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Dale Ding and Kenneth C. Liu

Intracranial atherosclerosis presents a therapeutic challenge to medical and surgical physicians alike. Despite maximal medical therapy, the stroke rate from this disease is still high, especially when arterial stenosis is severe and patients are symptomatic. Open surgical therapy has yet to be shown to be a more efficacious treatment than medical therapy alone, largely due to the relatively high rates of perioperative complications. Angioplasty has a similar fate, with the risk of periprocedural complications outweighing the overall benefit of treatment. With the advent of stents for use in intracranial vasculature, new hope has arisen for the treatment of intracranial atherosclerosis. The NEUROLINK system, the drug-eluting stents Taxus and Cypher, the flexible Wingspan stent, the Apollo stent, and the Pharos stent have all been used in various prospective and retrospective clinical studies with varying technical and clinical results. The authors' objective is to review and loosely compare the data presented for each of these stenting systems. While the Wingspan stent appears to have somewhat of an advantage with regard to technical success in comparison with the other stenting systems, the clinical follow-up time of its studies is too short to properly compare its complication rates with those of other stents. Before we continue to move forward with stenting for intracranial stenosis, a randomized prospective trial is ultimately needed to directly compare intracranial stenting to medical therapy.

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Aaron E. Bond, John A. Jane Sr., Kenneth C. Liu, and Edward H. Oldfield

OBJECT

The authors completed a prospective, institutional review board–approved study using intraoperative MRI (iMRI) in patients undergoing posterior fossa decompression (PFD) for Chiari I malformation. The purpose of the study was to examine the utility of iMRI in determining when an adequate decompression had been performed.

METHODS

Patients with symptomatic Chiari I malformations with imaging findings of obstruction of the CSF space at the foramen magnum, with or without syringomyelia, were considered candidates for surgery. All patients underwent complete T1, T2, and cine MRI studies in the supine position preoperatively as a baseline. After the patient was placed prone with the neck flexed in position for surgery, iMRI was performed. The patient then underwent a bone decompression of the foramen magnum and arch of C-1, and the MRI was repeated. If obstruction was still present, then in a stepwise fashion the patient underwent dural splitting, duraplasty, and coagulation of the tonsils, with an iMRI study performed after each step guiding the decision to proceed further.

RESULTS

Eighteen patients underwent PFD for Chiari I malformations between November 2011 and February 2013; 15 prone preincision iMRIs were performed. Fourteen of these patients (93%) demonstrated significant improvement of CSF flow through the foramen magnum dorsal to the tonsils with positioning only. This improvement was so notable that changes in CSF flow as a result of the bone decompression were difficult to discern.

CONCLUSIONS

The authors observed significant CSF flow changes when simply positioning the patient for surgery. These results put into question intraoperative flow assessments that suggest adequate decompression by PFD, whether by iMRI or intraoperative ultrasound. The use of intraoperative imaging during PFD for Chiari I malformation, whether by ultrasound or iMRI, is limited by CSF flow dynamics across the foramen magnum that change significantly when the patient is positioned for surgery.

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Susan R. Durham, Kenneth C. Liu, and Nathan R. Selden

Object

The purpose of this study was to evaluate the risk of progression of traumatic intracranial lesions in children by comparing initial and subsequent computed tomography (CT) scans. Reserving repeated CT imaging for patients who harbor higher-risk lesions may reduce overall radiation exposure, the need for sedative agents, and cost.

Methods

The authors performed a retrospective cohort study in 268 patients younger than 18 years of age who underwent repeated CT scanning within 24 hours of their initial CT scanning procedure. The risk of progression between the initial and repeated CT scanning sessions and the need for delayed neurosurgical intervention were determined for each lesion type.

In 54 patients (20.1%) the normal findings on the initial CT study did not change on subsequent imaging. In 61 (28.5%) of the 214 patients in whom abnormal findings were present on the initial scan, progression was demonstrated. Patients with epidural hematoma (EDH; odds ratio [OR] 12.29), subdural hematoma (SDH; OR 3.18), cerebral edema (OR 9.34), and intraparenchymal hemorrhage (IPH; OR 18.3) were found to be at a significantly increased risk for progression and to require delayed neurosurgical intervention (OR 11.91). No significantly increased risk was found for patients with subarachnoid hemorrhage (SAH), intraventricular hemorrhage (IVH), diffuse axonal injury (DAI), or skull fracture.

Conclusions

Repeated CT imaging in children with high-risk lesions such as EDH, SDH, cerebral edema, and IPH is recommended. However, in children with low-risk lesions, such as SAH, IVH, DAI, and isolated skull fractures but no sign of clinical deterioration, repeated imaging may be less likely to alter the clinical management scheme. The limited benefits of undertaking repeated imaging in these patients should be weighed against the risks of radiation exposure, sedation, intrahospital transportation, and patient monitoring.

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Thomas J. Buell, Daniel M. S. Raper, I. Jonathan Pomeraniec, Dale Ding, Ching-Jen Chen, Davis G. Taylor, and Kenneth C. Liu

Stenosis of the transverse sinus (TS) and sigmoid sinus (SS), with a trans-stenosis pressure gradient, has been implicated in the pathophysiology of idiopathic intracranial hypertension (IIH). MRI has shown improvement in TS and SS stenosis after high-volume lumbar puncture (HVLP) in a subset of patients with IIH. The authors present the first report of an IIH patient with immediate post-HVLP TS and SS trans-stenosis pressure gradient reduction and an attendant increase in TS and SS cross-sectional area confirmed using intravascular ultrasonography (IVUS). Recurrence of the patient’s TS-SS stenosis coincided with elevated HVLP opening pressure, and venous sinus stent placement resulted in clinical improvement. This report suggests that TS and SS stenosis may be a downstream effect of elevated intracranial pressure in IIH, rather than its principal etiological mechanism. However, the authors hypothesize that endovascular stenting may obliterate a positive feedback loop involving trans-stenosis pressure gradients, and still benefit appropriately selected patients.

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I. Jonathan Pomeraniec, Dale Ding, Robert M. Starke, Kenneth C. Liu, E. Kelly Mrachek, M. Beatriz Lopes, and Jason P. Sheehan

OBJECTIVE

Stereotactic radiosurgery (SRS) is a commonly employed treatment modality for brain arteriovenous malformations (AVMs). However, due to the low frequency of delayed cyst formation after AVM SRS, as well as the prolonged time interval between treatment and its occurrence, the characteristics of post-SRS cyst formation are not well defined. Therefore, the aims of this retrospective cohort study are to determine the rate of cyst formation after SRS for AVMs, identify predictive factors, and evaluate the clinical sequelae of post-SRS cysts.

METHODS

The authors analyzed an SRS database for AVM patients who underwent SRS at the University of Virginia and identified those who developed post-SRS cysts. Statistical analyses were performed to determine predictors of post-SRS cyst formation and the effect of cyst formation on new or worsening seizures after SRS.

RESULTS

The study cohort comprised 1159 AVM patients treated with SRS; cyst formation occurred in 17 patients (post-SRS cyst rate of 1.5%). Compared with patients who did not develop post-SRS cysts, those with cyst formation were treated with a greater number of radiosurgical isocenters (mean 3.8 vs 2.8, p = 0.047), had a longer follow-up (mean 132 vs 71 months, p < 0.001), were more likely to develop radiological radiation-induced changes (RIC) (64.7% vs 36.1%, p = 0.021), and had a longer duration of RIC (57 vs 21 months, p < 0.001). A higher number of isocenters (p = 0.014), radiological RIC (p = 0.002), and longer follow-up (p = 0.034) were found to be independent predictors of post-SRS cyst formation in the multivariate analysis. There was a trend toward a significant association between cyst formation and new or worsening seizures in univariate analysis (p = 0.054).

CONCLUSIONS

Patients with greater nidal complexity appear to be more prone to post-SRS cyst formation. The findings of this study emphasize the importance of long-term follow-up for patients who have undergone AVM SRS, even after nidal obliteration is achieved. Post-SRS cysts may be epileptogenic, although seizure outcomes after AVM SRS are multifactorial.

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Kenneth C. Liu, Robert M. Starke, Christopher R. Durst, Tony R. Wang, Dale Ding, R. Webster Crowley, and Steven A. Newman

OBJECTIVE

Idiopathic intracranial hypertension (IIH) may cause blindness due to elevated intracranial pressure (ICP). Venous sinus stenosis has been identified in select patients, leading to stenting as a potential treatment, but its effects on global ICP have not been completely defined. The purpose of this pilot study was to assess the effects of venous sinus stenting on ICP in a small group of patients with IIH.

METHODS

Ten patients for whom medical therapy had failed were prospectively followed. Ophthalmological examinations were assessed, and patients with venous sinus stenosis on MR angiography proceeded to catheter angiography, venography with assessment of pressure gradient, and ICP monitoring. Patients with elevated ICP measurements and an elevated pressure gradient across the stenosis were treated with stent placement.

RESULTS

All patients had elevated venous pressure (mean 39.5 ± 14.9 mm Hg), an elevated gradient across the venous sinus stenosis (30.0 ± 13.2 mm Hg), and elevated ICP (42.2 ± 15.9 mm Hg). Following stent placement, all patients had resolution of the stenosis and gradient (1 ± 1 mm Hg). The ICP values showed an immediate decrease (to a mean of 17.0 ± 8.3 mm Hg), and further decreased overnight (to a mean of 8 ± 4.2 mm Hg). All patients had subjective and objective improvement, and all but one improved during follow-up (median 23.4 months; range 15.7–31.6 months). Two patients developed stent-adjacent stenosis; retreatment abolished the stenosis and gradient in both cases. Patients presenting with papilledema had resolution on follow-up funduscopic imaging and optical coherence tomography (OCT) and improvement on visual field testing. Patients presenting with optic atrophy had optic nerve thinning on follow-up OCT, but improved visual fields.

CONCLUSIONS

For selected patients with IIH and venous sinus stenosis with an elevated pressure gradient and elevated ICP, venous sinus stenting results in resolution of the venous pressure gradient, reduction in ICP, and functional, neurological, and ophthalmological improvement. As patients are at risk for stent-adjacent stenosis, further follow-up is necessary to determine long-term outcomes and gain an understanding of venous sinus stenosis as a primary or secondary pathological process behind elevated ICP.

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Dale Ding, Robert M. Starke, Christopher R. Durst, R. Webster Crowley, and Kenneth C. Liu

Increasing evidence supports dural venous sinus stenosis as the patho-etiology of pseudotumor cerebri (PTC) in a subset of affected patients. In this video, we demonstrate our technique for 1) diagnostic venous manometry to identify a flow-limiting stenosis of the transverse sinus in a PTC patient; and 2) successful treatment of the patient with venous stenting across the structural and physiological stricture in the dural sinus. The pressure gradient decreased from 20 mmHg pre-stent to 3 mmHg post-stent. In order to further quantify the effect of our intervention, concurrent intracranial pressure monitoring was performed.

The video can be found here: http://youtu.be/auxRg17F8yI.

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Robert M. Starke, Dale Ding, Christopher R. Durst, R. Webster Crowley, and Kenneth C. Liu

Dissecting vertebral artery (VA) aneurysms are difficult to obliterate when the parent artery cannot be safely occluded. In this video, we demonstrate a combined microsurgical and endovascular treatment technique for a ruptured, dissecting VA aneurysm incorporating the origin of the posterior inferior cerebellar artery (PICA). We first performed a PICA-PICA side-to-side bypass to preserve flow through the right PICA. An endovascular approach was then utilized to embolize the proximal portion of the aneurysm from the right VA and the distal portion of the aneurysm from the left VA.

The video can be found here: http://youtu.be/dkkKsX2BiJI.

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Frank P. K. Hsu, Gregory J. Anderson, Aclan Dogan, Joseph Finizio, Akio Noguchi, Kenneth C. Liu, Sean O. McMenomey, and Johnny B. Delashaw Jr.

Object. Conventional wisdom regarding skull base surgery says that more extensive bone removal equals greater exposure. Few researchers have quantitatively examined this assertion, however. In this study the authors used a frameless stereotactic system to measure quantitatively the area of petroclival exposure and surgical freedom for manipulation of instruments with successive steps of temporal bone removal.

Methods. With the aid of high-power magnification and a high-speed drill, 12 cadaveric specimens were dissected in four predetermined, successive bone removal steps: 1) removal of the Kawase triangle; 2) removal of the Glasscock triangle; 3) removal of the cochlea together with skeletonization of the anterior internal auditory canal; and 4) inferior displacement of the zygoma.

Step 1 offered 62 ± 43 mm2 of exposed petroclival area, with 84 ± 69 mm2 of surgical freedom; Step 2, 61 ± 22 and 76 ± 58 mm2; Step 3, 128 ± 47 and 109 ± 87 mm2; and Step 4, 135 ± 38 and 102 ± 69 mm2, respectively.

Conclusions. The middle fossa approach provided a means surgically to expose the petroclival area. When examined quantitatively by using a frameless stereotactic device, the authors determined that the removal of the cochlea and skeletonization of the anterior internal auditory canal (Step 3) provided the most significant increase in both exposure and surgical freedom. Removal of the zygoma improved neither exposure nor surgical freedom.