± 14 years and mean maximal diameter was 20.0 ± 7.3 mm. At diagnosis, 29 patients (45%) had pituitary hormone deficits (LH/FSH 41%, TSH 29%, ACTH 15%) and 12% had visual field deficits. 26 patients underwent initial surgery, while 12 had delayed surgery after initial surveillance. In the surveillance group, the risk of tumor growth was estimated at 10%/year. Patients with hormonal deficits at diagnosis experienced earlier growth at 24 months (P < 0.02). Overall, surgical resection of the i-NFPMA led to stable or improved endocrine function in 91% of patients, with only 6% postoperative permanent diabetes insipidus. Moreover, surgery was more effective in preserving intact endocrine function (10/12) than restoring altered endocrine function to normal (6/22, P = 0.03).

Conclusion: About one-third of NFPMAs are now discovered incidentally and a significant subset may be responsible for unrecognized endocrine and visual deficits. Under surveillance the risk of further tumor growth is significant (10%/year) and seems to occur faster in patients already harboring an endocrine deficit. Early surgical removal before onset of endocrine deficits appears to lead to better endocrine outcome.