First-in-Human Intraoperative MRI Coil for High-Resolution Imaging during Transsphenoidal Surgery

Introduction: For pituitary adenomas, including nonfunctioning pituitary adenomas and hormone secreting adenomas causing Cushing’s disease (CD) or acromegaly, transsphenoidal surgery (TSS) remains the therapy of first choice. In modern series, failure rates following TSS range from 20 to 80% with recurrences in up to 7 to 35% cases. Surgical failures and recurrences are particularly challenging for hormone-secreting adenomas. The causes of surgical failures include inability to visualize small adenomas, the true extent of large adenomas, or invasion of parasellar structures. Surgeons have historically utilized ultrasonography, intraoperative MRI (iMRI), or Doppler ultrasound as surgical adjuncts with limited success. iMRI potentially allows significant improvements in visualization during surgery with visualization proportional to magnetic field strength of the iMRI magnet. However, increasing the magnetic field strength over 3 Tesla is expensive and is currently impractical for iMRI studies. To improve on the imaging resolution of the pituitary gland and the parasellar structures, we developed an intraoperative coil that can be placed within the sphenoid sinus (the endosphenoidal coil [ESC]) during sublabial TSS. Here, we assessed the feasibility of using the ESC as a surgical adjunct during TSS.

Methods: We designed a first-in-human interventional trial (NCT03678389) to evaluate the feasibility of ESC use during TSS at the NIH Clinical Center in Bethesda. Patients >18 years of age with a known or suspected pituitary tumor that requires surgical resection through a transsphenoidal approach are included. Children and patients with unfavorable anatomy are excluded. Primary outcome is to test the feasibility of using ESC as a surgical adjunct. Feasibility criterion is met if ESC use adds less than 90 minutes to the standard-of-care procedure. A hard stop for all research procedures occurs at 120 minutes after which only clinical standard-of-care procedures are allowed. The safety outcome measure is to evaluate whether ESC (images 1 and 2 below) causes local trauma, bleeding, burns, or other unanticipated safety issues.

Results: Since initiating recruitment in June 2019, we have enrolled two patients. For both patients, ESC insertion and imaging were performed under sterile conditions following initial approach to the sphenoid sinus. For patient 1, we successfully inserted the ESC and obtained clinically useful images in 110 minutes (failed to meet primary outcome criterion). For patient 2, we completed all research procedures including ESC insertion and imaging within 90 minutes (primary outcome measure met). In both cases, safety outcomes were met. We observed a significant improvement in the workflow during this period. The patients tolerated the procedures well and sustained no unanticipated adverse events.

Conclusion: So far, we find that it is safe and feasible to use ESC for intraoperative MRI imaging during sublabial TSS. The future use of this coil could allow visualizations of microadenomas, microscopic cavernous sinus invasion, or residual macroadenomas currently not visualized with standard techniques. (Images below are intraoperative MRI images obtained using the ESC, coronal slices through the sella.)

No conflict of interest has been declared by the author(s).