Implementation of intraoperative magnetic resonance imaging (iMRI) has been shown to optimize the extent of resection and safety of brain tumor surgery. In addition, iMRI can help account for the phenomenon of brain shift and can help to detect complications earlier than routine postoperative imaging, which can potentially improve patient outcome.
Intraoperative MRI is considered the gold standard among all intraoperative imaging technologies currently available. Its main indication is in the intraoperative detection of residual disease during tumour resections.
Intraoperative magnetic resonance imaging (iMRI) is an effective and proven tool in transsphenoidal endoscopic surgery. However, image interpretation is not always easy and can be hindered by the presence of blood, tumor remains or the displacement of surrounding structures.
Jiménez et al present a novel technique based on using intrasellar ballons to reduce these difficulties and facilitate the surgeon’s intraoperative assessment by iMRI.
Noise of unknown origin
Low magnetic field iMRI devices may produce low-quality images due to nonideal imaging conditions in the operating room and additional noise of unknown origin.
Unbiased nonlocal means filter for iMRI de-noising proved very useful for image quality enhancement and assistance in the interpretation of iMR images 1).
The higher signal-to-noise ratio offered by 3 Tesla (T) iMRI compared with lower field strength systems is particularly advantageous.
To maximize efficiency, iMRI sequences can be tailored to particular types of tumors and procedures, including nonenhancing brain tumor surgery, enhancing brain tumor surgery, transsphenoidal pituitary tumor surgery, and laser ablation. Unique imaging findings on iMRI include the presence of surgically induced enhancement, which can be a potential confounder for residual enhancing tumor, and hyperacute hemorrhage, which tends to have intermediate signal on T1-weighted sequences and high signal on T2-weighted sequences due to the presence of oxyhemoglobin. MR compatibility and radiofrequency shielding pose particularly stringent technical constraints at 3T and influence the design and usage of the surgical suite with iMRI 2).
Intraoperative magnetic resonance imaging (iMRI) and functional neuronavigation may help maximize tumor resection, minimize language deficits in patients with gliomas involving language areas, and improve survival time for patients with glioblastomas 3).
The Medline, PubMed, Cochrane, Google Scholar databases were searched until September 26th, 2015 Randomized controlled trials (RCTs), two-arm prospective studies, retrospective studies in patients with glioblastoma/glioma who had received surgical treatment were included.
The primary outcome measures were the extent of tumor resection and tumor size reduction for using iMRI-guided or conventional neuronavigation-guided neurosurgery. Secondary outcomes included impact of surgery on the 6-month progression-free survival (PFS) and 12-month overall survival (OS) rates and surgical duration were also studied.
They found that iMRI was associated with greater rate of gross total resection (rGTR) compared with conventional neuronavigation procedures (3.16, 95% confidence interval [CI] 2.07-4.83, P < 0.001). We found no difference between the two neuronavigation approaches in extent of resection (EOR), tumor size reduction, or time required for surgery (P values ≥0.065). Intraoperative MRI was associated with a higher rate of progression-free survival (PFS) compared with conventional neuronavigation (odds ratio, 1.84; 95% CI of 1.15 to 2.95; P = 0.012), but the rate of overall survival (OS) between groups was similar (P = 0.799). Limitations of the study included the fact that data from non-RCTs were used, the small study population, and heterogeneity of outcomes across studies.
The findings indicate that iMRI more frequently resulted in more complete resections leading to improved PFS in patients with malignant gliomas 4).
In 300 consecutive patients, three sequential groups (groups A, B, C; n=100 each) were compared with respect to time management, complications and technical difficulties to assess improvement in these parameters with experience.
Raheja et al observed a reduction in the number of technical difficulties (p<0.001), time to induction (p<0.001) and total anesthesia time (p=0.007) in sequential groups. IOMRI was performed for neuronavigation guidance (n=252) and intraoperative validation of extent of resection (EOR; n=67). Performing IOMRI increased the EOR over and beyond the primary surgical attempt in 20.5% (29/141) and 18% (11/61) of patients undergoing glioma and pituitary surgery, respectively. Overall, EOR improved in 59.7% of patients undergoing IOMRI (40/67). Intraoperative tractography and real time navigation using re-uploaded IOMRI images (accounting for brain shift) helps in intraoperative planning to reduce complications. IOMRI is an asset to neurosurgeons, helping to augment the EOR, especially in glioma and pituitary surgery, with no significant increase in morbidity to the patient 5).
Brell et al. retrospectively reviewed the first 21 patients operated on the aid of this technology. Maximal safe resection was the surgical goal in all cases. Surgeries were performed using conventional instrumentation and the required assistance in each case.
The mean number of intraoperative studies was 2.3 per procedure (range: 2 to 4). Intraoperative studies proved that the surgical goal had been achieved in 15 patients (71.4%), and detected residual tumour in 6 cases (28.5%). After comparing the last intraoperative image and the postoperative study, 2 cases (9.5%) were considered as “false negatives”.
Intraoperative MRI is a safe, reliable and useful tool for guided resection of brain tumours. Low-field devices provide images of sufficient quality at a lower cost; therefore their universalisation seems feasible 6).
Giordano et al. describe two explicative cases including the setup, positioning, and the complete workflow of the surgical approach with intraoperative imaging. Even if the configuration of iopMRI equipment was originally designed for cranial surgery, they have demonstrated the feasibility of cervical intramedullary glioma resection with the aid of high-field iopMRI. This tool was extremely useful to evaluate the extent of tumor removal and to obtain a higher resection rate, but still need some enhancement in the configuration of the headrest coil and surgical table to allow better patient positioning 7).