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  • Author or Editor: Keith E. Aronyk x
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Jeffrey A. Pugh, Keith E. Aronyk and Jonathan A. Norton

Object

The authors conducted a study to determine the neurophysiological capacity of the neural placode in spina bifida neonates and to determine if the spinal nerve roots in these neonates had normal stimulation.

Methods

The authors present a case series of 2 neonates born with open neural tube defects who underwent neural tube closure within 24 hours of birth. Neurophysiological monitoring and electrical stimulation of the placode and nerve roots was performed before and after closure of the neural tube.

Results

Stimulation of nerve roots resulted in evoked electromyographic responses in distinct muscle groups, indicative of the myotome innervation pattern. Stimulation threshold did not change significantly after closure of the placode. Stimulation within the placode generated an alternating pattern of activity in the left and right legs.

Conclusions

Closure of the neural tube did not affect the stimulation threshold of the nerve roots, which remained easily excitable. The viability of the nerve roots suggests that they may be candidates for neural prostheses in the future. The neural placode contains basic neural elements for generating a locomotor-like pattern in response to tonic neural inputs.

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Kelly D. Johnston, Anil H. Walji, Richard J. Fox, Jeffrey A. Pugh and Keith E. Aronyk

Object

The purpose of this human cadaver study was to determine whether or not an intraosseous skull infusion would access the superior sagittal sinus (SSS) via intradural venous channels. The diploic space of the skull bone contains a sinusoidal vascular network that communicates with the underlying dura mater. Diploic veins in the parasagittal area connect with endothelium-lined intradural channels in the subjacent dura and ultimately with the dural venous sinuses. A significant proportion of cerebrospinal fluid (CSF) absorption is thought to occur via arachnoid granulations in the region of the SSS and especially along the parasagittal dura where arachnoid granulations are surrounded by intradural venous channels (lateral lacunae). The CSF is likely to be conducted from the subarachnoid space into the venous system via the fine intradural channels making up the lateral lacunae.

Methods

Infusion of vinyl acetate casting material into the diploic space of the human cadaveric skull resulted in complete filling of the lateral lacunae and SSS. Corrosion casting techniques and examination under magnification were used to characterize the anatomical connections between diploic spaces and dural venous sinuses.

Results

Corrosion casting, performed on five formalin-fixed cadavers, clearly showed the anatomical connections between the diploic infusion site and the venous sinuses in the underlying parasagittal dura where some of the CSF is thought to be absorbed.

Conclusions

The diploic vascular channels of the human skull may represent an indirect pathway into the dural venous sinuses. Intraosseous skull infusion may represent another possible strategy for diversion of CSF into the vascular system in the treatment of hydrocephalus.

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Alexander Zouros, Ravi Bhargava, Michael Hoskinson and Keith E. Aronyk

✓ Bilateral convexity and interhemispheric subdural hematomas are common neuroimaging patterns seen in infants who have sustained nonaccidental head injuries (NAHIs). These collections often appear aschronic or acute-on-chronic on computerized tomography (CT) studies. To determine the nature of these extraaxial fluid collections and their relationship to cerebrospinal fluid (CSF) dynamics, the authors studied five infants with suspected NAHI in whom symptomatic bilateral mixed- or low-density subdural collections were revealed on imaging studies; the patients underwent burr hole evacuation of the hematoma and external drainage. Once decompression was achieved, radiotracer was injected into the lumbar subarachnoid space, and the subdural drainage system was monitored for appearance of the isotope. In all five cases, the radiotracer moved rapidly from the lumbar subarachnoid space into the convexity subdural space and then into the external drainage system. This indicated the possibility that some of these mixed-density subdural collections were acute blood mixed with CSF rather than acute-on-chronic collections arising from rebleeding subdural membranes. The authors propose that, during infancy, tears in the loosely adherent arachnoid envelope at the main arachnoid granulation site along the superior sagittal sinus may result in a considerable amount of CSF mixing with acute blood in the subdural space, creating a hematohygroma.

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Cameron A. Elliott, Hayden Danyluk, Keith E. Aronyk, Karolyn Au, B. Matt Wheatley, Donald W. Gross, Tejas Sankar and Christian Beaulieu

OBJECTIVE

Diffusion tensor imaging (DTI) tractography is commonly used in neurosurgical practice but is largely limited to the preoperative setting. This is due primarily to image degradation caused by susceptibility artifact when conventional single-shot (SS) echo-planar imaging (EPI) DTI (SS-DTI) is acquired for open cranial, surgical position intraoperative DTI (iDTI). Readout-segmented (RS) EPI DTI (RS-DTI) has been reported to reduce such artifact but has not yet been evaluated in the intraoperative MRI (iMRI) environment. The authors evaluated the performance of RS versus SS EPI for DTI of the human brain in the iMRI setting.

METHODS

Pre- and intraoperative 3-T 3D T1-weighted and 2D multislice RS-iDTI (called RESOLVE [readout segmentation of long variable echo-trains] on the Siemens platform) and SS-iDTI images were acquired in 22 adult patients undergoing intraaxial iMRI resections for suspected low-grade glioma (14; 64%), high-grade glioma (7; 32%), or focal cortical dysplasia. Regional susceptibility artifact, anatomical deviation relative to T1-weighted imaging, and tractographic output for surgically relevant tracts were compared between iDTI sequences as well as the intraoperative tract shifts from preoperative DTI.

RESULTS

RS-iDTI resulted in qualitatively less regional susceptibility artifact (resection cavity, orbitofrontal and anterior temporal cortices) and mean anatomical deviation in regions most prone to susceptibility artifact (RS-iDTI 2.7 ± 0.2 vs SS-iDTI 7.5 ± 0.4 mm) compared to SS-iDTI. Although tract reconstruction success did not significantly differ by DTI method, susceptibility artifact–related tractography failure (of at least 1 surgically relevant tract) occurred for SS-iDTI in 8/22 (36%) patients, and in 5 of these 8 patients RS-iDTI permitted successful reconstruction. Among cases with successful tractography for both sequences, maximal intersequence differences were substantial (mean 9.5 ± 5.7 mm, range −27.1 to 18.7 mm).

CONCLUSIONS

RS EPI enables higher quality and more accurate DTI for surgically relevant tractography of major white matter tracts in intraoperative, open cranium neurosurgical applications at 3 T.

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Mitchell P. Wilson, Keith E. Aronyk, Thomas Yeo, Michael Chow and Jeffrey A. Pugh

Spinal arteriovenous malformations are rare in children, although perimedullary arteriovenous fistulas (PMAVFs) may account for up to 24% of spinal arteriovenous malformations in this age group. Reported presentations of PMAVFs have included progressive or acute myelopathic symptoms, pain, hematomyelia, and subarachnoid hemorrhage. No known reports of an unruptured PMAVF causing communicating hydrocephalus have been previously published.

A 17-month-old girl presented to the authors' clinic with a 6-month history of back and leg pain, gait regression, constipation, and marked lumbar hyperlordosis due to a PMAVF. A brain MRI study also demonstrated advanced hydrocephalus. The patient underwent embolization with Onyx of 2 feeding arteries from the right L-1 and 1 feeding artery from the left L-1 lumbar arteries. Postembolization follow-up imaging demonstrated a reduction in size of the L-1 pedicles and no residual supply of the fistula. Three-year clinical follow-up showed normal bowel and bladder function with significant improvements in the patient's back pain, gait, and hyperlordosis. The patient's ventricular enlargement improved without direct management of her hydrocephalus.

To the authors' knowledge, this is the first reported case of communicating hydrocephalus caused by an unruptured PMAVF. The authors postulate that the origin of hydrocephalus was either central venous hypertension caused by the high-flow fistula or a change in fluid dynamics reducing CSF resorption through arachnoid granulations in the lumbar region of the spinal cord. The exact role that spinal arachnoid granulations play in CSF resorption is not currently known. Regardless of pathogenesis, initial treatment should focus on management of the fistula with additional hydrocephalus management only when necessary.

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Jeffrey A. Pugh, Jonathan Tyler, Thomas A. Churchill, Richard J. Fox and Keith E. Aronyk

Object

Hydrocephalus results from abnormal cerebrospinal fluid (CSF) volumes or flow patterns. The absorption of CSF is determined largely by pressures within veins and venous sinuses in the head and adjacent to the spine. Most surgical solutions for hydrocephalus involve diversion of excess CSF into alternative absorption sites, and most of these solutions are still suboptimal. The focus of this work has been to recreate more normal CSF absorption into the dural venous sinuses without having to directly access the superior sagittal sinus (SSS).

Methods

Intraosseous skull infusion for the purpose of accessing the SSS and the systemic venous system was tested by experimental skull infusions of tracer fluids into living large animals (14 adult pigs).

Compared with control injections into an ear vein, infusions into the skull through specially designed infusion devices had similar systemic absorption characteristics. This suggested that intraosseous skull infusion in a living large animal was successful in gaining access to the SSS and systemic venous system.

Conclusions

This study constitutes the first demonstration of the success of intraosseous skull infusion in gaining rapid access to the systemic venous system and it thus opens the possibility of using this strategy for diversion of CSF back into the intracranial venous system for the treatment of hydrocephalus.