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Neuronavigation applied to epilepsy monitoring with subdural electrodes

Technical Note

Roukoz B. Chamoun, Vikram V. Nayar, and Daniel Yoshor

Accurate localization of the epileptogenic zone is of paramount importance in epilepsy surgery. Despite the availability of noninvasive structural and functional neuroimaging techniques, invasive monitoring with subdural electrodes is still often indicated in the management of intractable epilepsy. Neuronavigation is widely used to enhance the accuracy of subdural grid placement. It allows accurate implantation of the subdural electrodes based on hypotheses formed as a result of the presurgical workup, and can serve as a helpful tool for resection of the epileptic focus at the time of grid explantation. The authors describe 2 additional simple and practical techniques that extend the usefulness of neuronavigation in patients with epilepsy undergoing monitoring with subdural electrodes. One technique involves using the neuronavigation workstation to merge preimplantation MR images with a postimplantation CT scan to create useful images for accurate localization of electrode locations after implantation. A second technique involves 4 holes drilled at the margins of the craniotomy at the time of grid implantation; these are used as fiducial markers to realign the navigation system to the original registration and allow navigation with the merged image sets at the time of reoperation for grid removal and resection of the epileptic focus. These techniques use widely available commercial navigation systems and do not require additional devices, software, or computer skills. The pitfalls and advantages of these techniques compared to alternatives are discussed.

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Neuroendoscopic fenestration of glioependymal cysts to the ventricle: report of 3 cases

Anthony M. Alvarado, Kyle A. Smith, and Roukoz B. Chamoun

Glioependymal cysts are rare congenital lesions of the central nervous system. Reported surgical treatments of these lesions have varied and yielded mixed results, and the optimal surgical strategy is still controversial. The authors here report the clinical and surgical outcomes for three adult patients successfully treated with neuroendoscopic fenestration into the ventricular system. The patients had presented with symptomatic glioependymal cysts in the period from 2013 to 2016 at the authors’ institution. All underwent minimally invasive neuroendoscopic fenestration of the glioependymal cyst into the lateral ventricle via a stereotactically guided burr hole. Presenting clinical and radiological findings, operative courses, and postintervention outcomes were evaluated.

All three patients initially presented with symptoms related to regional mass effect of the underlying glioependymal cyst, including headaches, visual disturbances, and hemiparesis. All patients were successfully treated with endoscopic fenestration of the cyst wall into the lateral ventricle, where the wall was thinnest. Postoperatively, all patients reported improvement in their presenting symptoms, and neuroimaging demonstrated decompression of the cyst. Clinical follow-up ranged from 4 months to 5 years without evidence of reexpansion of the cyst or shunt requirement.

Compared to open resection and shunting of the cyst contents, minimally invasive endoscopic fenestration of a glioependymal cyst into the ventricular system is a safe and effective surgical option. This approach is practical, is less invasive than open resection, and appears to provide a long-term solution.

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Outcome in patients with blunt head trauma and a Glasgow Coma Scale score of 3 at presentation

Clinical article

Roukoz B. Chamoun, Claudia S. Robertson, and Shankar P. Gopinath

Object

A Glasgow Coma Scale (GCS) score of 3 on presentation in patients with severe traumatic brain injury due to blunt trauma has been recognized as a bad prognostic factor. The reported mortality rate in these patients is very high, even approaching 100% in the presence of fixed and dilated pupils in some series. Consequently, there is often a tendency to treat these patients less aggressively because of the low expectations for a good recovery. In this paper, the authors' purpose is to report their experience in the management of this patient population, analyzing the mortality rate, prognostic factors, and functional outcome of survivors.

Methods

The authors performed a retrospective review of patients who presented between 1997 and 2007 with blunt head trauma and a GCS score of 3. Demographics, mechanism of injury, examination, blood alcohol level, associated injury, intracranial pressure (ICP), surgical procedures, and outcome were all recorded.

Results

A total of 189 patients met the inclusion criteria and were included in this study. The overall mortality rate was 49.2%. At the 6-month follow-up, 13.2% of the entire series achieved a good functional outcome (Glasgow Outcome Scale [GOS] score of 1 or 2).

The patient population was then divided into 2 groups: Group 1 (patients who survived [96]) and Group 2 (patients who died [93]). Patients in Group 1 were younger (mean 33.3 ± 12.8 vs 40.3 ± 16.97 years; p = 0.002) and had lower ICP on admission (mean 16.3 ± 11.1 vs 25.7 ± 12.7 mm Hg; p < 0.001) than those in Group 2. The difference between the 2 groups regarding sex, mechanism of injury, hypotension on admission, alcohol, surgery, and associated injuries was not statistically significant.

The presence of bilateral fixed, dilated pupils was found to be associated with the highest mortality rate (79.7%). Although not statistically significant because of the sample size, pupil status was also a good predictor of the functional outcome at the 6-month follow-up; a good functional outcome (GOS Score 1 or 2) was achieved in 25.5% of patients presenting with bilateral reactive pupils, and 27.6% of patients presenting with a unilateral fixed, dilated pupil, compared with 7.5% for those presenting with bilateral fixed, nondilated pupils, and 1.4% for patients with bilateral fixed, dilated pupils.

Conclusions

Overall, 50.8% of patients survived their injury and 13.2% achieved a good functional outcome after at 6 months of follow-up (GOS Score 1 or 2). Age, ICP on admission, and pupil status were found to be significant predictive factors of outcome. In particular, pupil size and reactivity appeared to be the most important prognostic factor since the mortality rate was 23.5% in the presence of bilateral reactive pupils and 79.7% in the case of bilateral fixed, dilated pupils. The authors believe that patients having suffered traumatic brain injury and present with a GCS score of 3 should still be treated aggressively initially since a good functional outcome can be obtained in some cases.

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Computed tomography morphometric analysis for axial and subaxial translaminar screw placement in the pediatric cervical spine

Clinical article

Joshua J. Chern, Roukoz B. Chamoun, William E. Whitehead, Daniel J. Curry, Thomas G. Luerssen, and Andrew Jea

Object

The management of upper cervical spinal instability in children continues to represent a technical challenge. Traditionally, a number of wiring techniques followed by halo orthosis have been applied; however, they have been associated with a high rate of nonunion and poor tolerance for the halo. Alternatively, C1–2 transarticular screws and C-2 pars/pedicle screws allow more rigid fixation, but their placement is technically demanding and associated with vertebral artery injuries. Recently, C-2 translaminar screws have been added to the armamentarium of the pediatric spine surgeon as a technically simple and biomechanically efficient means of fixation. However, the use of subaxial translaminar screws have not been described in the general pediatric population. There are no published data that describe the anatomical considerations and potential limitations of this technique in the pediatric population.

Methods

The cervical vertebrae of 69 pediatric patients were studied on CT scans. Laminar height and thickness were measured. Statistical analysis was performed using unpaired Student t-tests (p < 0.05) and linear regression analysis.

Results

The mean laminar heights at C-2, C-3, C-4, C-5, C-6, and C-7, respectively, were 9.76 ± 2.22 mm, 8.22 ± 2.24 mm, 8.09 ± 2.38 mm, 8.51 ± 2.34 mm, 9.30 ± 2.54 mm, and 11.65 ± 2.65 mm. Mean laminar thickness at C-2, C-3, C-4, C-5, C-6, and C-7, respectively, were 5.07 ± 1.07 mm, 2.67 ± 0.79 mm, 2.18 ± 0.73 mm, 2.04 ± 0.60 mm, 2.52 ± 0.66 mm, and 3.84 ± 0.96 mm. In 50.7% of C-2 laminae, the anatomy could accept at least 1 translaminar screw (laminar thickness ≥ 4 mm).

Conclusions

Overall, the anatomy in 30.4% of patients younger than 16 years old could accept bilateral C-2 translaminar screws. However, the anatomy of the subaxial cervical spine only rarely could accept translaminar screws. This study establishes anatomical guidelines to allow for accurate and safe screw selection and insertion. Preoperative planning with thin-cut CT and sagittal reconstruction is essential for safe screw placement using this technique.

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Extracranial traumatic carotid artery dissections in children: a review of current diagnosis and treatment options

Roukoz B. Chamoun, Michel E. Mawad, William E. Whitehead, Thomas G. Luerssen, and Andrew Jea

Object

Currently, no diagnostic or treatment standards exist for extracranial carotid artery dissection (CAD) in children after trauma. The purpose of this study was to review and describe the characteristics, diagnosis, and treatment of this rather uncommon sequelae of pediatric trauma.

Methods

A systematic review of the literature was performed to examine the pertinent studies of traumatic extracranial carotid artery (CA) injuries in children.

Results

No randomized trials were identified; however, 19 case reports or small case series consisting of 34 pediatric patients were found in the literature. The diagnosis of CAD was made in 33 of 34 patients only after the onset of ischemic symptomatology. Twenty-four of 34 patients underwent cerebral angiography to confirm diagnosis; MR angiography affirmed the diagnosis in 6 of 34 patients. There was little published experience with CA ultrasonography or CT angiography for diagnosis. Thirty of 34 patients were treated with medical therapy or observation; 2 of 4 patients treated with observation alone died. There was little experience with open surgical treatment of CAD in the pediatric population, and there were no studies on the endovascular treatment of traumatic CAD in children. The literature does not support anticoagulation therapy over antiplatelet therapy.

Conclusions

As a result of this review of the literature, the authors propose the algorithms for the evaluation and treatment of traumatic extracranial CADs in children. These recommendations include utilizing MR angiography as a screening tool in cases in which the clinical suspicion of CAD is high, using conventional cerebral angiography to confirm the diagnosis, implementing antiplatelet therapy as initial medical management, and reserving endovascular stenting in cases of failed medical treatment.

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Extracranial traumatic carotid artery dissections in children

Robert H. Rosenwasser

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Computed tomography morphometric analysis for C-1 lateral mass screw placement in children

Clinical article

Roukoz B. Chamoun, William E. Whitehead, Daniel J. Curry, Thomas G. Luerssen, and Andrew Jea

Object

The use of C-1 lateral mass screws provides an alternative to C1–2 transarticular screws in the pediatric population. However, the confined space of the local anatomy and unfamiliarity with the technique may make the placement of a C-1 lateral mass screw more challenging, especially in the juvenile or growing spine.

Methods

A CT morphometric analysis was performed in 76 pediatric atlases imaged at Texas Children's Hospital from October 1, 2007 until April 30, 2008. Critical measurements were determined for potential screw entry points, trajectories, and lengths, with the goal of replicating the operative technique described by Harms and Melcher for adult patients.

Results

The mean height and width for screw entry on the posterior surface of the lateral mass were 2.6 and 8.5 mm, respectively. The mean medially angled screw trajectory from an idealized entry point on the lateral mass was 16° (range 4 to 27°). The mean maximal screw depth from this same ideal entry point was 20.3 mm. The overhang of the posterior arch averaged 6.3 mm (range 2.1–12.4 mm). The measurement between the left- and right-side lateral masses was significantly different for the maximum medially angled screw trajectory (p = 0.003) and the maximum inferiorly directed angle (p = 0.045). Those measurements in children < 8 years of age were statistically significant for the entry point height (p = 0.038) and maximum laterally angled screw trajectory (p = 0.025) compared with older children. The differences between boys and girls were statistically significant for the minimum screw length (p = 0.04) and the anterior lateral mass height (p < 0.001).

Conclusions

A significant variation in the morphological features of C-1 exists, especially between the left and right sides and in younger children. The differences between boys and girls are clinically insignificant. The critical measurement of whether the C-1 lateral mass in a child could accommodate a 3.5-mm-diameter screw is the width of the lateral mass and its proximity to the vertebral artery. Only 1 of 152 lateral masses studied would not have been able to accommodate a lateral mass screw. This study reemphasizes the importance of a preoperative CT scan of the upper cervical spine to assure safe and effective placement of the instrumentation at this level.

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Intracerebral laser interstitial thermal therapy followed by tumor resection to minimize cerebral edema

Sindhura Pisipati, Kyle A. Smith, Kushal Shah, Koji Ebersole, Roukoz B. Chamoun, and Paul J. Camarata

OBJECTIVE

Laser interstitial thermal therapy (LITT) is used in numerous neurosurgical applications including lesions that are difficult to resect. Its rising popularity can be attributed to its minimally invasive approach, improved accuracy with real-time MRI guidance and thermography, and enhanced control of the laser. One of its drawbacks is the possible development of significant edema, which contributes to extended hospital stays and often necessitates hyperosmolar or steroid therapy. Here, the authors discuss the use of minimally invasive craniotomy to resect tissue ablated with LITT in attempt to minimize cerebral edema.

METHODS

Five patients with glioblastoma multiforme prospectively underwent LITT followed by resection. The LITT was performed with the aid of an MR-compatible skull-mounted frame in the MRI suite. Ablated tumor was then resected via small craniotomy by using the NICO Myriad system or cavitron ultrasonic surgical aspirator. Postoperative management involved dexamethasone administration slowly tapered over several weeks.

RESULTS

The use of resection following LITT, as compared with open resection or LITT alone, did not extend the hospital stay except in 1 patient who required 3-day inpatient management of edema with a trapped ventricle. No new neurological deficits were encountered, although 1 patient developed seizures postoperatively. No increase in infection rates was identified.

CONCLUSIONS

Resection of ablated tumor is a viable option to reduce the incidence of neurological deficits due to edema following LITT. This approach appears to mitigate cerebral edema by increasing available volume for mass effect and reducing the tissue burden that may promote an inflammatory response.

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Spontaneous involution of Rathke cleft cysts: is it rare or just underreported?

Report of 9 cases

Hassan H. Amhaz, Roukoz B. Chamoun, Steven G. Waguespack, Komal Shah, and Ian E. McCutcheon

Rathke cleft cysts (RCCs) are benign cystic lesions of the sella that arise from the remnants of Rathke pouch. Although most are asymptomatic, symptoms can result from mass effect and commonly include headache, endocrinopathy, or visual field disturbance. Although asymptomatic patients undergo conservative treatment, patients with symptoms are typically treated surgically. The authors report 9 patients with symptomatic cystic sellar lesions and imaging characteristics consistent with an RCC; in all cases there was spontaneous involution of the lesions, and in 5 of 7 patients presenting with headache the symptom resolved. Spontaneous involution of an RCC may be more common than the paucity of prior reports would suggest, especially because the natural history of both symptomatic and asymptomatic RCCs is poorly understood. The potential for spontaneous involution, together with the clinical course of the patients reported here, supports a conservative approach for patients with symptomatic RCCs presenting solely with headache.

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Meningioma consistency prediction utilizing tumor to cerebellar peduncle intensity on T2-weighted magnetic resonance imaging sequences: TCTI ratio

Kyle A. Smith, John D. Leever, Phillip D. Hylton, Paul J. Camarata, and Roukoz B. Chamoun

OBJECTIVE

Meningioma consistency, firmness or softness as it relates to resectability, affects the difficulty of surgery and, to some degree, the extent of resection. Preoperative knowledge of tumor consistency would affect preoperative planning and instrumentation. Several methods of prediction have been proposed, but the majority lack objectivity and reproducibility or generalizability to other surgeons. In a previous pilot study of 20 patients the authors proposed a new method of prediction based on tumor/cerebellar peduncle T2-weighted imaging intensity (TCTI) ratios in comparison with objective intraoperative findings. In the present study they sought validation of this method.

METHODS

Magnetic resonance images from 100 consecutive patients undergoing craniotomy for meningioma resection were evaluated preoperatively. During surgery a consistency grade was prospectively applied to lesions by the operating surgeon, as determined by suction and/or cavitron ultrasonic surgical aspirator (CUSA) intensity. Consistency grades were A, soft; B, intermediate; and C, fibrous. Using T2-weighted MRI sequences, TCTI ratios were calculated. Analysis of the TCTI ratios and intraoperative tumor consistency was completed with ANOVA and receiver operating characteristic curves.

RESULTS

Of the 100 tumors evaluated, 50 were classified as soft, 29 as intermediate, and 21 as firm. The median TCTI ratio for firm tumors was 0.88; for intermediate tumors, 1.5; and for soft tumors, 1.84. One-way ANOVA comparing TCTI ratios for these groups was statistically significant (p < 0.0001). A single cutoff TCTI value of 1.41 for soft versus firm tumors was found to be 81.9% sensitive and 84.8% specific.

CONCLUSIONS

The authors propose this T2-based method of tumor consistency prediction with correlation to objective intraoperative consistency. This method is quantifiable and reproducible, which expands its usability. Additionally, it places tumor consistency on a graded continuum in a clinically meaningful way that could affect preoperative surgical planning.