Implementation of a low field intraoperative MRI (PoleStarTM N20) during surgery for pituitary adenomas

Objectives: To report the results of a new compact intraoperative low- field strength magnetic resonance imaging (iMRI) system in terms of resection control during surgery for pituitary adenomas.

Methods: 24 patients underwent microsurgical resection of a pituitary adenoma (PA) (1 micro-, 23 macroadenomas; 6 functioning PA [4 GH-, 1 ACTH-, 1 PROL), 18 nonfunctioning PA]) using the PoleStarTM N20 0.15 T- system (Medtronic). According to preoperative 1.5T MRI patients were divided into two groups (intended complete [n=16] and incomplete resection due invasion of the cavernous sinus [n=8]). All tumors were operated via a transnasal transphenoidal approach. When the surgeon judged the resection as complete or when the resection goal was achieved an iMRI- scan was done (coronar T1- weighted sequences [±gadolinium]). In cases of accessible tumor remnants surgery was continued until either intended resection was achieved or further removal of residual tumor was impossible. Clinical and MRI (1.5T±Gd) follow up was routinely performed 3 months after surgery, which was available in 18 patients.

Results: In all patients appropriate iMRI images could be obtained and adequate decompression of the optic pathway was documented. iMRI resection control showed residual tumor leading to further resection in 7 patients (2 patients with intended complete an 4 in with intended incomplete resection). Although residual tumor was detected in 1 patient further resection was impossible due to the adherent capsule. Thus intended resection was achieved in 23 (95%) patients. In 1 patient with GH- secreting tumor the interpretation of iMRI showed questionable residual intrasellar tumor, but only minor tumor remnants could be removed. In this patient F/u MRI showed a small intrasellar residual tumor, leading to a second operation. For all other patients iMRI showed good correlation to the 3 months 1.5 T MRI F/u.

Conclusions: The 0.15T iMRI is a valuable adjunct for surgery of pituitary adenomas to verify residual tumor and the iMRI has a good correlation to the 3 months follow up 1.5T MRI.