Thalamic gliomas: Advances in the surgical management

Thalamic gliomas: Advances in the surgical management

Chapter 11 Thalamic gliomas: Advances in the surgical management Alice Hunga, Adela Wub, Christopher Jacksona and Michael Lima,c a Neurosurgery, Joh...

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Chapter 11

Thalamic gliomas: Advances in the surgical management Alice Hunga, Adela Wub, Christopher Jacksona and Michael Lima,c a

Neurosurgery, Johns Hopkins Hospital, Baltimore, MD, United States, bNeurosurgery, Stanford University, Palo Alto, CA, United States, cNeurosurgery, Oncology, and Institute of NanoBiotechnology, Johns Hopkins Hospital, Baltimore, MD, United States

Introduction Thalamic tumors are relatively uncommon, accounting for 1%–5% of all brain tumors.1–4 While lymphomas and metastases can present in this region, the majority of thalamic tumors are gliomas. These lesions are more common in the pediatric population, where the most common variant is juvenile pilocytic astrocytoma (JPA).5,6 Bilateral involvement is unusual and has a characteristic presentation, including personality changes and dementia.7–10 Given the deepseated location and proximity to critical structures, surgical access to thalamic gliomas is limited and early attempts at surgical resection were associated with high rates of morbidity and mortality.2,11 With recent advances, however, surgical resection has become a viable option for many of these lesions. Novel preoperative imaging techniques delineate eloquent structures; intraoperative ultrasound (US) and magnetic resonance imaging (MRI) can improve extent of resection; and the description of safe surgical corridors as well as minimally invasive retractor systems have improved access to this region. While many challenges still exist, treatment of thalamic gliomas has radically changed over the past decade. Surgical resection is now associated with significant improvements in survival and has become a part of standard management.

Preoperative evaluation Presentation Patients with thalamic tumors are frequently symptomatic at presentation. In the majority of cases, diagnosis is within a few months after symptom onset.3,12 Given the proximity of the ventricles, mass effect from the tumor can often lead to obstructive hydrocephalus. As a result, symptoms of elevated intracranial New Techniques for Management of ‘Inoperable’ Gliomas. © 2019 Elsevier Inc. All rights reserved.



New techniques for management of ‘inoperable’ gliomas

pressure (ICP), including headaches, nausea, and vomiting, are common upon initial presentation.3,13 Other common presenting symptoms are due to relationship of these lesions to eloquent structures. Contralateral hemiparesis from invasion of the internal capsule is the most common motor deficit, occurring in up to 40% of adult patients and 56%–75% of pediatric patients.3,11–19 Souweidane and Hoffman (1996) reported that thalamic gliomas occurring in the anterior and lateral regions often lead to motor symptoms, whereas medially and posteriorly situated tumors are more likely to result in hydrocephalus.20 This anatomic correlation has been corroborated in subsequent studies.3,11 Sensory deficits are less commonly seen, occurring in 27%–35% of adult patients and 0%–17% of children.3,12,14,15 Other presenting symptoms include visual changes, language dysfunction, movement disorders, seizures, and memory loss. Movement disorders, such as tremors and spasticity, may occur from the involvement of extrapyramidal areas.13 Hemorrhage into thalamic tumors results in rapid decline from acute hydrocephalus.13,15 Clinical presentation is a major consideration during surgical evaluation. In asymptomatic patients with an incidental diagnosis of a small thalamic glioma without radiographic evidence of aggressive features, it may be appropriate to delay surgery in favor of other management strategies. In these cases, the risk of surgery and damage to surrounding structures may outweigh the potential benefit. Conversely, for patients with acute symptoms from elevated ICP, emergent CSF (cerebrospinal fluid) diversion followed by surgical debulking is the treatment paradigm of choice. Even when gross total resection (GTR) is not possible, subtotal resection (STR) has also been shown to be beneficial. Cao et al. (2015) demonstrated that the median survival of those undergoing GTR or STR is 28 months, compared to 12 months for those who received partial resection or biopsy only.3 Furthermore, some patients were able to achieve improvement in their neurologic symptoms following surgery. For others, surgical resection reduced the rate symptom progression. Many of these effects are attributable to the relief of mass effect on surrounding structures. Unfortunately, a subset of patients either had no changes in their symptoms or experienced development of new deficits.3,15,21–23 Overall, these findings suggest that surgery is an effective treatment strategy in reducing morbidity and mortality of patients with thalamic gliomas, and presenting symptoms are crucial in guiding surgical evaluation (Table 1).

Conventional MRI The MRI is the most commonly used imaging modality in assessing thalamic tumors. Certain radiographic characteristics can be used to predict the tumor grading and its likely prognosis, thereby guiding the management strategy and surgical resection. Tumor volume, location, and involvement of neighboring structures are also essential for surgical planning.

TABLE 1 Survival outcomes and range of follow-up time for extent of resection and tumor grade.

7 (6.3%)

75 (67.6%)

29 (36.1%)

61 (54.9%)

50 (45.1%)

6–98 months

Median survival time: 12 months

Median survival time: 28–30 months

Median survival time: 28–30 months

94.7  3.6% (1 year SR)

43.2  7.5% (1 year SR)

57.7  8.1% (3 year SR)

6.8  3.8% (3 year SR)

16 (64%)

9 (36%)

Thalamic gliomas: Advances in the surgical management Chapter

4–132 months

–9 months


SR: 17 (94.4%)

SR: 1 (11.1%)

Range of follow-up time

Biopsy/no surgery

STR or partial resection


Low-grade glioma

High-grade glioma

n (%)

n (%)

n (%)

n (%)

n (%)

Steiger et al. (2000)21

– (0%)

4 (28.6%)

10 (71.4%)

4 (28.6%)

10 (71.4%) SR: 8 (80%)

6–52 months € Ozek and T€ ure (2002)23

– (0%)

2 (11.1%)

16 (88.9%)

3–24 months – (0%)

Moshel et al. (2007)22 1–20 years 3

Cinalli et al. (2017)15 –132 months SR, survival rate.

– (0%)

14 (19%)

58 (81%)

11–20 years

1–20 years

SR: 13 (92.3%)

SR: 57 (98.3%)

10 (40.0%)

15 (60.0%)

10 (76.9%)

3 (23.1%)

3–24 months

SR: 10 (100%)

SR: 0 (0%)

72 (100%)

– (0%)


Cao et al. (2015)



New techniques for management of ‘inoperable’ gliomas

Low-grade gliomas tend to have better defined borders, minimal or no contrast enhancement, and little surrounding edema on FLAIR (fluid-attenuated inversion recovery) imaging.24–26 High-grade gliomas are characteristically heterogeneously enhancing with areas of necrosis. Tumor margins are usually poorly delineated on T2 weighted imaging due to significant surrounding edema.5,25–27 The sensitivity and specificity of traditional MRI for distinguishing high- vs low-grade gliomas is 72.5% and 65.0%, respectively.28 Some highgrade gliomas can appear diffusely infiltrative with minimal contrast enhancement, while many low-grade gliomas may have aggressive-looking features.27 Therefore, obtaining tissue diagnosis, even when significant debulking is not possible, is critical to guiding adjuvant therapy. Conventional MRI sequences are unable to elucidate the location of eloquent structures that may be at risk during the surgical approach and/or tumor resection. Therefore, advanced imaging is frequently used for operative planning.

Diffusion tensor tractography The thalamus is subdivided into discrete nuclei, serving as relay stations for various sensory and motor signals. Each thalamic nucleus has a unique function and pattern of connectivity. Recent studies have explored the incorporation of thalamic segmentation, or radiographic identification of each thalamic nucleus, in preoperative planning to minimize injury. This technique utilizes diffusion tensor tractography (DTT), which is based on diffusion tensor imaging (DTI). The DTI is a type of MRI that measures the diffusion of water molecules to delineate neural tracts. Based on this data, tractography can then predict the anatomic connectivity and visualize distinct fiber bundles.29,30 Using this technique, thalamic segmentation can then be performed using different mathematical models.30,31 Thalamic segmentation has been studied for numerous clinical purposes. For example, Kim et al. (2016) explored the role of this technique in locating precise targets for deep brain stimulation in chronic pain patients.32 Others have applied this imaging technique to tumors located in other eloquent locations in determining the extent of resection and in planning the approach.33–35 Recently, Kis et al. (2014) evaluated the role of thalamic segmentation in preoperative surgical planning for thalamic gliomas. Five patients were included as a part of this study. In the first patient, DTI data was linked to T1 and FLAIR MRI sequences retrospectively, and the images were used to determine the cause of clinical decline after surgery. In subsequent patients, this technique was used preoperatively to plan the surgical approach. The authors were able to appreciate the relationship between the tumor and the thalamic nuclei, which allowed for the selection of safer surgical approaches. Variation from actual anatomy was within a few millimeters of error. Four out of the five patients received subtotal tumor resection (>80%), and three showed symptomatic improvement.36 While larger scale studies are needed,

Thalamic gliomas: Advances in the surgical management Chapter



these findings offer promising evidence for the application of thalamic segmentation in the treatment of thalamic gliomas. Berman et al. (2004) used DTI and intraoperative cortical stimulation to map the course of the pyramidal tract in glioma patients. The authors were able to clearly identify fiber bundles corresponding to specific movements; however, they noted that delineation became less accurate as the fiber tracts approached the tumor due to peritumoral edema. Nevertheless, implementation of this technique has the potential to reduce surgical morbidity.37 For patients with thalamic glioma, the portion of the corticospinal tract (CST) that runs along the posterior limb of the internal capsule (PLIC) is in the greatest danger of being injured. Tumors in this area can also cause displacement of the PLIC, disrupting the normal anatomic relationship. Unfortunately, the PLIC is difficult to identify using conventional MRI alone. This poses a challenge in determining the best surgical trajectory to avoid injury to the axonal fibers. In a small case series of six patients with thalamic JPA, Moshel et al. (2009) incorporated DTT as part of preoperative imaging. Using tractography, the authors were able to successfully visualize the PLIC and plan safe approaches. All patients had GTR of their lesions and experienced improvement in symptoms over time, suggesting that DTT can be useful in preventing iatrogenic complications.38 Other recently published studies have also reported successful results from using DTT as a part of preoperative planning for patients with thalamic gliomas (Table 2).39–41 The DTI is limited in its ability to resolve crossing fibers and area of termination, particularly in regions of disrupted anatomy associated with tumors and

TABLE 2 Percentage of patients receiving preoperative DTT planning.


No. of patients receiving DTT planning


No. of patients undergoing GTR

Moshel et al. (2009)38

6 (100%)

Pilocytic astrocytoma (100%)

6 (100%)

Broadway (2011)39

9 (90%)

Pilocytic astrocytoma (90%) Fibrillary astrocytoma (10%)

7 (70%)

Hou et al. (2012)41

59 (97%)

Weiner and Placantonakis (2017)40

1 (100%)

Pilocytic astrocytoma (100%)

1 (100%)


New techniques for management of ‘inoperable’ gliomas

peritumoral edema. To combat this phenomenon, high angular resolution diffusion imaging (HARDI) was developed.42,43 HARDI relies on multiple different diffusion-weighted (DW) image directions spaced throughout a spherical surface. Fernandez-Miranda et al. (2012) used this technique to create highdefinition fiber tracking (HDFT), which is able to reconstruct fiber tracts and crossings at a much higher resolution.44 A subsequent clinical study of three pediatric patients with low-grade thalamopeduncular glioma, two of whom underwent surgery, suggested that HDFT may be a valuable adjuvant for maximizing resection while minimizing injury to nearby fiber bundles. Importantly, the authors found that the tumor caused compression and displacement of the fiber tracts, rather than destruction.45 As a result, focus on decompression and preservation of these tracts is critical. There have been no published studies to date on the usage of HDFT in high-grade glioma.

Other magnetic resonance techniques In addition to conventional MRI and DTI, other MR sequences can be used to evaluate tumors characteristics. Perfusion weighted imaging (PWI) measures the vascular perfusion of tissues. In gliomas, PWI can potentially be used to predict WHO grading based on the apparent vascularity of the tumor with a sensitivity and specificity of 92% and 40%, respectively.46 Magnetic resonance spectroscopy (MRS) detects the concentration of various metabolites such as lactate and choline. Relative ratios of different substances can then be used to determine the type of tumor.47

Surgical management The goals of surgery are threefold: (1) procure tissue sample for histologic diagnosis, (2) reduce mass effect, and (3) cytoreduction. The role of stereotactic biopsy is debated. In asymptomatic patients, stereotactic biopsy may be useful for establishing a tissue diagnosis and guide further interventions. Symptomatic patients require surgical debulking for symptom relief, so upfront resection obviates the need for two separate procedures.16,20

Intraoperative neurophysiological monitoring Intraoperative neurophysiological monitoring (IONM) measures evoked potentials as a way to interrogate the integrity of the neural connections. Given the proximity of the PLIC and transcortical approaches near the motor cortex IONM is frequently used in the resection of these lesions. Carrabba et al. (2016) was the first group to publish a case series of thalamic glioma patients who had IONM. In addition to MEPs, direct electrical stimulation (DES) was used to locate the motor cortex. Electroencephalography (EEG) and electrocorticography (ECoG) were also performed in some patients. Two patients experienced transient weakness, but none had permanent motor deficits. The authors

Thalamic gliomas: Advances in the surgical management Chapter



suggested that IONM was crucial in the preservation of the PLIC.48 To better identify the PLIC intraoperatively, Akiyama et al. (2017) proposed using depth electrodes during surgery to monitor the motor fibers. This technique was used in 12 patients with thalamic tumors (7 gliomas), of which 4 achieved GTR and 6 had improved or no change to their Karnofsky performance score (KPS).49 Future work in this area will be required to determine optimal monitoring techniques and stimulation thresholds.

Intraoperative MRI Neuronavigation systems have become routine in surgical resection of intracranial tumors, particularly deep-seated lesions.50,51 One major limitation of this technology is brain shift, which occurs with tissue manipulation and CSF loss during surgery. This effect reduces the reliability of preoperative images in guiding surgical navigation. Intraoperative MRI can be used to compensate for these changes and improve the extent of resection.52,53 Intraoperative MRI is typically performed after gross removal of all visible tumor tissue, or when there is an increased risk of injuring critical structures nearby. The newly acquired images can then be used to evaluate the extent of resection and to update the navigational system if further resection is indicated.54,55 This practice has been widely adopted for intracranial tumor resection, and it has successfully reduced the need for repeat surgery and postoperative scans.56 In the setting of thalamic gliomas, Zheng et al. (2016) published a study of 38 patients who underwent intraoperative MRI. Conventional MRI and DTI images were obtained prior to surgery and linked to a neuronavigation system. After gross tumor resection was completed, an intraoperative MRI scanning was obtained. Surgery was terminated in 24 patients following initial imaging: 16 (42.1%) patients demonstrated GTR, while 8 (21.1%) had STR. The remaining 14 (36.8%) patients underwent further resection. Of these 14 patients, 10 received GTR following additional surgery. In three patients, hemorrhage was observed and was immediately evacuated; no patients experienced postoperative bleeding. The authors found that intraoperative imaging greatly improved the ability to achieve GTR and promoted early detection of hemorrhages.57

Intraoperative ultrasound US is another imaging modality that has been widely used intraoperatively to provide real-time feedback during resection of intracranial lesions. US can be used to help locate the tumor and to evaluate the extent of resection more quickly and cost effectively than intraoperative MRI. However, it is limited by the resolution and quality of images.58–60 One strategy to improve the interpretation of US images is to fuse them with MR images. By using intraoperative US images to update preoperative MR scans, the new information can be used to account for brain shift.61,62 Reinertsen et al. (2014) used vessels on preoperative


New techniques for management of ‘inoperable’ gliomas

MRA and intraoperative Doppler as landmarks for image registration, thereby allowing the two sets of scans to be integrated.63 Furthermore, Doppler US can also be used to detect major vessels and reduce the risk of vascular injury. This technique has been shown to be reliable in determining a safe trajectory for stereotactic brain tumor biopsy.64 Recently, superb microvascular imaging (SMI) was introduced as a novel US algorithm that can more precisely distinguish between flow signals and motion artifacts, permitting more detailed detection of microvasculature. The SMI feature is better at depicting tumor borders and intratumoral vasculature, distinguishing the tumor from surrounding healthy tissues.65 Another advancement in US technology that improves the resolution of tumor edges is contrast-enhanced US. Injection of contrast material causes tumor tissues to become hyperechoic and therefore more discernable from the normal brain. In addition, using contrast in combination with Doppler US further increases the Doppler signal in blood vessels, which is helpful in the setting of small intratumoral vessels, which can be difficult to appreciate otherwise.66–68 Several studies have examined the role of intraoperative US in the surgical resection of deep-seated tumors. While the device was reliable in localizing tumors, it was challenging in some cases to maintain a fluid filled cavity.69,70 In a large-scale study of 41 patients with thalamic glioma, Kiran et al. (2013) also found intraoperative US to be a fast and reliable way of both guiding the surgical approach and evaluating the extent of resection.71

Surgical approaches Surgical approaches are selected based on the location of the tumor within the thalamus, and relationship to neighboring structures. Preoperative computed tomography (CT) or MRI can provide valuable information about the focus and extension of the lesion. The thalamus is bounded ventrally by the hypothalamic sulcus, with the cerebral aqueduct at its caudal end and the foramen of Monroe at the rostral limit. The ventrolateral side of the thalamus abuts the subthalamic structures and internal capsule. Fibers of the thalamic radiations, which connect the thalamus to the cortex, emerge from the lateral aspects of the thalamus, forming the thalamic peduncles. The best candidate lesions for surgical resection are well circumscribed and noninfiltrating, although frequently the tumors will displace normal fibers of the CST. Cao et al. (2015) published a large series of 111 unilateral thalamic lesion resections and biopsies, employing transcallosal (27%), transfrontal (6%), transtemporal (6%), or transparieto-occipital transventricular (33%) approaches.3 Li et al. (2013) wrote a series on 27 patients with thalamic CM (cavernous malformation), using the following surgical approaches: posterior parieto-occipital transcortical (48.1%), parietal-occipital (14.8%), interhemispheric transcallosal (14.8%), subtemporal (11.1%), frontal-temporal (3.7%), and trans-superior frontal gyrus (3.7%).72 According to Rangel-Castilla and Spetzler (2015), 46 thalamic CM in

Thalamic gliomas: Advances in the surgical management Chapter



their series were categorized into 6 primary locations: anteroinferior, medial, lateral, posterosuperior, lateral posteroinferior, and medial posteroinferior, with recommended surgical trajectories for each locale.73 Moshel et al. (2007) also described three major locations for thalamic lesions and surgical approach recommendations: anterior, posterior, and posteroinferior thalamus.22 The transcortical-transventricular and intrahemispheric transcallosal approaches are the most frequent access routes for thalamic lesions. Frontal transventricular approaches are typically used for superolateral thalamic lesions, while occipital or parieto-occipital transventricular approaches are used for posterior thalamic tumors.4,21,74 Anterior thalamic lesions that displace the PLIC posteriorly can be accessed through the middle frontal gyrus75–77 As compared with the intrahemispheric transcallosal approach, transcortical approaches are less likely to be limited by veins draining into the superior sagittal sinus and spare potential injury to the anterior cerebral arteries. Drawbacks include greater risk to the internal capsule and the potential for postoperative seizures. The interhemispheric transcallosal approach is typically preferred for accessing lesions centered in the medial thalamus and avoids risking PLIC fibers, which are displaced laterally.38,72,73 The posterior interhemispheric transcallosal (PIT) approach affords access to medial lesions of the posterior thalamus.73,78 The posterosuperior transcortical trajectory can be used for lesions in the posterior thalamus and pulvinar that displace the PLIC anteriorly.38 The most common risk of posterior transcortical approaches is a persistent visual field. Cao et al. (2015) used the transparieto-occipital transventricular approach for thalamic lesions arising within the pulvinar with posterior extension, with careful sulcal dissection to decrease the risk of postoperative seizures and hemianopsia.3 The occipital transtentorial approach can also be used to access lesions involving the posterior thalamus that extend laterally.79 Lesions located in the lateral thalamus can be reached through the anterior contralateral transcallosal, transinsular, or transtemporal approaches.3 Thalamopeduncular tumors are located at the intersection of the inferior thalamus and cerebral peduncles. The surgeon can use a variety of surgical approaches, including transtemporal, subtemporal, and transparieto-occipital, depending on how much the thalamus itself is involved by the lesion. One series on 10 pediatric cases found anterolateral displacement of the CST to be most common, allowing for the use of a transcortical, middle temporal gyral approach.39 Transtemporal transchoroidal approaches through the middle temporal gyrus may be best utilized in circumstances where these thalamopeduncular lesions displace the anterolateral or medial aspects of the CST.80 Potential complications include hemianopia, oculomotor palsy, and tremor. Posteroinferior transcortical or subtemporal approaches may also be used to access these lesions.38 The subtemporal approach is particularly suited for tumors that project into the ambient cistern and extend inferiorly.3 Others promote the pterional transsylvian-transinsular approach for the resection of ventral posterior thalamic lesions, especially those with close proximity to the insula.23 In particular


New techniques for management of ‘inoperable’ gliomas

cases where either the tumor does not encroach to the ventricular space or if the CST fibers are distributed over the lateral aspect of the lesion, an alternative anterior interhemispheric transparaterminal gyrus approach should be used.81 The choice of approach should be tailored to each patient with particular attention paid to the location of the IC fibers, risk of injury to vascular structures, and potential for retraction injury to the fornices and cingulate gyrus. The risks and benefits of each approach must ultimately be evaluated in the context of the patient’s age, health status, and goals of surgery.

Minimal retraction systems Traditional methods of brain retraction during resection are not always well suited for access to deep-seated lesions, including thalamic tumors. Adverse sequelae from traditional retraction includes focal ischemia or postoperative cerebral edema secondary to prolonged pressure on brain parenchyma.82 There may also be undue damage to white matter fiber tracts. Minimal resection systems, such as tubular retractors and serial dilatation, provide a safe and effective way to facilitate various procedures from hematoma and intracerebral hemorrhage (ICH) evacuation to the removal of deep-seated intraaxial tumors and cysts. Currently, the most widely used systems are ViewSite Brain Access System (VBAS) (Vycor, Inc.) and BrainPath (NICO).83,84 The VBAS was used in nine adult and pediatric cases of various pathologies with successful resection or biopsy and minimal white matter injury.84 Another series of four pediatric patients, with ages ranging from 15 months to 16 years and pathologies including tumors located within the basal ganglia and pineal regions, demonstrated satisfactory resection or biopsy and no postoperative neurological deficits.85 Another case series of 20 tumors and colloid cysts removed through a minimally invasive retraction and resection system (VBAS or Brainpath) showed 90% rate of GTR with an overall long-term complication rate (5%) lower than the overall complication rate (9.1%) compiled from a meta-analysis of 536 cases previously described in the literature.86 In one retrospective investigation involving tubular brain retractors of three sizes (15, 18, and 23 mm), 14 out of 100 deep-seated intraaxial tumors arose from the basal ganglia or thalamus.87 Gross total and near-total resections were achieved in 78% of cases. Utilizing serial tubular dilatation and frameless navigation on 30 deep-seated intraventricular or intraparenchymal lesions, GTR was achieved for 70% of cases.88

Endoscopic resection of thalamic tumors and gliomas Endoscopes are commonly used to biopsy tumors and to perform endoscopic third ventriculostomies (ETV) for secondary obstructive hydrocephalus.89,90 Endoscope-assisted resection of deep-seated intracranial lesions has only been recently described but has the potential to gain traction as a safe and effective

Thalamic gliomas: Advances in the surgical management Chapter



option for glioma management in addition to biopsy and open craniotomy. Previously, one surgical series described four thalamic gliomas, located in the anterior aspect and protruding into either the lateral or third ventricle, biopsied with a standard rigid endoscope.91 In combination with the minimal retraction sheath, ViewSite, mounted rigid endoscopes were successfully used to resect or biopsy a variety of deep-seated tumors, including lymphomas and thalamic gliomas.92 Out of the series of 18 cases, GTR via a trans-cortical approach and endoscope was achieved for one right-sided thalamic metastatic tumor, 7 x 22 cm3 in size. Brokinkel et al. (2017) also described a case of left-sided thalamic glioma resected with a trans-sulcal approach through the left posterior horn of lateral ventricle, using neuroendoscopy.93

Laser therapy and resection Laser-interstitial thermal therapy (LITT) with neodymium: yttrium aluminum garnet (Nd:YAG) was first described in 1983 and has since then been used in thermal ablation procedures for a variety of pathologies, including epilepsy foci and intraparenchymal lesions.94 LITT under stereotactic or MRI guidance can provide precise concentrations of thermal energy for minimally invasive ablation in a controlled setting. Available LITT systems currently include Neuroblate (Monteris Medical, Michigan) and Visualase Thermal Therapy System (Visualase; Medtronic, Minnesota). In a trial on the first use of MR-LITT for ablation of metastatic brain tumors, six metastases were treated with no subsequent adverse effects and no recurrence within the ablation region.95 Schwarzmeier et al. (2005) described local application of LITT for debulking and cytoreduction of recurrent GBM in addition to the administration of adjuvant chemotherapy.96 Subsequent survival times for the two patients were 16 and 20 months, significantly longer than the mean survival of 34 weeks for patients undergoing solely systemic chemotherapy.96 Four patients with recurrent GBM underwent LITT following initial standard of care treatment.97 The mean and median overall survival following thermal ablation was 10.5 and 10 months, respectively, and overall survival for the cohort following primary diagnosis of GBM was 26 months. LITT may also be used as neoadjuvant therapy. In one study, 10 patients with unilateral tumors each larger than 10 cm3, underwent NeuroBlate LITT with subsequent resection through a trans-sulcal approach and use of minimally invasive retraction with VBAS assistance.98 Two patients out of the cohort had butterfly GBM, and one patient had a diagnosis of thalamic GBM. The median progression-free survival (PFS) for patients included in the series was roughly 9.3 months, compared to 4.6 months and 2.9 months PFS cited in other studies.99,100 In a meta-analysis of four articles with 25 included patients, median PFS following MR-LITT was 5.1 months with one instance of serious perioperative complication.101


New techniques for management of ‘inoperable’ gliomas

Guidance catheters Tumors in deep locations are difficult to reach due to a paucity of landmarks and a long distance to the target. Even with neuronavigation it may be difficult to continue along the correct trajectory due to brain shift. Furthermore, tumor borders may still be hard to discern after reaching the target. While intraoperative scanning could address some of these challenges, the need for multiple scans often increases operative time. Therefore, some surgeons have used guidance catheters as a way to aid localization. Using a stereotactic coordinate system based on preoperative images, target points around the tumor are established. Safe trajectories avoiding critical structures are determined, and entry points are marked. Subsequently, catheters are carefully inserted until they rest along the tumor’s margins. Dissection is done around the catheter until the tumor is reached. The biggest advantage of this technique is the ability to efficiently and quickly localize tumors, potentially decreasing the total operative time, and a more precise surgical corridor.102–104 Recently, Manjila et al. (2017) published a study on using intraoperative US to guide catheter placement for deep-seated brain tumors. Of 11 patients, 3 had thalamic gliomas. The authors used US to direct and confirm the placement of catheters around the tumor edges. Surgery then proceeded along the catheters until the tumor was reached and resected. The group found that this technique was fast and effective, with a high rate of GTR.105

Conclusion Thalamic gliomas are associated with poor prognosis and high morbidity and mortality. Because they have been difficult to access surgically, these tumors were historically considered “inoperable.” However, technological advances in imaging and surgical techniques have made surgical resection a more viable option. Preoperative DTI and HARDI render a more accurate representation of white matter tracts, and neuronavigation devices allow for more precise approaches. Intraoperative MRI and US have further increased surgical precision and safety. Moreover, minimally invasive retraction devices, endoscopic techniques, and LITT have also reduced the disruption of neighboring structures. These developments allow more proficient targeting of the tumor, minimizing iatrogenic injuries and associated complications, amplifying the role of surgery for the management of these challenging lesions.

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Thalamic gliomas: Advances in the surgical management Chapter



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