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Martin M. Tisdall, Richard D. Hayward and Dominic N. P. Thompson

OBJECT

A dermal sinus tract is a common form of occult spinal dysraphism. The presumed etiology relates to a focal failure of disjunction resulting in a persistent adhesion between the neural and cutaneous ectoderm. Clinical and radiological features can appear innocuous, leading to delayed diagnosis and failure to appreciate the implications or extent of the abnormality. If it is left untreated, complications can include meningitis, spinal abscess, and inclusion cyst formation. The authors present their experience in 74 pediatric cases of spinal dermal tract in an attempt to identify which clinical and radiological factors are associated with an infective presentation and to assess the reliability of MRI in evaluating this entity.

METHODS

Consecutive cases of spinal dermal tract treated with resection between 1998 and 2010 were identified from the departmental surgical database. Demographics, clinical history, and radiological and operative findings were collected from the patient records. The presence or absence of active infection (abscess, meningitis) at the time of neurosurgical presentation and any history of local sinus discharge or infection was assessed. Magnetic resonance images were reviewed to evaluate the extent of the sinus tract and determine the presence of an inclusion cyst. Radiological and operative findings were compared.

RESULTS

The surgical course was uncomplicated in 90% of 74 cases eligible for analysis. Magnetic resonance imaging underreported the presence of both an intradural tract (MRI 46%, operative finding 86%) and an intraspinal inclusion cyst (MRI 15%, operative finding 24%). A history of sinus discharge (OR 12.8, p = 0.0003) and the intraoperative identification of intraspinal inclusion cysts (OR 5.6, p = 0.023) were associated with an infective presentation. There was no significant association between the presence of an intradural tract discovered at surgery and an infective presentation.

CONCLUSIONS

Surgery for the treatment of spinal dermal tract carries a low morbidity. While it seems intuitive that tracts without intradural extension carry a low risk of spinal cord tethering, it is not possible to reliably detect these cases using MRI. Similarly, intraspinal dermoid cannot be reliably excluded using MRI and carries an increased risk of infection. These points justify excision together with intradural exploration of all spinal dermal sinus tracts.

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Juan F. Martínez-Lage

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Julia D. Sharma, Kiran K. Seunarine, Muhammad Zubair Tahir and Martin M. Tisdall

OBJECTIVE

The aim of this study was to compare the accuracy of optical frameless neuronavigation (ON) and robot-assisted (RA) stereoelectroencephalography (SEEG) electrode placement in children, and to identify factors that might increase the risk of misplacement.

METHODS

The authors undertook a retrospective review of all children who underwent SEEG at their institution. Twenty children were identified who underwent stereotactic placement of a total of 218 electrodes. Six procedures were performed using ON and 14 were placed using a robotic assistant. Placement error was calculated at cortical entry and at the target by calculating the Euclidean distance between the electrode and the planned cortical entry and target points. The Mann-Whitney U-test was used to compare the results for ON and RA placement accuracy. For each electrode placed using robotic assistance, extracranial soft-tissue thickness, bone thickness, and intracranial length were measured. Entry angle of electrode to bone was calculated using stereotactic coordinates. A stepwise linear regression model was used to test for variables that significantly influenced placement error.

RESULTS

Between 8 and 17 electrodes (median 10 electrodes) were placed per patient. Median target point localization error was 4.5 mm (interquartile range [IQR] 2.8–6.1 mm) for ON and 1.07 mm (IQR 0.71–1.59) for RA placement. Median entry point localization error was 5.5 mm (IQR 4.0–6.4) for ON and 0.71 mm (IQR 0.47–1.03) for RA placement. The difference in accuracy between Stealth-guided (ON) and RA placement was highly significant for both cortical entry point and target (p < 0.0001 for both). Increased soft-tissue thickness and intracranial length reduced accuracy at the target. Increased soft-tissue thickness, bone thickness, and younger age reduced accuracy at entry. There were no complications.

CONCLUSIONS

RA stereotactic electrode placement is highly accurate and is significantly more accurate than ON. Larger safety margins away from vascular structures should be used when placing deep electrodes in young children and for trajectories that pass through thicker soft tissues such as the temporal region.

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M. Ross Bullock

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Martin M. Tisdall, Ilias Tachtsidis, Terence S. Leung, Clare E. Elwell and Martin Smith

Object

Traumatic brain injury (TBI) is associated with depressed aerobic metabolism and mitochondrial dysfunction. Normobaric hyperoxia (NBH) has been suggested as a treatment for TBI, but studies in humans have produced equivocal results. In this study the authors used brain tissue O2 tension measurement, cerebral microdialysis, and near-infrared spectroscopy to study the effects of NBH after TBI. They investigated the effects on cellular and mitochondrial redox states measured by the brain tissue lactate/pyruvate ratio (LPR) and the change in oxidized cytochrome c oxidase (CCO) concentration, respectively.

Methods

The authors studied 8 adults with TBI within the first 48 hours postinjury. Inspired oxygen percentage at normobaric pressure was increased from baseline to 60% for 60 minutes and then to 100% for 60 minutes before being returned to baseline for 30 minutes.

Results

The results are presented as the median with the interquartile range in parentheses. During the 100% inspired oxygen percentage phase, brain tissue O2 tension increased by 7.2 kPa (range 4.5–9.6 kPa) (p < 0.0001), microdialysate lactate concentration decreased by 0.26 mmol/L (range 0.0–0.45 mmol/L) (p = 0.01), microdialysate LPR decreased by 1.6 (range 1.0–2.3) (p = 0.02), and change in oxidized CCO concentration increased by 0.21 μmol/L (0.13–0.38 μmol/L) (p = 0.0003). There were no significant changes in intracranial pressure or arterial or microdialysate glucose concentration. The change in oxidized CCO concentration correlated with changes in brain tissue O2 tension (rs= 0.57, p = 0.005) and in LPR (rs= −0.53, p = 0.006).

Conclusions

The authors have demonstrated oxidation in cerebral cellular and mitochondrial redox states during NBH in adults with TBI. These findings are consistent with increased aerobic metabolism and suggest that NBH has the potential to improve outcome after TBI. Further studies are warranted.

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Aswin Chari, Martin M. Tisdall and Hani J. Marcus