10 Years' Experience of Using Low-Field Intraoperative MRI in Transsphenoidal Surgery for Pituitary Adenoma: Results of the Swiss Pituitary Registry (SwissPit).

Background: For 20 years, several studies have reported intraoperative magnetic resonance imaging (iMRI) utility to achieve gross total resections in transsphenoidal pituitary adenoma surgery. Although few studies on low-field iMRI included >100 patients, data on hormonally active tumors remain scarce and follow-up times are <3 years. This is not sufficient to judge the long-term efficiency of the use of low-field iMRI. The aim of this retrospective study is to report the detailed outcome of iMRI-controlled transsphenoidal surgery in >200 patients during a follow-up exceeding 5 years.

Methods: Patients undergoing surgery for pituitary adenoma by iMRI-controlled, endoscopically assisted transsphenoidal surgery at the authors' institution between 2006 and 2016 were eligible for inclusion. Data were collected in the Swiss Pituitary Registry. A Polestar 0.15T-scanner was used.

Results: A total of 231 patients had surgery for 160 nonfunctioning adenomas; 28 hGH-, 27 PRL-, 10 ACTH-secreting and 6 mixed adenomas and were followed for 62 months (9-178). Additional iMRI-guided resections were possible in 54% and increased the gross total resection rate by 4% (P = 0.004). Remission rates were as follows: nonfunctioning adenoma, 53%; acromegaly, 61%; prolactinoma, 50%; Cushing disease, 90%. Tumor regrowth and recurrence was detected at a mean time of 24 and 63 months, respectively. Recovery of deficient hormone axes was detected in 22% to 27%. The risk for new postoperative hormonal deficiencies was 15%. Postoperative relieve of visual field and visual acuity deficiencies was seen in 94 (86%) and 73 (81%) patients, respectively.

Conclusion: Judged by long-term follow-ups of >200 nonfunctioning/functioning pituitary adenomas, the use of low-field iMRI in transsphenoidal surgery increases resection rates and sustainably influences outcomes.