Lows and highs: 15 years of development in intraoperative magnetic resonance imaging

Optimization of tumor resection with intra-operative magnetic resonance imaging

Intra-operative MRI (ioMRI) may be used to optimize tumor resection. Utilization of this technology allows for the removal of residual tumor mass following initial tumor removal, maximizing the extent of resection. This, in turn, has been shown to lead to improved outcomes. Individual studies have examined the impact of ioMRI on the rate of extended resection, but a comprehensive review of this topic is needed. A literature review of the MEDLINE, EMBASE, CENTRAL, and Google Scholar databases revealed 12 eligible studies. This included 804 primary operations and 238 extended resections based on ioMRI findings. Use of ioMRI led to extended tumor resection in 13.3-54.8% of patients (mean 37.3%). Stratification by tumor type showed additional resection occurred, on average, in 39.1% of glioma resections (range 13.3-70.0%), 23.5% of pituitary tumor resections (range 13.3-33.7%), and 35.0% of nonspecific tumor resections (range 17.5-40%). Tumor type (glioma vs. pituitary) did not significantly influence the rate of further excision following ioMRI (p=0.309). There was no difference in secondary resection rate between studies limited to pediatric patients and those including adults (p=0.646). Thus, the use of intra-operative MRI frequently results in further resection of tumors. It is primarily used for the resection of gliomas and pituitary tumors. Tumor type does not appear to be a significant contributing factor to the rate of secondary tumor removal. Limited evidence suggests that extended resection may translate into improved clinical outcomes and mortality rates. However, results have not been unanimous, while clinical effect sizes have often been modest.

Combining 5-Aminolevulinic Acid Fluorescence and Intraoperative Magnetic Resonance Imaging in Glioblastoma Surgery

BACKGROUND:

Glioblastoma resection guided by 5-aminolevulinic acid (5-ALA) fluorescence and intraoperative magnetic resonance imaging (iMRI) may improve surgical results and prolong survival.

OBJECTIVE:

To evaluate 5-ALA fluorescence combined with subsequent low-field iMRI for resection control in glioblastoma surgery.

METHODS:

Fourteen patients with suspected glioblastoma suitable for complete resection of contrast-enhancing portions were enrolled. The surgery was carried out using 5-ALA–induced fluorescence and frameless navigation. Areas suspicious for tumor underwent biopsy. After complete resection of fluorescent tissue, low-field iMRI was performed. Areas suspicious for tumor remnant underwent biopsy under navigation guidance and were resected. The histological analysis was blinded.

RESULTS:

In 13 of 14 cases, the diagnosis was glioblastoma multiforme. One lymphoma and 1 case without fluorescence were excluded. In 11 of 12 operations, residual contrast enhancement on iMRI was found after complete resection of 5-ALA fluorescent tissue. In 1 case, the iMRI enhancement was in an eloquent area and did not undergo a biopsy. The 28 biopsies of areas suspicious for tumor on iMRI in the remaining 10 cases showed tumor in 39.3%, infiltration zone in 25%, reactive central nervous system tissue in 32.1%, and normal brain in 3.6%. Ninety-three fluorescent and 24 non-fluorescent tissue samples collected before iMRI contained tumor in 95.7% and 87.5%, respectively.

CONCLUSION:

5-ALA fluorescence–guided resection may leave some glioblastoma tissue undetected. MRI might detect areas suspicious for tumor even after complete resection of all fluorescent tissue; however, due to the limited accuracy of iMRI in predicting tumor remnant (64.3%), resection of this tissue has to be considered with caution in eloquent regions.

Determining the utility of intraoperative magnetic resonance imaging for transsphenoidal surgery: a retrospective study

OBJECT

Intraoperative MRI (iMRI) provides updated information for neuronavigational purposes and assessments on the status of resection during transsphenoidal surgery (TSS). The high-field technique additionally provides information about vascular structures at risk and precise information about extrasellar residual tumor, making it readily available during the procedure. The imaging, however, extends the duration of surgery. To evaluate the benefit of this technique, the authors conducted a retrospective study to compare postoperative outcome and residual tumor in patients who underwent conventional microsurgical TSS with and without iMRI.

METHODS

A total of 143 patients were assessed. A cohort of 67 patients who had undergone surgery before introduction of iMRI was compared with 76 patients who had undergone surgery since iMRI became routine in TSS at the authors' institution. Residual tumor, complications, hormone dependency, biochemical remission rates, and improvement of vision were assessed at 6-month follow-up. A volumetric evaluation of residual tumor was performed in cases of parasellar tumor extension.

RESULTS

The majority of patients in both groups suffered from nonfunctioning pituitary adenomas. At the 6-month follow-up assessment, vision improved in 31% of patients who underwent iMRI-assisted surgery versus 23% in the conventional group. One instance of postoperative intrasellar bleeding was found in the conventional group. No major complications were found in the iMRI group. Minor complications were seen in 9% of patients in the iMRI group and in 5% of those in the conventional group. No differences between groups were found for hormone dependency and biochemical remission rates. Time of surgery was significantly lower in the conventional treatment group. Overall a residual tumor was found after surgery in 35% of the iMRI group, and 41% of the conventional surgery group harbored a residual tumor. Total resection was achieved as intended significantly more often in the iMRI group (91%) than in the conventional group (73%) (p < 0.034). Patients with a planned subtotal resection showed higher mean volumes of residual tumor in the conventional group. There was a significantly lower incidence of intrasellar tumor remnants in the iMRI group than in the conventional group. Progression-free survival after 30 months was higher according to Kaplan-Meier analysis with the use of iMRI, but a statistically significant difference could not be shown.

CONCLUSIONS

The use of high-field iMRI leads to a significantly higher rate of complete resection. In parasellar tumors a lower residual volume and a significantly lower rate of intrasellar tumor remnants were shown with the technique. So far, long-term follow-up is limited for iMRI. However, after 2 years Kaplan-Meier analyses show a distinctly higher progression-free survival in the iMRI group. No significant benefit of iMRI was found for biochemical remission rates and improvement of vision. Even though the surgical time was longer with the adjunct use of iMRI, it did not increase the complication rate significantly. The authors therefore recommend routine use of high-field iMRI for pituitary surgery, if this technique is available at the particular center.

Improving on-time start for iMRI neurosurgeries

BACKGROUND

In the Singapore General Hospital, intraoperative MRI (iMRI) neurosurgery is a multi-disciplinary process that involves staff from multiple departments. However, a baseline analysis showed that only 10.5% of iMRI neurosurgeries start on time, resulting in unnecessary waste of resources. The project aimed to improve the percentage of on-time start iMRI neurosurgeries to 100% within nine months.

MATERIALS AND METHODS

Clinical Practice Improvement methodology was used. The project involves four phases: Diagnostic, in which a baseline analysis is conducted; Intervention, in which problem areas are identified; Implementation, in which potential solutions are implemented; and sustaining, in which strategies to sustain gains are discussed.

RESULTS

The percentage of on-time start cases gradually increased to 100% in eight months, and was sustained above 85% in the following five months.

CONCLUSION

This project serves as a successful demonstration of how quality improvement can be effected in a complex, multidisciplinary workflow, which is the norm for many hospital procedures.

Intraoperative image guidance in neurosurgery: development, current indications, and future trends

Introduction. As minimally invasive surgery becomes the standard of care in neurosurgery, it is imperative that surgeons become skilled in the use of image-guided techniques. The development of image-guided neurosurgery represents a substantial improvement in the microsurgical treatment of tumors, vascular malformations, and other intracranial lesions. Objective. There have been numerous advances in neurosurgery which have aided the neurosurgeon to achieve accurate removal of pathological tissue with minimal disruption of surrounding healthy neuronal matter including the development of microsurgical, endoscopic, and endovascular techniques. Neuronavigation systems and intraoperative imaging should improve success in cranial neurosurgery. Additional functional imaging modalities such as PET, SPECT, DTI (for fiber tracking), and fMRI can now be used in order to reduce neurological deficits resulting from surgery; however the positive long-term effect remains questionable for many indications. Method. PubMed database search using the search term "image guided neurosurgery." More than 1400 articles were published during the last 25 years. The abstracts were scanned for prospective comparative trials. Results and Conclusion. 14 comparative trials are published. To date significant data amount show advantages in intraoperative accuracy influencing the perioperative morbidity and long-term outcome only for cerebral glioma surgery.