Transsphenoidal resection of sellar tumors using high-field intraoperative magnetic resonance imaging

Abstract

There has been increasing experience in the utilization of intraoperative magnetic resonance imaging (iMRI) for intracranial surgery. Despite this trend, only a few U.S centers have examined the use of this technology for transsphenoidal resection of tumors of the sella. We present the largest series in North America examining the role of iMRI for pituitary adenoma resection. We retrospectively reviewed our institutional experience of 59-patients who underwent transsphenoidal procedures for sellar and suprasellar tumors with iMRI guidance. Of these, 52 patients had a histological diagnosis of pituitary adenoma. The technical results of this subgroup were examined. A 1.5-T iMRI was integrated with the BrainLAB (Feldkirchen, Germany) neuronavigation system. The majority (94%) of tumors in our series were macroadenomas. Seventeen percent of tumors were confined to the sella, 49% had suprasellar extensions without involvement of the cavernous sinus, 34% had frank cavernous sinus invasion. All patients underwent at least one iMRI, and 19% required one or more additional sets of intraoperative imaging. In 58% of patients, iMRI led to the surgeon attempting more resection. A gross total resection was obtained in 67% of the patients with planned total resections. There was one case of permanent postoperative diabetes insipidus and no other instances of new hormone replacement. In summary, iMRI was most useful for tumors of the sella with and without suprasellar extension where the information from the iMRI extended the complete resection rate from 40 to 72% and 55 to 88%, respectively. As one would expect, it did not substantially increase the rate of resection of tumors with cavernous sinus invasion. Overall, iMRI was particularly useful in guiding resection safely, aiding in clinical decision making, and allowing identification and preservation of the pituitary stalk and normal pituitary gland. Limitations of the iMRI include a need for additional personnel and training as well as additional operative time, which diminishes over time as personnel learn to optimize workflow efficiency. Additional costs are mitigated in part by using the iMRI as an immediate postoperative scan. Other data emerging from our experience suggest that preservation of normal gland and thus avoidance of hypopituitarism may be improved by iMRI use, but longer follow-up periods are required to test this conclusion. iMRI can detect unsuspected complications sooner than routine postoperative imaging, potentially leading to improved outcomes. However, larger studies are needed.

Keywords: Intraoperative MRI; pituitary; transsphenoidal.

Figure 1

Flow diagram depicting the resection algorithm with the intraoperative magnetic resonance imaging information.

Figure 2

Examples of intraoperative magnetic resonance imaging–aided sellar tumor resections of microadenoma. Coronal T1-weighted postgadolinium magnetic resonance images obtained preoperatively (A) and intraoperatively (B) in a patient with Cushing's disease. Two suspected microadenomas are visible on either side of the sella (arrows). Intraoperative scans confirmed resection of both lesions. The patient made a complete endocrinologic recovery after the procedure with resolution of her preoperative clinical symptoms.

Figure 3

Example of use of intraoperative magnetic resonance imaging (iMRI) to identify normal gland intraoperatively. (A) Preoperative magnetic resonance coronal T1-weighted postgadolinium injection in a patient with a large macroadenoma with no discernable normal gland. Once the majority of the resection was complete, iMRI (B) was used to distinguish remaining tumor (dashed white arrow) from normal gland (black arrow). White solid arrow identifies the pituitary stalk with right inferior normal enhancing gland as well as visualization of the optic chiasm, all of which allows safer tumor resection. Postoperative scan (C) shows the patient had a gross total resection with an intact stalk (white arrow) and normal gland (black arrow). The patient had normal pituitary function postoperatively.