Use of intraoperative magnetic resonance imaging in tailored temporal lobe surgeries for epilepsy

Intraoperative use of low-field magnetic resonance imaging for brain tumors: A systematic review

Background

Low-field magnetic resonance imaging (LF-MRI) has become a valuable tool in the diagnosis of brain tumors due to its high spatial resolution and ability to acquire images in a short amount of time. However, the use of LF-MRI for intraoperative imaging during brain tumor surgeries has not been extensively studied. The aim of this systematic review is to investigate the impact of low-field intraoperative magnetic resonance imaging (LF-IMRI) on the duration of brain tumor surgery and the extent of tumor resection.

Methods

A comprehensive literature search was conducted using PubMed, Scopus, and Google Scholar from February 2000 to December 2022. The studies were selected based on the inclusion criteria and reviewed independently by two reviewers. The gathered information was organized and analyzed using Excel.

Results

Our review of 21 articles found that low-field intraoperative MRI (LF-IMRI) with a field below 0.3T was used in most of the studies, specifically 15 studies used 0.15T LF-IMRI. The T1-weighted sequence was the most frequently reported, and the average scanning time was 24.26 min. The majority of the studies reported a positive impact of LF-IMRI on the extent of tumor resection, with an increase ranging from 11% to 52.5%. Notably, there were no studies describing the use of ultra-low-field (ULF) intraoperative MRI.

Conclusion

The results of this systematic review will aid neurosurgeons and neuroradiologists in making informed decisions about the use of LF-MRI in brain tumor surgeries. Further, research is needed to fully understand the impact of LF-MRI in brain tumor surgeries and to optimize its use in the clinical setting. There is an opportunity to study the utility of ULF-MRI in brain tumor surgeries.

Intraoperative magnetic resonance imaging in epilepsy surgery: A systematic review and meta-analysis

This systematic review investigated the added value of intraoperative magnetic resonance imaging (iMRI)-guidance in epilepsy surgery, compared to conventional non-iMRI surgery, with respect to the rate of gross total resection (GTR), postoperative seizure freedom, neurological deficits, non-neurological complications and reoperations. A comprehensive literature search was conducted using Medline, Embase, PubMed, and Cochrane Reviews databases. Randomized control trials, case control or cohort studies, and surgical case series published from January 1993 to February 2021 that reported on iMRI-guided epilepsy surgery outcomes for either adults or children were eligible for inclusion. Studies comparing iMRI-guided epilepsy surgery to non-iMRI surgery controls were selected for meta-analysis using random-effects models. Forty-two studies matched the selection criteria and were used for qualitative synthesis and ten of these were suitable for meta-analysis. Overall, studies included various 0.2-3.0 Tesla iMRI systems, contained small numbers with heterogenous clinical characteristics, utilized subjective GTR reporting, and had variable follow-up durations. Meta-analysis demonstrated that the use of iMRI-guidance led to statistically significant higher rates of GTR (RR = 1.31 [95% CI = 1.10-1.57]) and seizure freedom (RR = 1.44 [95% CI = 1.12-1.84]), but this was undermined by moderate to significant statistical heterogeneity between studies (I² = 55% and I² = 71% respectively). Currently, there is only level III-2 evidence supporting the use of iMRI-guidance over conventional non-iMRI epilepsy surgery, with respect to the studied outcomes.

Operative variations in temporal lobe epilepsy surgery and seizure and memory outcome in 226 patients suffering from hippocampal sclerosis

Objective: The aim of this retrospective cohort study was to assess seizure and memory outcomes following temporal lobe surgery in patients suffering from medically refractory temporal lobe epilepsy (TLE) and hippocampal sclerosis (HS).Methods: A retrospective monocentric data analysis was performed in consecutive patients who were operated on during 2002-2018. In the first decennium, standard temporal lobe resections (TLR) were predominately performed, and later, antero-temporal lobe resections (ATLR) were mainly performed. Seizure and memory outcomes over time were assessed according to ILAE/Engel classification and the Berlin Amnesia Test (BTA), respectively.Results: Altogether, 231 surgeries were performed on 226 patients (mean age, 40 years [range, 10-68 years]; male: female, 1:1.4; mean seizure duration, 25 years; and mean follow-up duration, 4.75 years [range, 1-16]). Recently, outcomes of 78.3% of the patients in the total cohort were classified as Engel class I, with 54.9% of patients being completely seizure free. The recent cohort of ATLR since 2012 showed significant more completely seizure-free patients than before 2012 (Engel IA 46.6% versus 67.7%, p < 0.0025, χ²), although the Kaplan Meier analysis of all patients favors TLR for better seizure outcome (61% ATLR vs 73% TLR seizure free after 5 yrs, log rank p < 0.001). Verbal memory improved significantly in non-dominant patients. Minor neurological complications were noted (permanent severe complications, 0.4%; temporary severe complications, 4.8%).Conclusion: Significant improvements in seizure and memory outcomes were observed over time, with surgical technique and seizure duration as important prognostic factors. Early admittance for surgery may favor an excellent seizure outcome in patients undergoing temporal lobe resection for HS.

Utility and pitfalls of high field 3 tesla intraoperative MRI in neurosurgery: A single centre experience of 100 cases

Objective

In India, few centers are using 1.5 Tesla intraoperative MRI systems. We are using a 3 Tesla iMRI system. We share our initial experience of 3T iMRI in neurosurgical procedures with evaluation of its utility and pitfalls.

Methods

A prospective observational study conducted between August 2017 to July 2018 at Yashoda Hospital, Secunderabad. All patients undergoing iMRI guided resection of intracranial SOL were included.

Results

First 100 patients with various intracranial SOLs were included. The mean time required in shifting and image acquisition was 85.6 minutes in first 20 cases which was reduced to 37.4 minutes in next the next cases. Primary GTR was achieved in 44% cases, and residues were detected in 56%, secondary GTR was achieved in 37% cases, and surgery was discontinued in 19%. Maximum residues were detected in intraaxial sols and pituitary macroadenomas. No major iMRI associated complications were seen, minor issues involving transportation and minor contact burns were seen in 4 cases, insignificant anesthetic procedure related complications in 19 cases.

Conclusion

As per our experience iMRI is an excellent tool to guide and improve the extent of safe resection by 37% in brain tumor surgeries. Good image quality, less time for image acquisition was observed advantages of 3T system. iMRI success depends on multidepartment coordinated teamwork and multiple iterations of the process to smoothen the workflow.

Ultrasonographic features of focal cortical dysplasia and their relevance for epilepsy surgery

OBJECTIVE Surgery has proven to be the best therapeutic option for drug-refractory cases of focal cortical dysplasia (FCD)-associated epilepsy. Seizure outcome primarily depends on the completeness of resection, rendering the intraoperative FCD identification and delineation particularly important. This study aims to assess the diagnostic yield of intraoperative ultrasound (IOUS) in surgery for FCD-associated drug-refractory epilepsy. METHODS The authors prospectively enrolled 15 consecutive patients with drug-refractory epilepsy who underwent an IOUS-assisted microsurgical resection of a radiologically suspected FCD between January 2013 and July 2016. The findings of IOUS were compared with those of presurgical MRI postprocessing and the sonographic characteristics were analyzed in relation to the histopathological findings. The authors investigated the added value of IOUS in achieving completeness of resection and improving postsurgical seizure outcome. RESULTS The neurosurgeon was able to identify the dysplastic tissue by IOUS in all cases. The visualization of FCD type I was more challenging compared to FCD II and the demarcation of its borders was less clear. Postsurgical MRI showed residual dysplasia in 2 of the 3 patients with FCD type I. In all FCD type II cases, IOUS allowed for a clear intraoperative visualization and demarcation, strongly correlating with presurgical MRI postprocessing. Postsurgical MRI confirmed complete resection in all FCD type II cases. Sonographic features correlated with the histopathological classification of dysplasia (sonographic abnormalities increase continuously in the following order: FCD IA/IB, FCD IC, FCD IIA, FCD IIB). In 1 patient with IOUS features atypical for FCD, histopathological investigation showed nonspecific gliosis. CONCLUSIONS Morphological features of FCD, as identified by IOUS, correlate well with advanced presurgical imaging. The resolution of IOUS was superior to MRI in all FCD types. The appreciation of distinct sonographic features on IOUS allows the intraoperative differentiation between FCD and non-FCD lesions as well as the discrimination of different histological subtypes of FCD. Sonographic demarcation depends on the underlying degree of dysplasia. IOUS allows for more tailored resections by facilitating the delineation of the dysplastic tissue.

Investigation of subdural electrode displacement in invasive epilepsy surgery workup using neuronavigation and intraoperative MRI

OBJECTIVES

One of the main obstacles of electrode implantation in epilepsy surgery is the electrode shift between implantation and the day of explantation. We evaluated this possible electrode displacement using intraoperative MRI (iopMRI) data and CT/MRI reconstruction.

METHODS

Thirteen patients (nine female, four male, median age 26 ± 9.4 years) suffering from drug-resistant epilepsy were examined. After implantation, the position of subdural electrodes was evaluated by 3.0 T-MRI and thin-slice CCT for 3D reconstruction. Localization of electrodes was performed with the volume-rendering technique. Post-implantation and pre-explantation 1.5 T-iopMRI scans were coregistered with the 3D reconstructions to determine the extent of electrode dislocation.

RESULTS

Intraoperative MRI at the time of explantation revealed a relevant electrode shift in one patient (8%) of 10 mm. Median electrode displacement was 1.7 ± 2.6 mm with a coregistration error of 1.9 ± 0.7 mm. The median accuracy of the neuronavigation system was 2.2 ± 0.9 mm. Six of twelve patients undergoing resective surgery were seizure free (Engel class 1A, median follow-up 37.5 ± 11.8 months).

CONCLUSION

Comparison of pre-explantation and post-implantation iopMRI scans with CT/MRI data using the volume-rendering technique resulted in an accurate placement of electrodes. In one patient with a considerable electrode dislocation, the surgical approach and extent was changed due to the detected electrode shift.

ABBREVIATIONS

ECoG: electrocorticography; EZ: epileptogenic zone; iEEG: invasive EEG; iopMRI: intraoperative MRI; MEG: magnetoencephalography; PET: positron emission tomography; SPECT: single photon emission computed tomography; 3D: three-dimensional.

Resective surgery for medically refractory epilepsy using intraoperative MRI and functional neuronavigation: the Erlangen experience of 415 patients

OBJECTIVE

Intraoperative overestimation of resection volume in epilepsy surgery is a well-known problem that can lead to an unfavorable seizure outcome. Intraoperative MRI (iMRI) combined with neuronavigation may help surgeons avoid this pitfall and facilitate visualization and targeting of sometimes ill-defined heterogeneous lesions or epileptogenic zones and may increase the number of complete resections and improve seizure outcome.

METHODS

To investigate this hypothesis, the authors conducted a retrospective clinical study of consecutive surgical procedures performed during a 10-year period for epilepsy in which they used neuronavigation combined with iMRI and functional imaging (functional MRI for speech and motor areas; diffusion tensor imaging for pyramidal, speech, and visual tracts; and magnetoencephalography and electrocorticography for spike detection). Altogether, there were 415 patients (192 female and 223 male, mean age 37.2 years; 41% left-sided lesions and 84.9% temporal epileptogenic zones). The mean preoperative duration of epilepsy was 17.5 years. The most common epilepsy-associated pathologies included hippocampal sclerosis (n = 146 [35.2%]), long-term epilepsy-associated tumor (LEAT) (n = 67 [16.1%]), cavernoma (n = 45 [10.8%]), focal cortical dysplasia (n = 31 [7.5%]), and epilepsy caused by scar tissue (n = 23 [5.5%]).

RESULTS

In 11.8% (n = 49) of the surgeries, an intraoperative second-look surgery (SLS) after incomplete resection verified by iMRI had to be performed. Of those incomplete resections, LEATs were involved most often (40.8% of intraoperative SLSs, 29.9% of patients with LEAT). In addition, 37.5% (6 of 16) of patients in the diffuse glioma group and 12.9% of the patients with focal cortical dysplasia underwent an SLS. Moreover, iMRI provided additional advantages during implantation of grid, strip, and depth electrodes and enabled intraoperative correction of electrode position in 13.0% (3 of 23) of the cases. Altogether, an excellent seizure outcome (Engel Class I) was found in 72.7% of the patients during a mean follow-up of 36 months (range 3 months to 10.8 years). The greatest likelihood of an Engel Class I outcome was found in patients with cavernoma (83.7%), hippocampal sclerosis (78.8%), and LEAT (75.8%). Operative revisions that resulted from infection occurred in 0.3% of the patients, from hematomas in 1.6%, and from hydrocephalus in 0.8%. Severe visual field defects were found in 5.2% of the patients, aphasia in 5.7%, and hemiparesis in 2.7%, and the total mortality rate was 0%.

CONCLUSIONS

Neuronavigation combined with iMRI was beneficial during surgical procedures for epilepsy and led to favorable seizure outcome with few specific complications. A significantly higher resection volume associated with a higher chance of favorable seizure outcome was found, especially in lesional epilepsy involving LEAT or diffuse glioma.

The role of intraoperative MRI in resective epilepsy surgery for peri-eloquent cortex cortical dysplasias and heterotopias in pediatric patients

OBJECTIVE

Previous studies have demonstrated that an important factor in seizure freedom following surgery for lesional epilepsy in the peri-eloquent cortex is completeness of resection. However, aggressive resection of epileptic tissue localized to this region must be balanced with the competing objective of retaining postoperative neurological functioning. The objective of this study was to investigate the role of intraoperative MRI (iMRI) as a complement to existing epilepsy protocol techniques and to compare rates of seizure freedom and neurological deficit in pediatric patients undergoing resection of perieloquent lesions.

METHODS

The authors retrospectively reviewed the medical records of pediatric patients who underwent resection of focal cortical dysplasia (FCD) or heterotopia localized to eloquent cortex regions at the Children's National Health System between March 2005 and August 2015. Patients were grouped into two categories depending on whether they underwent conventional resection (n = 18) or iMRI-assisted resection (n = 11). Patient records were reviewed for factors including demographics, length of hospitalization, postoperative seizure freedom, postoperative neurological deficit, and need for reoperation. Postsurgical seizure outcome was assessed at the last postoperative follow-up evaluation using the Engel Epilepsy Surgery Outcome Scale.

RESULTS

At the time of the last postoperative follow-up examination, 9 (82%) of the 11 patients in the iMRI resection group were seizure free (Engel Class I), compared with 7 (39%) of the 18 patients in the control resection group (p = 0.05). Ten (91%) of the 11 patients in the iMRI cohort achieved gross-total resection (GTR), compared with 8 (44%) of 18 patients in the conventional resection cohort (p = 0.02). One patient in the iMRI-assisted resection group underwent successful reoperation at a later date for residual dysplasia, compared with 7 patients in the conventional resection cohort (with 2/7 achieving complete resection). Four (36%) of the patients in the iMRI cohort developed postoperative neurological deficits, compared with 15 patients (83%) in the conventional resection cohort (p = 0.02).

CONCLUSIONS

These results suggest that in comparison with a conventional surgical protocol and technique for resection of epileptic lesions in peri-eloquent cortex, the incorporation of iMRI led to elevated rates of GTR and postoperative seizure freedom. Furthermore, this study suggests that iMRI-assisted surgeries are associated with a reduction in neurological deficits due to intraoperative damage of eloquent cortex.

Resection of cerebral gangliogliomas causing drug-resistant epilepsy: short- and long-term outcomes using intraoperative MRI and neuronavigation

OBJECT Cerebral gangliogliomas (GGs) are highly associated with intractable epilepsy. Incomplete resection due to proximity to eloquent brain regions or misinterpretation of the resection amount is a strong negative predictor for local tumor recurrence and persisting seizures. A potential method for dealing with this obstacle could be the application of intraoperative high-field MRI (iopMRI) combined with neuronavigation. METHODS Sixty-nine patients (31 female, 38 male; median age 28.5 ± 15.4 years) suffering from cerebral GGs were included in this retrospective study. Five patients received surgery twice in the observation period. In 48 of the 69 patients, 1.5-T iopMRI combined with neuronavigational guidance was used. Lesions close to eloquent brain areas were resected with the implementation of preoperative diffusion tensor imaging tractography and blood oxygenation level-dependent functional MRI (15 patients). RESULTS Overall, complete resection was accomplished in 60 of 69 surgical procedures (87%). Two patients underwent biopsy only, and in 7 patients, subtotal resection was accomplished because of proximity to critical brain areas. Excluding the 2 biopsies, complete resection using neuronavigation/iopMRI was documented in 33 of 46 cases (72%) by intraoperative imaging. Remnant tumor mass was identified intraoperatively in 13 of 46 patients (28%). After intraoperative second-look surgery, the authors improved the total resection rate by 9 patients (up to 91% [42 of 46]). Of 21 patients undergoing conventional surgery, 14 (67%) had complete resection without the use of iopMRI. Regarding epilepsy outcome, 42 of 60 patients with seizures (70%) became completely seizure free (Engel Class IA) after a median follow-up time of 55.5 ± 36.2 months. Neurological deficits were found temporarily in 1 (1.4%) patient and permanently in 4 (5.8%) patients. CONCLUSIONS Using iopMRI combined with neuronavigation in cerebral GG surgery, the authors raised the rate of complete resection in this series by 19%. Given the fact that total resection is a strong predictor of long-term seizure control, this technique may contribute to improved seizure outcome and reduced neurological morbidity.

Intraoperative MR Imaging in Neurosurgery

Intraoperative magnetic resonance imaging (iMRI) has dramatically expanded and nowadays presents state-of-the-art technique for image-guided neurosurgery, facilitating critical precision and effective surgical treatment of various brain pathologies. Imaging hardware providing basic imaging sequences as well as advanced MRI can be seamlessly integrated into routine surgical environments, which continuously leads to emerging indications for iMRI-assisted surgery. Besides the obvious intraoperative diagnostic yield, the initial clinical benefits have to be confirmed by future-controlled long-term studies.

Malformations of cortical development and neocortical focus

Developmental neocortical malformations resulting from abnormal neurogenesis, disturbances in programmed cell death, or neuronal migration disorders may cause a long-term hyperexcitability. Early generated Cajal-Retzius and subplate neurons play important roles in transient cortical circuits, and structural/functional disorders in early cortical development may induce persistent network disturbances and epileptic disorders. In particular, depolarizing GABAergic responses are important for the regulation of neurodevelopmental events, like neurogenesis or migration, while pathophysiological alterations in chloride homeostasis may cause epileptic activity. Although modern imaging techniques may provide an estimate of the structural lesion, the site and extent of the cortical malformation may not correlate with the epileptogenic zone. The neocortical focus may be surrounded by widespread molecular, structural, and functional disturbances, which are difficult to recognize with imaging technologies. However, modern imaging and electrophysiological techniques enable focused hypotheses of the neocortical epileptogenic zone, thus allowing more specific epilepsy surgery. Focal cortical malformation can be successfully removed with minimal rim, close to or even within eloquent cortex with a promising risk-benefit ratio.

Frameless stereotactic functional neuronavigation combined with intraoperative magnetic resonance imaging as a strategy in highly eloquent located tumors causing epilepsy

BACKGROUND

Intractable epilepsy due to tumors located in highly eloquent brain regions is often considered surgically inaccessible because of a high risk of postoperative neurological deterioration. Intraoperative MRI and functional navigation contribute to overcome this problem.

OBJECTIVES

To retrospectively investigate the long-term results and impact of functional neuronavigation and 1.5-tesla intraoperative MRI on patients who underwent surgery of tumors associated with epilepsy located close to or within eloquent brain areas.

METHODS

Nineteen patients (9 female, 10 male, mean age 41.4 ± 13.4 years, 11 low-grade and 8 high-grade glial tumors) were evaluated preoperatively using BOLD imaging, diffusion-tensor imaging tractography and magnetoencephalography. Functional data were implemented into neuronavigation in this multimodal approach.

RESULTS

In 14 of 19 patients (74%), complete resection was achieved, and in 5 patients significant tumor volume reduction was accomplished. Eight of 14 (57%) complete resections were achieved only by performing an intraoperative image update. Neurological deterioration was found permanently in 2 patients. After a mean follow-up of 43.8 ± 23.8 months, 15 patients (79%) became seizure free (Engel class Ia).

CONCLUSIONS

Despite the highly eloquent location of tumors causing intractable epilepsy, our multimodal approach led to complete resection in more than two-thirds of patients with an acceptable neurological morbidity and excellent long-term seizure control.

Epilepsy surgery, vision, and driving: what has surgery taught us and could modern imaging reduce the risk of visual deficits?

Up to 40% of patients with temporal lobe epilepsy (TLE) are refractory to medication. Surgery is an effective treatment but may cause new neurologic deficits including visual field deficits (VFDs). The ability to drive after surgery is a key goal, but a postoperative VFD precludes driving in 4-50% of patients even if seizure-free. VFDs are a consequence of damage to the most anterior portion of the optic radiation, Meyer's loop. Anatomic dissection reveals that the anterior extent of Meyer's loop is highly variable and may clothe the temporal horn, a key landmark entered during temporal lobe epilepsy surgery. Experience from surgery since the 1940s has shown that VFDs are common (48-100%) and that the degree of resection affects the frequency or severity of the deficit. The pseudowedge shape of the deficit has led to a revised retinotopic model of the organization of the optic radiation. Evidence suggests that the left optic radiation is more anterior and thus at greater risk. Alternative surgical approaches, such as selective amygdalo-hippocampectomy, may reduce this risk, but evidence is conflicting or lacking. The optic radiation can be delineated in vivo using diffusion tensor imaging tractography, which has been shown to be useful in predicting the postoperative VFDs and in surgical planning. These data are now being used for surgical guidance with the aim of reducing the severity of VFDs. Compensation for brain shift occurring during surgery can be performed using intraoperative magnetic resonance imaging (MRI), but the additional utility of this expensive technique remains unproven.

Intra-operative 3-T MRI for paediatric brain tumours: challenges and perspectives

MRI is the ideal modality for imaging intracranial tumours. Intraoperative MRI (ioMRI) makes it possible to obtain scans during a neurosurgical operation that can aid complete macroscopic tumour resection—a major prognostic factor in the majority of brain tumours in children. Intraoperative MRI can also help limit damage to normal brain tissue. It therefore has the potential to improve the survival of children with brain tumours and to minimise morbidity, including neurological deficits. The use of ioMRI is also likely to reduce the need for second look surgery, and may reduce the need for chemotherapy and radiotherapy. Highfield MRI systems provide better anatomical information and also enable effective utilisation of advanced MRI techniques such as perfusion imaging, diffusion tensor imaging, and magnetic resonance spectroscopy. However, high-field ioMRI facilities require substantial capital investment, and careful planning is required for optimal benefit. Safe ioMRI requires meticulous attention to detail and rigorous application of magnetic field safety precautions. Interpretation of ioMRI can be challenging and requires experience and understanding of artefacts that are common in the intra-operative setting.

Anesthetic concerns for pediatric patients in an intraoperative MRI suite

PURPOSE OF REVIEW

Intraoperative magnetic resonance imaging (iMRI) is an evolving technology used to provide precise intraoperative navigation during a variety of neurosurgical and other types of surgical procedures. Anesthesiologists need to be aware of the unique challenges created by this environment. Failure to recognize the differences between the diagnostic MRI environment and the iMRI environment can compromise the safety of the patient and operating room staff and present logistical problems.

RECENT FINDINGS

Recent surgical reports herald the uses and benefits of iMRI. However, there are a few in the anesthesia literature addressing the significant benefits and the anesthesia-specific issues this technology creates. We will review recent reports describing anesthetic care of patients in this environment as well as examine the recent surgical and radiologic literature as they relate to issues faced by anesthesiologists.

SUMMARY

We describe the design of different iMRI suites as well as provide a breakdown of both patient and equipment issues encountered by anesthesiologists practicing in this environment. Finally, we offer our ongoing experience in this environment and provide suggestions to optimize patient outcomes.

Implementation and preliminary clinical experience with the use of ceiling mounted mobile high field intraoperative magnetic resonance imaging between two operating rooms

OBJECTIVE

Intraoperative magnetic resonance imaging (ioMRI) provides immediate feedback and quality assurance enabling the neurosurgeon to improve the quality of a range of neurosurgical procedures. Implementation of ioMRI is a complex and costly process. We describe our preliminary 16 months experience with the integration of an IMRIS movable ceiling mounted high field (1.5 T) ioMRI setup with two operating rooms.

METHODS

Aspects of implementation of our ioMRI and our initial 16 months of clinical experience in 180 consecutive patients were reviewed.

RESULTS

The installation of a ceiling mounted movable ioMRI between two operating rooms was completed in April 2008 at Barnes-Jewish Hospital in St. Louis. Experience with 180 neurosurgical cases (M:F-100:80, age range 1-79 years, 71 gliomas, 57 pituitary adenomas, 9 metastases, 11 other tumor cases, 4 Chiari decompressions, 6 epilepsy resections and 22 other miscellaneous procedures) demonstrated that this device effectively provided high quality real-time intraoperative imaging. In 74 of all 180 cases (41%) and in 54% of glioma resections, the surgeon modified the procedure based upon the ioMRI. Ninety-three percent of ioMRI glioma cases achieved gross/near total resection compared to 65% of non ioMRI glioma cases in this time frame.

CONCLUSION

A movable high field strength ioMRI can be safely integrated between two neurosurgical operating rooms. This strategy leads to modification of the surgical procedure in a significant number of cases, particularly for glioma surgery. Long-term follow up is needed to evaluate the clinical and financial impact of this technology in the field of neurosurgery.

Image guidance and neuromonitoring in neurosurgery

INTRODUCTION

The localization of tumors and epileptogenic foci within the somatosensory or language cortex of the brain of a child poses unique neurosurgical challenges. In the past, lesions in these regions were not treated aggressively for fear of inducing neurological deficits. As a result, while function may have been preserved, the underlying disease may not have been optimally treated, and repeat neurosurgical procedures were frequently required. Today, with the advent of preoperative brain mapping, image guidance or neuronavigation, and intraoperative monitoring, peri-Rolandic and language cortex lesions can be approached directly and definitively with a high degree of confidence that neurosurgical function will be maintained.

METHODS AND RESULTS

The preoperative brain maps can now be achieved with magnetic resonance imaging (MRI), functional MRI, magnetoencephalography, and diffusion tensor imaging. Image guidance systems have improved significantly and include the use of the intraoperative MRI. Somatosensory, motor, and brainstem auditory-evoked potentials are used as standard neuromonitoring techniques in many centers around the world. Added to this now is the use of continuous train-of-five monitoring of the integrity of the corticospinal tract while operating in the peri-Rolandic region.

CONCLUSION

We are in an era where continued advancements can be expected in mapping additional pathways such as visual, memory, and hearing pathways. With these new advances, neurosurgeons can expect to significantly improve their surgical outcomes further.

Optimizing costs of intraoperative magnetic resonance imaging. A series of 29 glioma cases

PURPOSE

The goal of this study was to develop a method to reduce the costs of intraoperative high-field magnet resonance imaging (iMRI). The results of a series of 29 gliomas removed with this technique are presented.

METHODS

A series of 29 patients with brain gliomas were operated on using a low-cost method of high-field intraoperative MRI (Signa 1.5 T. MR Excite, GE Inc.). The patients were transported during surgery to the neuroradiological department through a specially located lift in order to perform the intraoperative examinations ("outside iMRI"). The time required for the procedure as well as the possible related complications, such as infection, were analyzed.

RESULTS

After studying the intraoperative images, additional tumor resection was needed in 12 of the 29 patients. The median time required to perform the iMRI was 25 min. There was no infection or other complications related to the procedure in this series.

CONCLUSIONS

This method offers all clinical advantages of high-field iMRI inside of the operating room, with very low costs and additional advantage of integrating the neurosurgical/ neuroradiological teams. This strategy will give an alternative to several neurosurgical departments in the world to perform high-quality iMRI at very low cost.

Application of intraoperative high-field magnetic resonance imaging in pediatric neurosurgery

OBJECT

Over the past decade, the use of intraoperative MR (iMR) imaging in the pediatric neurosurgical population has become increasingly accepted as an innovative and important neurosurgical tool. The authors summarize their experience using a mobile 1.5-T iMR imaging unit with integrated neuronavigation with the goal of identifying procedures and/or pathologies in which the application of this technology changed the course of surgery or modified the operative strategy.

METHODS

A database has been prospectively maintained for this patient population. The authors reviewed the hospital charts and imaging results for all patients in the database. This review revealed 105 neurosurgical procedures performed in 98 children (49 male and 49 female) between March 1998 and April 2008. Intradissection (ID) and/or quality assurance images were obtained at the discretion of the surgeon.

RESULTS

The median age at surgery was 12 years (4 months-18 years). One hundred intracranial and 5 spinal procedures were performed; 22 of these procedures were performed for recurrent pathology. Surgical planning scans were obtained for 102 procedures, and neuronavigation was used in 93 patients. The greatest impact of iMR imaging was apparent in the 55 procedures to resect neoplastic lesions; ID scans were obtained in 49 of these procedures. Further surgery was performed in 49% of the procedures during which ID scans had been obtained. A smaller proportion of ID scans in the different cranial pathology groups (5 of 21 epilepsy cases, 4 of 9 vascular cases) resulted in further resections to meet the surgical goal of the surgeon. Two ID scans obtained during 5 procedures for the treatment of spinal disease did not lead to any change in surgery. Postoperative scans did not reveal any acute adverse events. There was 1 intraoperative adverse event in which a Greenberg retractor was inadvertently left on during ID scanning but was removed after the scout scans.

CONCLUSIONS

The application of iMR imaging in the pediatric neurosurgical population allows, at minimum, the opportunity to perform less invasive surgical exposures. Its potential is greatest when its high-quality imaging ability is coupled with its superior neuronavigation capabilities, which permits tracking of the extent of resection of intracranial tumors and, to a lesser extent, other lesions during the surgical procedure.

Selective amygdalohippocampectomy: the trans-middle temporal gyrus approach

The most common surgical procedure for the mesial temporal lobe is the standard anterior temporal resection or what is commonly called the anterior temporal lobectomy. There are, however, a number of other more selective procedures for removal of the mesial temporal lobe structures (amygdala, hippocampus, and parahippocampal gyrus) that spare much of the lateral temporal neocortex. Included in these procedures collectively referred to as selective amygdalohippocampectomy are the transsylvian, subtemporal, and transcortical (trans-middle temporal gyrus) selective amygdalohippocampectomy. In this manuscript the author reviews some of the surgical details of the trans-middle temporal gyrus approach to the mesial temporal structures.

Utility of neuronavigation and neuromonitoring in epilepsy surgery

The management of medically refractory epilepsy poses both a valuable therapeutic opportunity and a formidable technical challenge to epilepsy surgeons. Recent decades have produced significant advancements in the capabilities and availability of adjunctive tools in epilepsy surgery. In particular, image-based neuronavigation and electrophysiological neuromonitoring represent versatile and informative modalities that can assist a surgeon in performing safe and effective resections. In the present article the authors discuss these 2 subjects with reference to how they can be applied and what evidence supports their use. As technologies evolve with demonstrated and potential utility, it is important for all clinicians who deal with epilepsy to understand where neuronavigation and neuromonitoring stand in the present and what avenues for improvement exist for the future.

Tumor-biology and current treatment of skull-base chordomas

Chordomas are rare, slow growing tumors of the axial skeleton, which derive from the remnants of the fetal notochord. They can be encountered anywhere along the axial skeleton, most commonly in the sacral area, skull base and less commonly in the spine. Chordomas have a benign histopathology but exhibit malignant clinical behavior with invasive, destructive and metastatic potential. Genetic and molecular pathology studies on oncogenesis of chordomas are very limited and there is little known on mechanisms governing the disease. Chordomas most commonly present with headaches and diplopia and can be readily diagnosed by current neuroradiological methods. There are 3 pathological subtypes of chordomas: classic, chondroid and dedifferentiated chordomas. Differential diagnosis from chondrosarcomas by radiology or pathology may at times be difficult. Skull base chordomas are very challenging to treat. Clinically there are at least two subsets of chordoma patients with distinct behaviors: some with a benign course and another group with an aggressive and rapidly progressive disease. There is no standard treatment for chordomas. Surgical resection and high dose radiation treatment are the mainstays of current treatment. Nevertheless, a significant percentage of skull base chordomas recur despite treatment. The outcome is dictated primarily by the intrinsic biology of the tumor and treatment seems only to have a secondary impact. To date we only have a limited understanding this biology; however better understanding is likely to improve treatment outcome. Hereby we present a review of the current knowledge and experience on the tumor biology, diagnosis and treatment of chordomas.

Intraoperative MR imaging: preliminary results with 3 tesla MR system

Aim of this study is to present the initial clinical experience with 3 tesla intraoperative MR (ioMR).

MATERIAL AND METHODS

The 3T MRI suite is built adjacent to the neurosurgical operation theatre. The magnet room and the operation theatre are interconnected by a door and both RF-shielded. Before the operation, the magnet (3T Trio, Siemens) and the console rooms are disinfected. Whenever imaging is needed during the operation, the door is opened and the patient is transferred from the operation table to the magnet cradle. Axial, sagittal and/or coronal TSE T2, SE T1 and 3D Flash T1 weighted images (4-6 mm section thickness, 1 mm interslice gap) are obtained according to the lesion. Total examination time is approximately 10 minutes.

RESULTS

Twenty-six patients were examined with ioMR. There were ten female and seven male patients. Lesions were pituitary adenoma in 10, low grade glial tumor in 9, meningioma and high grade glial tumor in 2 each and metastasis, haemangioblastoma and chordoma in one each. Follow-up time was 1 to 9 months. In 16 patients the first intraoperative examination revealed gross total tumor excision. However, in 10 patients due to tumor remnants surgical intervention was continued and a second examination revealed gross total tumor excision in all. Postoperative routine MR examinations confirmed total tumor excision in all patients. No complication occurred in this series.

CONCLUSION

This small group of patients examined with ioMR demonstrated that the procedure is simple, helpful in achieving gross total tumor excision without complications.

Hirntumoren und Epilepsien

Improved tumor and epilepsy treatment requires long-term care of patients with symptomatic epilepsies caused by tumors. Pathophysiology, epidemiology, prognosis, drugs, and surgical treatment are discussed with special emphasis on seizure control, side effects, and quality of life. Because of the long-term course -- often 10 to 20 years -- optimal treatment strategies have to be selected individually. These should consider possibilities of new techniques of co-registering imaging and electrophysiology, surgery, and the interaction of anticonvulsive and chemotherapeutic drugs, cognition, and mood.

Comparing 0.2 tesla with 1.5 tesla intraoperative magnetic resonance imaging analysis of setup, workflow, and efficiency

RATIONALE AND OBJECTIVES

To compare low-field with high-field intraoperative magnetic resonance imaging (MRI) in respect to setup, workflow, and efficiency.

MATERIALS AND METHODS

A total of 750 patients were investigated either with a 0.2 T (March 1996-July 2001) or a 1.5 T (April 2002-August 2004) MRI system adapted for intraoperative use.

RESULTS

With the low-field setup, 330 patients were examined in 65 months; with the high-field setup, 420 patients were examined in 29 months, which is a 2.8-fold increase in cases per month (14.5 versus 5.1) reflecting improved ease of use. Concerning intraoperative workflow, the time for preparation to start intraoperative imaging decreased fivefold (2 minutes instead of 10 minutes); navigation was applied more often with 57% versus 51% (240/420 versus 167/330), whereas functional data were integrated in 35% versus 39% (84/240 versus 65/167). Application of navigation updates was doubled (22% versus 11%; 53/240 versus 18/167). Image acquisition time was reduced by a factor of two, allowing a more detailed imaging protocol, whereas the image quality is clearly improved in the high-field setup, where there was no difference between the standard preoperative image quality compared with the intraoperative quality. This contributed to an increased detection of tumor remnants and extended resections in pituitary (36% versus 29%; 47/129 versus 17/59) and glioma surgery (41% versus 26%; 38/93 versus 28/106).

CONCLUSION

Compared with the low-field setup, the high-field setup results not only in clearly superior image quality and increased imaging armamentarium, contributing to increased rates of detected tumor remnants, but also in a distinct improvement of intraoperative workflow. Furthermore, intraoperative high-field MRI offers various modalities beyond standard anatomic imaging, such as magnetic resonance spectroscopy, diffusion tensor imaging, and functional MRI.

1.5 T: intraoperative imaging beyond standard anatomic imaging

Intraoperative high-field MRI with integrated microscope-based neuronavigation is a safe and reliable technique providing immediate intraoperative quality control. Major indications are pituitary tumor, glioma, and epilepsy surgery. Intraoperative high-field MRI provides intraoperative anatomic images at high quality that are up to the standard of pre- and postoperative neuroradiologic imaging. Compared with previous low-field MRI systems used for intraoperative imaging, not only is the image quality is clearly superior but the imaging spectrum is much wider and the intraoperative work flow is improved. Furthermore, high-field MRI offers various modalities beyond standard anatomic imaging, such as magnetic resonance spectroscopy, diffusion tensor imaging, and functional MRI.

A low-field intraoperative MRI system for glioma surgery: is it worthwhile?

As intraoperative MRI expands its presence, its use will undoubtedly increase in glioma surgery. The foregoing discussion makes it clear that its benefits are unsurpassed by any other existing system. Because of their radiographic characteristics and gross appearance, gliomas are particularly suited for intraoperative MRI-guided surgery. It enables us to localize gliomas and define tumor margins precisely when, during surgery, the difference between tumor and brain is not easy to discern. The images generated during surgery serve as a detailed and updated map within which navigation is performed with utmost precision. Its significance is further highlighted when dealing with tumors in eloquent areas of the brain, where uncertainties over the location of tumor in relation to important brain structures can hinder the removal of tumor. By providing accurate positional information and in conjunction with cortical mapping techniques, intraoperative MRI enhances the confidence of the surgeon to go forward with resection or to stop when reaching important cortex. It allows us to perform the resection to the desired limit without causing injury to nearby important structures, thereby preventing postoperative neurologic deficits. The tracking system guides us in targeting each minute part of the tumor with unprecedented accuracy, and the ability to update images makes possible the constant evaluation of the progress of surgery. This near-real-time imaging can eliminate the errors brought about by the brain shifting that occurs throughout surgery. It also serves the important purpose of verifying the presence and position of any remaining tumor in the operative field. By means of sequential imaging, additional resection can be performed on any remaining tumor until imaging shows completion. The unwanted occurrence of finding residual tumor on a postoperative scan is thus practically eliminated. As a result, the surgical goal of complete or optimal resection can be achieved without any guesswork. Ultimately, what this means for the glioma patient is increased likelihood of longer survival brought about by a more thorough tumor resection. Intraoperative MRI addresses many of the surgical challenges posed by gliomas. As it becomes more available, there will come a point when the prevailing persuasion will be that some poorly defined tumors near eloquent cortex should not be operated on without intraoperative MRI. In the final analysis, not only is intraoperative MRI worthwhile but it will, in all likelihood, become a standard of care for many glioma cases.

Epilepsy surgery with intraoperative MRI at 1.5 T

Despite the infancy of iMRI in epilepsy surgery and the paucity of literature on this topic, some conclusions may be reached. Although iMRI is a useful adjunct during epilepsy procedures, a randomized control trial is necessary to determine its true impact.

Lesional mesial temporal lobe epilepsy and limited resections: prognostic factors and outcome

OBJECTIVES

To evaluate the influence of clinical, investigational, surgical, and histopathological factors on postoperative seizure relief in patients with mesial temporal lobe epilepsy (MTLE) due to lesions other than ammonshornsclerosis (AHS).

METHODS

Of 738 patients operated for TLE, 78 patients underwent limited resections for lesional MTLE (1990-2000). Seventy four patients with a follow up of more than one year were included. The preoperative clinical, neuropsychological, electroencephalogram, and neuroimaging characteristics were prospectively collected in a database. The histopathological material was re-examined.

RESULTS

The mean follow up was 49 months. Fifty eight patients were classified as seizure free (78.4% Class I), and six as almost seizure free (8.1% Class II), grouped together as satisfactory seizure control (64 patients, 86.5%). Five patients (6.8%) were categorised in Classes III and IV, respectively. These were grouped as unsatisfactory seizure control (10 patients, 13.5%). Surgical procedures were: 32 amygdalohippocampectomies (AH), 17 partial anterior AH, 15 AH plus polar resection, seven AH plus basal resection, and three AH plus extended temporal lesionectomy. There was no mortality and 2.7% mild permanent morbidity. Seizure relief did neither differ significantly with these approaches, nor with different classes of pathological findings (43 developmental tumours, 12 glial tumours, 10 dysplasias, and nine others). Even operation of dysplasias resulted in 80% satisfactory seizure control. Seizure onset during childhood proved to be a negative predictor for seizure relief (p = 0.020). MRI revealed 73 suspected lesions (98.6%), one dysembryoplastic neuroepithelial tumour was missed, in four cases no structural abnormalities could be confirmed with histopathological exam. Additionally, multifactorial regression revealed the factors "seizure onset after 10 years of age", "presence of complex partial seizures", "absence of a neurological deficit", and a "correlating neuropsychological deficit" as predictive for satisfactory seizure control.

CONCLUSIONS

"Preoperative tailoring" resulting in limit resections has proven to be safe and to provide a very good chance for satisfactory seizure relief in patients with lesional MTLE.

Intraoperative high-field-strength MR imaging: implementation and experience in 200 patients

PURPOSE

To review the initial clinical experience with intraoperative high-field-strength magnetic resonance (MR) imaging of brain lesions in 200 patients.

MATERIALS AND METHODS

Two hundred patients (mean age, 46.1 years; range, 7-84 years), most of whom had glioma or pituitary adenoma, were examined with a 1.5-T MR imager equipped with a rotating operating table and located in a radiofrequency-shielded operating theater. A navigation microscope placed inside the 0.5-mT zone and used in combination with a ceiling-mounted navigation system enabled integrated microscope-based neuronavigation. The extent of resection depicted at intraoperative imaging, the surgical consequences of intraoperative imaging, and the clinical practicability of the operating room setup were analyzed.

RESULTS

Seventy-seven resections with a transsphenoidal approach, 100 craniotomies, and 23 burr-hole procedures were performed. In 55 (27.5%) of 200 patients, intraoperative MR imaging had immediate surgical consequences (eg, extension of resection in 39% of patients with pituitary adenoma or glioma). In 108 patients the navigation system was used, and for 37 of those patients, functional imaging data were integrated into the navigation system. There was nearly no difference in quality between pre- and intraoperative images. Intraoperative workflow with intraoperative patient transport for imaging was straightforward, and imaging in most cases began less than 2 minutes after sterile covering of the surgical site. No complications resulted from high-field-strength MR imaging.

CONCLUSION

The high-field-strength MR imager was successfully adapted for intraoperative use with the integrated neuronavigation system. Intraoperative MR imaging provided valuable information that allowed intraoperative modification of the surgical strategy.

Current status of surgery in the management of epilepsy

PURPOSE

To review systematically the available evidence with regard to the current status of epilepsy surgery in the management of patients with epilepsy.

METHODS

A careful search of published literature, including Medline, published reviews, chapters, and cross-references thereof.

RESULTS

With medical treatment of epilepsy being unsuccessful in many cases, the importance of surgical approaches cannot be underscored. Early surgery is the treatment of choice for patients with clear-cut mesial temporal sclerosis and results in significant clinical improvement in up to 80% of cases, provided the EEG, neuropsychological, and neuropsychiatric results are in concordance with this approach. In patients with poorly defined, widespread, or dual pathology, however, invasive recordings may be necessary, and while this is performed in major centres, the outcome is rather more variable in this group. Improved surgical techniques, and the use of stereotactic approaches and image guidance procedures, have resulted in surgical resections becoming more selective. With isolated structural lesions such as dysembryoplastic tumours, low-grade astrocytomas, or focal vascular abnormalities, total macroscopic and radiological evidence of lesional excision is associated with excellent seizure-free outcome. The first randomised controlled trial of epilepsy surgery has demonstrated clearly the efficacy of these techniques, and the risk of complications.

DISCUSSION

Increasing sophistication of noninvasive presurgical evaluation enables surgical candidates to be identified at an earlier stage and presents a realistic alternative to medical treatment in many cases. The introduction of minimally invasive techniques has had a significant impact on surgical practice and its associated morbidity. The future of epilepsy surgery lies with continued basic science research and its application to clinical medicine.

Preoperative clinical evaluation, outline of surgical technique and outcome in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most common type of refractory epilepsy. The mechanisms of epileptogenesis and seizure semiology of the mesial and neocortical temporal lobe epilepsy are discussed. The evaluation and selection of patients for TLE surgery requires team work: the different clinical aspects of neuropsychological evaluation, magnetic resonance and functional imaging (positron emission tomography, single photon emission computed tomography and magnetoenephalography) are reviewed. In our programme of epilepsy surgery at Kuopio University Hospital, Finland, we have performed 230 temporal resections from 1988 until 2002. Preoperative diagnostic EEG-videotelemetry often required intracranial monitoring and it has proved to be safe and efficient. The indications and technique for tailored temporal lobe resection with amygdalohippocampectomy used in our institution, as well as the complications, are described. Our analysis of outcome after temporal lobe surgery included 140 consecutive adult patients between 1988 and 1999; one year after the operation in unilateral TLE the Engel I-II outcome was observed in 68% of the patients. Outcome of surgery improved significantly after introduction of the standardised MR imaging protocol from 1993; 74% of patients with unilateral TLE achieved Engel I-II outcome.

Functional neuronavigation and intraoperative MRI

Our concept of computer assisted surgery is based on the combination of intraoperative magnetic resonance (MR) imaging with microscope-based neuronavigation, providing anatomical and functional guidance simultaneously. Intraoperative imaging evaluates the extent of a resection, while the additional use of functional neuronavigation, which displays the position of eloquent brain areas in the operative field, prevents increasing neurological deficits, which would otherwise result from extended resections. Up to mid 2001 we performed intraoperative MR imaging using a low-field 0.2 Tesla scanner in 330 patients. The main indications were the evaluation of the extent of resection in gliomas, pituitary tumours, and in epilepsy surgery. Intraoperative MR imaging proved to serve as intraoperative quality control with the possibility of an immediate modification of the surgical strategy, i.e. extension of the resection. Integrated use of functional neuronavigation prevented increased neurological deficits. Compared to routine pre- or postoperative imaging being performed with high-Tesla machines, intraoperative image quality and sequence spectrum could not compete. This led to the development of the concept to adapt a high-field MR scanner to the operating environment, preserving the benefits of using standard microsurgical equipment and microscope-based neuronavigational guidance with integrated functional data, which was successfully implemented by April 2002. Up to the end of 2002, 95 patients were investigated with the new setup. Improved image quality, intraoperative workflow, as well as enhanced sophisticated intraoperative imaging possibilities are the major benefits of the high-field setup.

Beyond pharmacotherapy: surgical management

PURPOSE

To review the recent advances in the field of temporal lobe epilepsy (TLE) surgery.

RESULTS

TLE surgery has recently demonstrated a highly significant superiority over optimal medical therapy in a randomized trial. Accordingly, a median rate of 70% of class I outcome (patients free of disabling seizures postoperatively) has emerged from the pooling of all data published since the early 1990s. In addition, successful TLE surgery appears likely to reduce the risk of seizure-related death. However, it remains largely underused and overly delayed, partly because of the legitimate fears of possible surgical complications, such as verbal memory deficits or failure to control seizures. Reasons for surgical failures are not completely understood, and include bitemporal, pseudotemporal, and temporal-plus epilepsies, as well as insufficient resection of the mesial temporal structures. Developing techniques such as intraoperative MRI, gamma-knife radiosurgery, and various types of cranial nerves or intracerebral chronic stimulation have the potential to alleviate part of the limitations of TLE surgery.

CONCLUSIONS

The overall benefit of surgical treatment in patients with drug-resistant TLE should encourage a more frequent and earlier referral of such patients to epilepsy surgery centers. Important progress toward higher rates of seizure-free outcome and lower morbidity remains to be made and may be obtained by taking advantage of the new available technologies.

Anesthesia during high-field intraoperative magnetic resonance imaging experience with 80 consecutive cases

Intraoperative magnetic resonance imaging (MRI) has been used for years to update neuronavigation and for intraoperative resection control. For this purpose, low-field (0.1-0.2 T) MR scanners have been installed in the operating room, which, in contrast to machines using higher magnetic field strength, allowed the use of standard anesthetic and surgical equipment. However, these low-field MR systems provided only minor image quality and a limited battery of MR sequences, excluding functional MRI, diffusion-weighted MRI, or MR angiography and spectroscopy. Based on these advantages, a concept using high-field MRI (1.5 T) with intraoperative functional neuronavigational guidance has been developed that required adaptation of the anesthetic regimen to working in the close vicinity to the strong magnetic field. In this paper the authors present their experience with the first 80 consecutive patients who received anesthesia in a specially designed radio frequency-shielded operating room equipped with a high-field (1.5 T) MR scanner. We describe the MR-compatible anesthesia equipment used including ventilator, monitoring, and syringe pumps, which allow standard neuroanesthesia in this new and challenging environment. This equipment provides the use of total intravenous anesthesia with propofol and remifentanil allowing rapid extubation and neurologic examination following surgery. In addition, extended intraoperative monitoring including EEG monitoring required for intracranial surgery is possible. Moreover, problems and dangers related to the effects of the strong magnetic field are discussed.

Limited benefit of intraoperative low-field magnetic resonance imaging in craniopharyngioma surgery

OBJECTIVE

To investigate the benefit of intraoperative low-field magnetic resonance imaging (MRI) in craniopharyngioma surgery.

METHODS

We used a 0.2-T Magnetom Open scanner (Siemens Medical Solutions, Erlangen, Germany) that was located in a radiofrequency-shielded operating theater for intraoperative MRI. The head of the patient was placed in the fringe field of the scanner, so that standard microinstruments could be used. In transsphenoidal surgery, T1-weighted coronal and sagittal images were acquired. In transcranial surgery, a three-dimensional, gradient echo, T1-weighted, fast low-angle shot sequence was measured, thus allowing multiplanar reformatting.

RESULTS

A total of 21 surgical procedures in craniopharyngioma patients were investigated. In 10 patients, a bifrontal-translaminar approach was used; in 6 patients, the craniopharyngioma was removed via a transsphenoidal approach; and in 5 patients, intraoperative MRI was used to monitor cyst puncture and aspiration. In the craniotomy group, intraoperative imaging depicted a clear tumor remnant in one patient, which was subsequently removed. In another patient, an area of contrast enhancement was interpreted as artifact; however, postoperative follow-up at 3 months was suspicious for a minor remnant. Two of the eight patients with complete removal developed a recurrence during the follow-up period. In the group of patients who underwent primary transsphenoidal surgery (n = 4), complete removal was estimated by the surgeon in three cases. Intraoperative imaging depicted a remaining tumor in one case, leading to further tumor removal; however, follow-up revealed recurrent cysts.

CONCLUSION

Intraoperative low-field MRI allows an ultraearly evaluation of the extent of tumor removal in craniopharyngioma surgery in most cases. Imaging showing an incomplete resection offers the chance for further tumor removal during the same operation. However, intraoperative low-field MRI depicting a complete resection does not exclude craniopharyngioma recurrence.