This article provides an overview of intraoperative MRI (iMRI) use in transphenoidal surgery (TSS) for pituitary tumours. Traditionally imaging of the surgical field during surgery involves intraoperative fluoroscopic imaging or neuronavigation which help to avoid injury to critical structures but are not useful for monitoring extent of resection. Remission rates vary but a recent meta-analysis found mean rates of 68.8% for prolactinomas, 47.3% for non-functioning adenoma, 61.2% for growth hormone-secreting adenomas and 71.3% for corticotrophin secreting adenoma tumours. The authors suggest the following three challenges to improve remission rates after pituitary surgery: visibility of small tumours; visualisation of true extent of large tumours; and visualisation of tumour invasion. The authors summarised the findings of multiple studies into iMRI use in both microscope and endoscope use. The studies have a variety of field strengths, the first studies utilising low-field strength and later studies high-field which improve the resolution of resulting images. In addition, there are variable magnet and room configurations.

Most studies report that the primary benefit of iMRI lies in detection of tumour residuals following maximal resection with conventional technique. This can improve the rate of gross total resection (by 15% to 40%) and / or chemical remission (5% to 19%).

iMRI can be useful in detection of haematoma within the surgical field but appears currently to have limited detection of microadenoma. The study highlights some issues with safety, namely, extension of operating time by approximately two hours and the interpretation of intraoperative images can be challenging leading to false positive readings. This study highlights use of iMRI in pituitary surgery as an option with future direction in detection of microadenomas causing Cushing disease by improving spatial resolution and an increase in signal-to-noise ratio, which is offset by increasing expense.

iMRI during transphenoidal surgery.
Chittiboina P.
NEUROSURGERY CLINICS OF NORTH AMERICA
2017;28:499-512.
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CONTRIBUTOR
Aaron SJ Ferguson

Department of Otolaryngology, Ninewells Hospital, UK.

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