Category: Neuronavigation

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Does Navigated Transcranial Stimulation Increase the Accuracy of Tractography?

Does Navigated Transcranial Stimulation Increase the Accuracy of Tractography?

Neurosurgery 0:1–10, 2015

Tractography based on diffusion tensor imaging has become a popular tool for delineating white matter tracts for neurosurgical procedures.

OBJECTIVE: To explore whether navigated transcranial magnetic stimulation (nTMS) might increase the accuracy of fiber tracking.

METHODS: Tractography was performed according to both anatomic delineation of the motor cortex (n = 14) and nTMS results (n = 9). After implantation of the definitive electrode, stimulation via the electrode was performed, defining a stimulation threshold for eliciting motor evoked potentials recorded during deep brain stimulation surgery. Others have shown that of arm and leg muscles. This threshold was correlated with the shortest distance between the active electrode contact and both fiber tracks. Results were evaluated by correlation to motor evoked potential monitoring during deep brain stimulation, a surgical procedure causing hardly any brain shift.

RESULTS: Distances to fiber tracks clearly correlated with motor evoked potential thresholds. Tracks based on nTMS had a higher predictive value than tracks based on anatomic motor cortex definition (P < .001 and P = .005, respectively). However, target site, hemisphere, and active electrode contact did not influence this correlation.

CONCLUSION: The implementation of tractography based on nTMS increases the accuracy of fiber tracking. Moreover, this combination of methods has the potential to become a supplemental tool for guiding electrode implantation.

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Brain surface reformatted imaging (BSRI) for intraoperative neuronavigation in brain tumor surgery

Brain surface reformatted imaging (BSRI) for intraoperative neuronavigation in brain tumor surgery

Acta Neurochir (2015) 157:265–274

For safe resection of lesions situated in or near eloquent brain regions, determination of their spatial and functional relationship is crucial. Since functional magnetic resonance imaging and intraoperative neurophysiological mapping are not available in all neurosurgical departments, we aimed to evaluate brain surface reformatted imaging (BSRI) as an additional display mode for neuronavigation.

Methods Eight patients suffering from perirolandic tumors were preoperatively studied withMRI and navigated transcranial magnetic stimulation (nTMS). Afterwards, the MRI was automatically transformed into BSR images in neuronavigation software (Brainlab, Brainlab AG, Feldkirchen, Germany). One experienced neuroradiologist, one experienced neurosurgeon, and two residents determined hand representation areas ipsilateral to each tumor on two-dimensional (2D) MR images and on BSR images. All results were compared to results from intraoperative direct cortical mapping of the hand motor cortex and to preoperative nTMS results.

Results Findings from nTMS and intraoperative direct cortical mapping of the hand motor cortex were congruent in all cases. Hand representation areas were correctly determined on BSR images in 81.3%and on 2D-MR images in 93.75%(p= 0.26). In a subgroup analysis, experienced observers showed more familiarity with BSRI than residents (96.9 vs. 84.4 % correct results, p=0.19), with an equal error rate for 2D-MRI. The time required to define hand representation areas was significantly shorter using BSRI than using standard MRI (mean 27.4 vs. 40.4 s, p=0.04).

Conclusions With BSRI, a new method for neuronavigation is now available, allowing fast and easy intraoperative localization of distinct brain regions.

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Linear array ultrasound in low-grade glioma surgery: histology-based assessment of accuracy in comparison to conventional intraoperative ultrasound and intraoperative MRI

Linear array ultrasound in low-grade glioma surgery

Acta Neurochir (2015) 157:195–206

In low-grade glioma (LGG) surgery, intraoperative differentiation between tumor and most likely tumor-free brain tissue can be challenging. Intraoperative ultrasound can facilitate tumor resection. The aim of this study is to evaluate the accuracy of linear array ultrasound in comparison to conventional intraoperative ultrasound (cioUS) and intraoperative high-field MRI (iMRI).

Methods We prospectively enrolled 13 patients harboring a LGG of WHO Grade II. After assumed near total removal, a resection control was performed using navigated cioUS, navigated lioUS, and iMRI. We harvested 30 navigated biopsies from the resection cavity and compared the histopathological findings with the respective imaging results. Spearman’s rho was calculated to test for significant correlations. Sensitivity and specificity as well as receiver operating characteristics (ROC) were calculated to assess test performance of each imaging modality.

Results Imaging results of lioUS correlated significantly (p<0.009) with iMRI. Both iMRI and lioUS correlated significantly with final histopathological diagnosis (p<0.006, p<0.014). cioUS did not correlate with other imaging findings or with final diagnosis. The highest sensitivity for residual tumor detection was found in iMRI (83 %), followed by lioUS (79 %). The sensitivity of cioUS was only 21 %. Specificity was highest in cioUS (100 %), whereas iMRI and lioUS both achieved 67 %. ROC curves showed fair results for iMRI and lioUS and a poor result for cioUS.

Conclusions Intraoperative resection control in LGGs using lioUS reaches a degree of accuracy close to iMRI. Test results of lioUS are superior to cioUS. cioUS often fails to discriminate solid tumors from “normal” brain tissue during resection control. Only in lesions <10 cc cioUS does show good accuracy.

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Navigated Transcranial Magnetic Stimulation for “Somatotopic” Tractography of the Corticospinal Tract

SOMATOTOPIC RECONSTRUCTION OF CORTICOSPINAL TRACT

Operative Neurosurgery 10:542–554, 2014

Diffusion tensor imaging tractography provides 3-dimensional reconstruction of principal white matter tracts, but its spatial accuracy has been questioned. Navigated transcranial magnetic stimulation (nTMS) enables somatotopic mapping of the motor cortex.

OBJECTIVE: We used motor maps to reconstruct the corticospinal tract (CST) by integrating elements of its somatotopic organization. We analyzed the accuracy of this method compared with a standard technique and verified its reliability with intraoperative subcortical stimulation.

METHODS: We prospectively collected data from patients who underwent surgery between January 2012 and October 2013 for lesions involving the CST. nTMS-based diffusion tensor imaging tractography was compared with a standard technique. The reliability and accuracy between the 2 techniques were analyzed by comparing the number of fibers, the concordance in size, and the location of the cortical end of the CST and the motor area. The accuracy of the technique was assessed by using direct subcortical stimulation.

RESULTS: Twenty patients were enrolled in the study. nTMS-based tractography provided a detailed somatotopic reconstruction of the CST. This nTMS-based reconstruction resulted in a decreased number of fibers (305.16 231.7 vs 10246 193, P , .001) and a significantly greater overlap between the motor cortex and the cortical end-region of the CST compared with the standard technique (90.5 6 8.8% vs 58.3 6 16.6%, P , .001). Direct subcortical stimulation confirmed the CST location and the somatotopic reconstruction in all cases.

CONCLUSION: These results suggest that nTMS-based tractography of the CST is more accurate and less operator dependent than the standard technique and provides a reliable anatomic and functional characterization of the motor pathway.

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Inducing transient language disruptions by mapping of Broca’s area with modified patterned repetitive transcranial magnetic stimulation protocol

Mapping Broca’s area

J Neurosurg 120:1033–1041, 2014

Until now there has been no reliable stimulation protocol for inducing transient language disruptions while mapping Broca’s area. Despite the promising data of only a few studies in which speech arrest and language disturbances have been induced, certain concerns have been raised. The purpose of this study was to map Broca’s area by using event-related navigated transcranial magnetic stimulation (nTMS) to generate a modified patterned nTMS protocol.

Methods. Eleven right-handed subjects underwent nTMS to Broca’s area while engaged in a visual object-naming task. Navigated TMS was triggered 300 msec after picture presentation. The modified patterned nTMS protocol consists of 4 stimuli with an interstimulus interval of 6 msec; 8 or 16 of those bursts were repeated with a burst repetition rate of 12 Hz. Prior to mapping of Broca’s area, the primary motor cortices (M1) for hand and laryngeal muscles were mapped. The Euclidian distance on MRI was measured between cortical points eliciting transient language disruptions and M1 for the laryngeal muscle.

Results. On stimulating Broca’s area, transient language disruptions were induced in all subjects. The mean Euclidian distance between cortical spots inducing transient language disruptions and M1 for the laryngeal muscle was 17.23 ± 4.73 mm.

Conclusions. The stimulation paradigm with the modified patterned nTMS protocol was shown to be promising and might gain more widespread use in speech localization in clinical and research applications.

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The use of intraoperative navigation for complex upper cervical spine surgery

The use of intraoperative navigation for complex upper cervical spine surgery

Neurosurg Focus 36 (3):E5, 2014

Imaging guidance using intraoperative CT (O-arm surgical imaging system) combined with a navigation system has been shown to increase accuracy in the placement of spinal instrumentation. The authors describe 4 complex upper cervical spine cases in which the O-arm combined with the StealthStation surgical navigation system was used to accurately place occipital screws, C-1 screws anteriorly and posteriorly, C-2 lateral mass screws, and pedicle screws in C-6. This combination was also used to navigate through complex bony anatomy altered by tumor growth and bony overgrowth.

The 4 cases presented are: 1) a developmental deformity case in which the C-1 lateral mass was in the center of the cervical canal causing cord compression; 2) a case of odontoid compression of the spinal cord requiring an odontoidectomy in a patient with cerebral palsy; 3) a case of an en bloc resection of a C2–3 chordoma with instrumentation from the occiput to C-6 and placement of C-1 lateral mass screws anteriorly and posteriorly; and 4) a case of repeat surgery for a non-union at C1–2 with distortion of the anatomy and overgrowth of the bony structure at C-2.

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Navigation and imaging for endoscopic transnasal odontoid surgery

Experience with intraoperative navigation and imaging during endoscopic transnasal spinal approaches to the foramen magnum and odontoid

Neurosurg Focus 36 (3):E4, 2014

In this study the authors share their experience using intraoperative spinal navigation and imaging for endoscopic transnasal approaches to the odontoid in 5 patients undergoing C1–2 surgery for basilar invagination at Stanford Hospital and Clinics from 2010 to 2013.

Methods. Of these 5 patients undergoing C1–2 surgery for basilar invagination, 4 underwent a 2-tiered anterior C1–2 resection with posterior occipitocervical fusion during a first stage surgery, followed by endoscopic endonasal odontoidectomy in a separate setting. Intraoperative stereotactic navigation was performed using a surgical navigation system in all cases. Navigation accuracy, characterized as target registration error, ranged between 0.8 mm and 2 mm, with an average of 1.2 mm. Intraoperative imaging using a CT scanner was also performed in 2 patients.

Results. Endoscopic decompression of the brainstem was achieved in all patients, and no intraoperative complications were encountered. All patients were extubated within 24 hours after surgery and were able to swallow within 48 hours. After appropriate initial reconstruction of the defect at the craniocervical junction, no postoperative CSF leakage, arterial injury, or need for reoperation was encountered; 1 patient developed mild postoperative velopharyngeal insufficiency that resolved by the 6-month follow-up evaluation. There were no deaths and no patients required tracheostomy placement. The average inpatient stay after surgery varied between 72 and 96 hours, without extended intensive care unit stays for any patient.

Conclusions. Technologies such as intraoperative CT scanning and merged MRI/CT can provide the surgeon with detailed, virtual real-time information about the extent of complex endoscopic vertebral segment resection and brainstem decompression and lessens the prospect of revision or secondary procedures in this challenging surgical corridor. Moreover, patients experience limited morbidity and can tolerate early oral intake after transnasal endoscopic odontoidectomy. Essential to the successful undertaking of these endoscopic adventures is 1) an understanding of the endoscopic nasal, skull base, and neurovascular anatomy; 2) advanced and extended-length instrumentation including navigation; and 3) a team approach between experienced rhinologists and spine surgeons comfortable with endoscopic skull base techniques.

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Microsurgical resection of extensive craniopharyngiomas using a frontolateral approach

Microsurgical resection of extensive craniopharyngiomas using a frontolateral approach

J Neurosurg 120:559–570, 2014

An extensive craniopharyngioma is a tumor that extends into multiple compartments (subarachnoid spaces) and attains a size larger than 4 cm. A wide spectrum of approaches and strategies has been used for resection of such craniopharyngiomas. In this report the authors focused on the feasibility and efficacy of microsurgical resection of extensive craniopharyngiomas using a frontolateral approach.

Methods. A retrospective analysis was performed on 16 patients with extensive craniopharyngiomas who underwent operations using a frontolateral approach at one institution. The preoperative and postoperative clinical and radiological data, as well as the operative videos, were reviewed. The main focus of the review was the extent of radical tumor removal, early postoperative outcome, and approach-related complications.

Results. Gross-total resection of craniopharyngioma was achieved in 14 (87.5%) of 16 cases. Early after surgery (within 3 months), 1 patient showed improvement in hormonal status, while in the remaining 15 patients it worsened. No major neurological morbidity was observed. Two patients experienced temporary psychotic disorders. Visual function improved in 6 patients and remained unchanged in 9. One patient experienced a new bitemporal hemianopsia. Three patients with features of short-term memory disturbances at presentation did show improvement after surgery. There were no deaths or significant approach-related morbidity in this patient series. Only 1 patient required revision surgery for a CSF leak.

Conclusions. The safe and simple frontolateral approach provides adequate access even to extensive craniopharyngiomas and enables their complete removal with a reasonable morbidity and approach-related complication rate.

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Real-Time Atlas-Based Stereotactic Neuronavigation

Real-Time Atlas-Based Stereotactic Neuronavigation

Neurosurgery 74:128–134, 2014

Surgery for tumors in eloquent brain faces immense challenges when attempting to maximize resection and avoid neurological deficits.

OBJECTIVE: In order to give the surgeon real-time atlas-based anatomic information linked to the patient’s anatomy, we developed a software-based interface between deformable anatomic templates (DATs) and an intraoperative navigation system.

METHODS: Magnetic resonance imaging (MRI), diffusion tensor imaging, and/or functional MRI were performed on 3 patients preoperatively for the purposes of tumor resection by the use of neuronavigation. The DAT was registered to the patients’ navigation coordinate system and utilized coordinates from the navigation system during surgery. This provided the surgeon with a list of proximal anatomic and functional structures and a real-time image of the atlas at that location fused to the patient’s MRI. The clinical feasibility of this approach was evaluated during the resection of 3 eloquent tumors (right postcentral gyrus, left inferior frontal gyrus, and left occipital cuneus gyrus).

RESULTS: Tumor resection was performed successfully in all 3 patients. With the use of the coordinates from the navigation system, anatomic and functional structures and their distances were visualized interactively during tumor resection by using the DAT.

CONCLUSION: This is a proof of concept that an interactive atlas-based navigation can provide detailed anatomic and functional information that supplements MRI, diffusion tensor imaging, and functional MRI. The atlas-based navigation generated distances to important anatomic structures from the navigation probe tip. It can be used to guide direct electrical stimulation and highlight areas to avoid during tumor resection.

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The preoperative use of navigated transcranial magnetic stimulation facilitates early resection of suspected low-grade gliomas in the motor cortex

The preoperative use of navigated transcranial magnetic stimulation facilitates early resection of suspected low-grade gliomas in the motor cortex

Acta Neurochir (2013) 155:1813–1821

Resection is recommended for low-grade gliomas, but often it is not performed if the tumor is suspected of invading the primary motor cortex. The study aim is to assess what influence preoperative navigated transcranial magnetic stimulation (nTMS) has on the treatment strategy and clinical outcome for suspected low-grade gliomas in presumed motor eloquent location.

Methods This paper reports on all our patients with gliomas in the primary motor cortex that were non-enhancing on MRI, since we began using nTMS (n=11). For the comparison group, we identified the 11 most recent such patients just before we started using nTMS.

Results Exact delineation of motor functional versus nonfunctional cortical tissue was provided by nTMS in all cases, also within the area of altered FLAIR signal. In 6 out of 11 cases, the nTMS mapping result changed the treatment plan towards early and more extensive resection. Only one nTMS patient had another seizure within the follow-up period, whereas four patients in the comparison group had further seizures. In the nTMS group, 1 of 4 patients with pre-op neurological deficits improved by one year; whereas the comparison group had increased neurological deficits in 3 of the 8 patients not having surgery. The median (range) change of tumor volume from baseline to 1 year was −83 % (−67 % to −100 %) in the nTMS group, but +12 % (+40 % to −56 %) in the comparison group (p<0.001).

Conclusions nTMS provides accurate motor mapping results also in infiltrative gliomas and enables more frequent and more extensive surgical resection of non-enhancing gliomas in or near the primary motor cortex. The substantial differences observed here in neurological and oncological outcomes suggest that further comparative research is warranted.

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Intraoperative optical imaging for functional mapping

Intraoperative optical imaging for functional mapping

J Neurosurg 119:853–863, 2013

Intraoperative optical imaging (IOI) is an experimental technique used for visualizing functional brain areas after surgical exposure of the cerebral cortex. This technique identifies areas of local changes in blood volume and oxygenation caused by stimulation of specific brain functions. The authors describe a new IOI method, including innovative data analysis, that can facilitate intraoperative functional imaging on a routine basis. To evaluate the reliability and validity of this approach, they used the new IOI method to demonstrate visualization of the median nerve area of the somatosensory cortex.

Methods. In 41 patients with tumor lesions adjacent to the postcentral gyrus, lesions were surgically removed by using IOI during stimulation of the contralateral median nerve. Optical properties of the cortical tissue were measured with a sensitive camera system connected to a surgical microscope. Imaging was performed by using 9 cycles of alternating prolonged stimulation and rest periods of 30 seconds. Intraoperative optical imaging was based on blood volume changes detected by using a filter at an isosbestic wavelength (delta = 568 nm). A spectral analysis algorithm was used to improve computation of the activity maps. Movement artifacts were compensated for by an elastic registration algorithm. For validation, intraoperative conduction of the phase reversal over the central sulcus and postoperative evaluation of the craniotomy site were used.

Results. The new method and analysis enabled significant differentiation (p < 0.005) between functional and nonfunctional tissue. The identification and visualization of functionally intact somatosensory cortex was highly reliable; sensitivity was 94.4% and specificity was almost 100%. The surgeon was provided with a 2D high-resolution activity map within 12 minutes. No method-related side effects occurred in any of the 41 patients.

Conclusions. The authors’ new approach makes IOI a contact-free and label-free optical technique that can be used safely in a routine clinical setup. Intraoperative optical imaging can be used as an alternative to other methods for the identification of sensory cortex areas and offers the added benefit of a high-resolution map of functional activity. It has great potential for visualizing and monitoring additional specific functional brain areas such as the visual, motor, and speech cortex. A prospective national multicenter clinical trial is currently being planned.

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The Mirroring Technique: A Navigation-Based Method for Reconstructing a Symmetrical Orbit and Cranial Vault

Mirroring technique

Neurosurgery 73[ONS Suppl 1]:ons24–ons29, 2013

The reconstruction of orbital structures and the cranial vault curvature can be challenging after trauma or wide resections for tumors. Sophisticated methods have been developed recently, but these are resource- and time-consuming.

OBJECTIVE: We report the mirroring technique, which is an effective and costless application for navigation-guided reconstruction procedures.

METHODS: At the time of the reconstruction, high-resolution images are reloaded while forcing a left-right axial flip. The pointer subsequently enables a virtual 3- dimensional projection of the position of the contralateral normal anatomy.

RESULTS: This method was applied successfully in 2 cases of en plaque sphenoid wing meningiomas with secondary exophthalmia.

CONCLUSION: The mirroring technique represents an accurate method of outlining the contralateral normal anatomy onto the pathological side based on navigation guidance.

KEY WORDS:

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The reliability of topographic measurements from navigated transcranial magnetic stimulation in healthy volunteers and tumor patients

nTCM stimulationreliability

Acta Neurochir (2013) 155:1309–1317

Navigated transcranial magnetic stimulation (nTMS) is increasingly being used for preoperative mapping of the motor cortex. Any new technology should undergo rigorous validation before being widely adopted in routine clinical practice.

The aim of this experimental study was to assess the intraexaminer and interexaminer reliability of topographic mapping with nTMS.

Methods nTMS mapping of the motor cortex for the first dorsal interosseous (FDI) muscle was performed by an expert and a novice examiner, twice in ten healthy volunteers and once in ten tumor patients. The distances between the centers-of-gravity and hotspots were calculated, as were coefficients of variation. This study also compared orthogonal versus variable orientation of the stimulation coil.

Results The mean (range) distance between centers-of-gravity for the expert examiner in the test–retest protocol with healthy volunteers was 4.40 (1.86–7.68)mm. The mean (range) distance between centers-of-gravity for the expert vs. novice examiner was 4.89 (2.39–9.22) mm. There were no significant differences in this result between healthy volunteers and tumor patients.

Conclusions nTMS is sufficiently reliable for clinical use, but examiners should make efforts to minimize sources of error. The reliability of nTMS in tumor patients appears comparable to healthy subjects.

Keywords

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The Silent Loss of Neuronavigation Accuracy

The_Silent_Loss_of_Neuronavigation_Accuracy___A-1

Neurosurgery 72:796–807, 2013

Neuronavigation has become an intrinsic part of preoperative surgical planning and surgical procedures. However, many surgeons have the impression that accuracy decreases during surgery.

OBJECTIVE: To quantify the decrease of neuronavigation accuracy and identify possible origins, we performed a retrospective quality-control study.

METHODS: Between April and July 2011, a neuronavigation system was used in conjunction with a specially prepared head holder in 55 consecutive patients. Two different neuronavigation systems were investigated separately. Coregistration was performed with laser-surface matching, paired-point matching using skin fiducials, anatomic landmarks, or bone screws. The initial target registration error (TRE1) was measured using the nasion as the anatomic landmark. Then, after draping and during surgery, the accuracy was checked at predefined procedural landmark steps (Mayfield measurement point and bone measurement point), and deviations were recorded.

RESULTS: After initial coregistration, the mean (SD) TRE1 was 2.9 (3.3) mm. The TRE1 was significantly dependent on patient positioning, lesion localization, type of neuroimaging, and coregistration method. The following procedures decreased neuronavigation accuracy: attachment of surgical drapes (DTRE2 = 2.7 [1.7] mm), skin retractor attachment (DTRE3 = 1.2 [1.0] mm), craniotomy (DTRE3 = 1.0 [1.4] mm), and Halo ring installation (DTRE3 = 0.5 [0.5] mm). Surgery duration was a significant factor also; the overall DTRE was 1.3 [1.5] mm after 30 minutes and increased to 4.4 [1.8] mm after 5.5 hours of surgery.

CONCLUSION: After registration, there is an ongoing loss of neuronavigation accuracy. The major factors were draping, attachment of skin retractors, and duration of surgery. Surgeons should be aware of this silent loss of accuracy when using neuronavigation.

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Merging machines with microsurgery: clinical experience with neuroArm

Merging machines with microsurgery- clinical experience with neuroArm

J Neurosurg 118:521–529, 2013

It has been over a decade since the introduction of the da Vinci Surgical System into surgery. Since then, technology has been advancing at an exponential rate, and newer surgical robots are becoming increasingly sophisticated, which could greatly impact the performance of surgery. NeuroArm is one such robotic system.

Methods. Clinical integration of neuroArm, an MR-compatible image-guided robot, into surgical procedure has been developed over a prospective series of 35 cases with varying pathology.

Results. Only 1 adverse event was encountered in the first 35 neuroArm cases, with no patient injury. The adverse event was uncontrolled motion of the left neuroArm manipulator, which was corrected through a rigorous safety review procedure. Surgeons used a graded approach to introducing neuroArm into surgery, with routine dissection of the tumor-brain interface occurring over the last 15 cases. The use of neuroArm for routine dissection shows that robotic technology can be successfully integrated into microsurgery. Karnofsky performance status scores were significantly improved postoperatively and at 12-week follow-up.

Conclusions. Surgical robots have the potential to improve surgical precision and accuracy through motion scaling and tremor filters, although human surgeons currently possess superior speed and dexterity. Additionally, neuroArm’s workstation has positive implications for technology management and surgical education. NeuroArm is a step toward a future in which a variety of machines are merged with medicine.

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Intraoperative visualisation of language fascicles by diffusion tensor imaging-based tractography in glioma surgery

Intraop visualization language fascicles-3

Acta Neurochir (2013) 155:437–448

For gliomas, the goal of surgery is to maximise the extent of resection (EOR) while minimising the postoperative morbidity. The purpose of this study was to evaluate the benefits of a protocol developed for the surgical management of gliomas located in language areas, where tractography-integrated navigation was used in conjunction with direct electrical stimulations (DES).

Methods and materials The authors included ten patients suffering of gliomas located in language areas. The preoperative planning for multimodal navigation was done by integrating anatomical magnetic resonance images and subcortical pathway volumes generated by diffusion tensor imaging. Six white matter fascicles implicated in language functions were reconstructed in each patient, including fibres for phonological processing (i.e. the arcuate fasciculus), fibres for lexical-semantic processing (i.e. the inferior frontooccipital fasciculus, inferior longitudinal fasciculus and uncinate fasciculus), and two premotor fasciculi involved in the preparation of speech movements (the subcallosal medialis fasciculus and cortical fibres originating from the medial and lateral premotor areas). During surgery, language fascicles were identified by direct visualisation on tractography-integrated navigation images and by observing transient language inhibition after subcortical DES. Language deficits were evaluated preoperatively and postoperatively, and compared with the EOR.

Results Tractography was successfully performed in all patients, preoperatively demonstrating the relationships between the tumours to resect and the language fascicles to preserve from injury. With the use of the tractographyintegrated navigation system and intraoperative DES, language functions were preserved in all patients. The mean volumetric resection was 93.0±10.4 % of the preoperative tumour volume, with a gross total resection in 60 % of patients.

Conclusion The intraoperative combination of tractography and DES contributed to maximum safe resection of gliomas located in language areas.

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Placement of thoracolumbar pedicle screws using O-arm-based navigation

Placement of thoracolumbar pedicle screws using O-arm-based navigation- technical note on controlling the operational accuracy of the navigation system

Neurosurg Rev (2013) 36:157–162

Suboptimal placements of pedicle screws may lead to neurological and vascular complications. Computer-assisted image guidance has been shown to improve accuracy in spinal instrumentation.Checking the accuracy of the navigation system during pedicle screw placement is fundamental.

We describe a novel technique of using continuous accuracy check of the navigation system during O-arm based neuronavigation to instrument the thoracolumbar region.

Forty thoracic and 42 lumbar screws were inserted in 12 patients. The Mirza evaluation system was used to evaluate the accuracy of the inserted screws. There was no neurological injury and no need to reposition any screw. The accuracy of the screws placement was excellent.

Our technique of continuous at will operational accuracy check of the neuronavigation system is associated with extreme accuracy of screw placement, no need to bring a patient back to the operating room to reposition a pedicle screw, and with excellent outcome.

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Transphenoidal surgery in acromegalic patients: anatomical considerations and potential pitfalls

Transphenoidal surgery in acromegalic patients- anatomical considerations and potential pitfalls.1 Transphenoidal surgery in acromegalic patients- anatomical considerations and potential pitfalls

Acta Neurochir (2013) 155:125–130

Transphenoidal surgery is an effective treatment for acromegalic patients with growth hormone (GH) producing pituitary adenomas. Since acromegaly is a systemic disease which causes multiple bony alterations, we hypothesized that it could affect the sphenoid sinus anatomy. The aim of the study was to determine whether acromegalic patients have sphenoid sinus alterations with potential surgical impact.

Methods Fourty-six consecutive patients (23 acromegalics- GH group, 23 non-acromegalics-nGH group) undergoing transphenoidal surgery were included in this study. Preoperative volumetric CT scan of the head was used to assess the following anatomic characteristics: type of sphenoid sinus (sellar, pre-sellar, conchal); number of intrasphenoid septa; number of carotid-directed septa; intercarotid distance; depth of the sphenoid sinus; depth and size of the sella.

Results The sphenoid sinus was of the pre-sellar/conchal type in 26 % of the patients with acromegaly (n023) versus 9 % of the patients of the nGH group (n023). The number of intrasphenoid septations was significantly higher in the GH group than in the nGH group (P=.03). Interestingly, the intercarotid distance was smaller in GH patients than in nGH displaying a trend toward significance (P=.05). The sphenoid bone was deeper in the GH group as compared to the nGH group (P=.01) but the distance sphenoid sinus-sella was reduced (P<.01). Finally, the sella was not deeper, nor larger in acromegalic patients.

Conclusions The sphenoid sinus of acromegalic patients resulted in being deeper, characterized by more septa and by a reduced intercarotid distance. These alterations deserve special pre- and intraoperative care, being potentially responsible for surgical difficulties.

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Clinical Application of Motor Pathway Mapping Using Diffusion Tensor Imaging Tractography and Intraoperative Direct Subcortical Stimulation in Cerebral Glioma Surgery

Neurosurgery 71:1170–1184, 2012

Glioma surgery in eloquent areas remains a challenge because of the risk of postoperative motor deficits.

OBJECTIVE: To prospectively evaluate the efficiency of using a combination of diffusion tensor imaging (DTI) tractography functional neuronavigation and direct subcortical stimulation (DsCS) to yield a maximally safe resection of cerebral glioma in eloquent areas.

METHODS: A prospective cohort study was conducted in 58 subjects with an initial diagnosis of primary cerebral glioma within or adjacent to the pyramidal tract (PT). The white matter beneath the resection cavity was stimulated along the PT, which was visualized with DTI tractography. The intercept between the PT border and DsCS site was measured. The sensitivity and specificity of DTI tractography for PT mapping were evaluated. The efficiency of the combined use of both techniques on motor function preservation was assessed.

RESULTS: Postoperative analysis showed gross total resection in 40 patients (69.0%). Seventeen patients (29.3%) experienced postoperative worsening; 1-month motor deficit was observed in 6 subjects (10.3%). DsCS verified a high concordance rate with DTI tractography for PT mapping. The sensitivity and specificity of DTI were 92.6% and 93.2%, respectively. The intercepts between positive DsCS sites and imaged PTs were 2.0 to 14.7 mm (5.262.2 mm). The 6-month Karnofsky Performance Scale scores in 50 postoperative subjects were significantly increased compared with their preoperative scores.

CONCLUSION: DTI tractography is effective but not completely reliable in delineating the descending motor pathways. Integration of DTI and DsCS favors patient-specific surgery for cerebral glioma in eloquent areas.

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Management of C2 fractures using Iso-C3D guidance

Acta Neurochir 154 (10):1781-1787, 2012

About 20 % of cervical fractures involve the C2 vertebra. Many surgical techniques have been proposed according to the type of fracture. However, morbidity and mortality of these procedures is often high, which can be attributed to the old age and significant co-morbidities of the affected population and the complex anatomy of C2. To target the latter, several authors have applied iso-C3D guidance for most of the common techniques. We here present our experience using a fixed protocol and iso-C3D guidance in all cases of traumatic C2 fractures.
Methods: Sixteen patients were operated upon between April 2011 and April 2012 using Iso-C3D guidance, following a fixed routine protocol. The screw position was verified by CT-scanning. Intraoperative and clinical parameters were evaluated.
Results: Six patients received anterior lag-screw fixation of odontoid fractures. Two underwent isolated posterior lag-screw fixation of hangman’s fracture. C1 and/or C3 lateral mass, and/or C2 isthmic screws were placed in eight patients. No screw had to be revised, 3 minor breachings of the cortical bone of <2 mm were observed.The same standard protocol for draping, registration of the navigation and Iso-C3D guided drilling could be applied for anterior and posterior procedures, leaving only two variables. This led to rapid acceptance of the technique among OR-staff and surgeons, who felt comfortable with iso-C3D guidance after only five cases.
Conclusions: Iso-C3D guidance is a safe and straightforward technique for anterior and posterior screw placement in the upper cervical spine.

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