Cerebrospinal fluid micro-volume changes inside the spinal space affect intracranial pressure in different body positions of animals and phantom.

Interpersonal differences can be observed in the human cerebrospinal fluid pressure (CSFP) in the cranium in an upright body position, varying from positive to subatmospheric values. So far, these changes have been explained by the Monroe-Kellie doctrine according to which CSFP should increase or decrease if a change in at least one of the three intracranial volumes (brain, blood, and CSF) occurs. According to our hypothesis, changes in intracranial CSFP can occur without a change in the volume of intracranial fluids. To test this hypothesis, we alternately added and removed 100 or 200 µl of fluid from the spinal CSF space of four anesthetized cats and from a phantom which, by its dimensions and biophysical characteristics, imitates the cat cerebrospinal system, subsequently comparing CSFP changes in the cranium and spinal space in both horizontal and vertical positions. The phantom was made from a rigid "cranial" part with unchangeable volume, while the "spinal" part was made of elastic material whose modulus of elasticity was in the same order of magnitude as those of spinal dura. When a fluid volume (CSF or artificial CSF) was removed from the spinal space, both lumbar and cranial CSFP pressures decreased by 2.0-2.5 cm H2O for every extracted 100 µL. On the other hand, adding fluid volume to spinal space causes an increase in both lumbar and cranial CSFP pressures of 2.6-3.0 cm H2O for every added 100 µL. Results observed in cats and phantoms did not differ significantly. The presented results on cats and a phantom suggest that changes in the spinal CSF volume significantly affect the intracranial CSFP, but regardless of whether we added or removed the CSF volume, the hydrostatic pressure difference between the measuring sites (lateral ventricle and lumbar subarachnoid space) was always constant. These results suggest that intracranial CSFP can be increased or decreased without significant changes in the volume of intracranial fluids and that intracranial CSFP changes in accordance with the law of fluid mechanics.

The Catch Mini stent retriever for mechanical thrombectomy in distal intracranial occlusions.

OBJECTIVE: Mechanical thrombectomy (MTB) is a treatment of reference for acute ischemic stroke due to large brain vessel occlusion but some concerns remain about its use in small distal branches. In the present study, we assessed the efficacy and the safety of distal MTB using the Catch Mini (CM) stent retriever. METHODS: We retrospectively reviewed a prospectively maintained database of all consecutive patients who underwent MTB for a distal intracranial occlusion with the Catch Mini device at our hospital. RESULTS: Forty-one patient underwent MTB for distal intracranial occlusions using the CM stent retriever. Good capillary reperfusion (TICT≥2b) was observed in 32 out of 41 patients (78%). Focal ischemia within the territory vascularized by the artery addressed by the CM was observed in 8 patients (19.5%). Post-procedural vasospasm was observed in 8 patients, all responding rapidly to vasodilatator administration. Two asymptomatic hemorrhages (4.9%) were noted on follow-up imaging (one patechial hemorrhage and one parenchymal hematoma) in patients with M2 occlusions. No vessel rupture were observed. Overall, good neurological outcome at three months (mRS≤2) was observed in 28 (out of 34 patients followed; 82.4%) of patients. CONCLUSIONS: Our single-center experience shows that the CM stent retriever is safe and effective for the recanalization of small diameter distal branches feeding eloquent brain areas.

Computational fluid dynamics analysis of flow reduction induced by flow-diverting stents in intracranial aneurysms: a patient-unspecific hemodynamics change perspective.

BACKGROUND AND PURPOSE: Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular aneurysms on the anterior carotid circulation. Intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. Understanding the degree of flow modification necessary to induce complete aneurysm occlusion among patients with considerable hemodynamics variability may be important for treatment planning. MATERIALS AND METHODS: Patients with incidental intracranial saccular aneurysms who underwent FDS endovascular procedures were included and studied for a 12 months' follow-up period. We used computational fluid dynamics on patient-specific geometries from 3D rotational angiography without and with virtual stent placement and thus compared intra-aneurysmal hemodynamic problems. Receiver operating characteristic analysis was used to estimate the stent:no-stent minimum hemodynamic ratio thresholds that significantly (p≤0.05) determined the condition necessary for long-term (12 months) aneurysm occlusion. RESULTS: We included 12 consecutive patients with sidewall aneurysms located in the internal carotid or vertebral artery. The measured porosity of the 12 deployed virtual FDSs was 83±3% (mean±SD). Nine aneurysms were occluded during the 12 months' follow-up, whereas three were not. A significant (p=0.05) area under the curve (AUC) was found for spatiotemporal mean velocity reduction in the aneurysms: AUC=0.889±0.113 (mean±SD) corresponding to a minimum velocity reduction threshold of 0.353 for occlusion to occur. The 95% CI of the AUC was 0.66 to 1.00. The sensitivity and specificity of the method were ∼99% and ∼67%, respectively. For both wall shear stress and pressure reductions in aneurysms no thresholds could be determined: AUC=0.63±0.16 (p=0.518) and 0.67±0.165 (p=0.405), respectively. CONCLUSIONS: For successful FDS treatment the post-stent average velocity in sidewall intracranial aneurysms must be reduced by at least one-third from the initial pre-stent conditions.

Geometrical deployment for braided stent.

The prediction of flow diverter stent (FDS) implantation for the treatment of intracranial aneurysms (IAs) is being increasingly required for hemodynamic simulations and procedural planning. In this paper, a deployment model was developed based on geometrical properties of braided stents. The proposed mathematical description is first applied on idealized toroidal vessels demonstrating the stent shortening in curved vessels. It is subsequently generalized to patient specific vasculature predicting the position of the filaments along with the length and local porosity of the stent. In parallel, in-vitro and in-vivo FDS deployments were measured by contrast-enhanced cone beam CT (CBCT) in idealized and patient-specific geometries. These measurements showed a very good qualitative and quantitative agreement with the virtual deployments and provided experimental validations of the underlying geometrical assumptions. In particular, they highlighted the importance of the stent radius assessment in the accuracy of the deployment prediction. Thanks to its low computational cost, the proposed model is potentially implementable in clinical practice providing critical information for patient safety and treatment outcome assessment.

The value of protective head cap and glasses in neurointerventional radiology.

BACKGROUND: Protection of the head and eyes of the neurointerventional radiologist is a growing concern, especially after recent reports on the incidence of brain cancer among these personnel, and the revision of dose limits to the eye lens. The goal of this study was to determine typical occupational dose levels and to evaluate the efficiency of non-routine radiation protective gear (protective eyewear and cap). Experimental correlations between the dosimetric records of each measurement point and kerma area product (KAP), and between whole body doses and eye lens doses were investigated. METHODS: Measurements were taken using thermoluminescent dosimeters placed in plastic bags and worn by the staff at different places. To evaluate the effective dose, whole body dosimeters (over and under the lead apron) were used. RESULTS: The mean annual effective dose was estimated at 0.4 mSv. Annual eye lens exposure was estimated at 17 mSv when using a ceiling shield but without protective glasses. The protective glasses reduced the eye lens dose by a factor of 2.73. The mean annual dose to the brain was 12 mSv; no major reduction was observed when using the cap. The higher correlation coefficients with KAP were found for the dosimeters positioned between the eyes (R(2)=0.84) and above the apron, and between the eye lens (R(2)=0.85) and the whole body. CONCLUSIONS: Under the specific conditions of this study, the limits currently applicable were respected. If a new eye lens dose limit is introduced, our results indicate it could be difficult to comply with, without introducing additional protective eyewear.

New Pipeline Flex device: initial experience and technical nuances.

BACKGROUND: Flow diverter stents (FDS) have been described as a breakthrough in the treatment of intracranial aneurysms. Of the various flow diverter models, the Pipeline device has been the main approved and used device, with established and good long-term results. OBJECTIVE: To present the first series of patients treated with its new version, the Pipeline Flex device. This has kept the same device design and configuration but redesigned and completely modified the delivery system. METHODS: In this technical report, we include 10 consecutive patients harboring 12 saccular aneurysms of the anterior circulation. We report the main changes on the system, immediate results, and technical nuances with illustrative cases. RESULTS: We implanted 12 devices, including 11 Pipeline Flex and one Pipeline device. We used the old version in one case that required a second layer with a short length not available in the Pipeline Flex size range. All attempts at treatment were successful and no device was discharged or removed. Recovery was required or used in half of the cases with good or excellent performance, except in one case that presented with multiple proximal loops and tight curves. We had two transitory events without ischemic lesions on MRI that recovered 1 and 4 h after all patients were discharged home asymptomatic. CONCLUSIONS: Pipeline Flex represents a major advance in FDS technology. The redesigned system has significantly improved the deployment of the Pipeline stent, by enabling the operator to resheath the device. It has the potential to continue revolutionizing the endovascular approach for intracranial aneurysms.

Assessment of intra-aneurysmal flow modification after flow diverter stent placement with four-dimensional flow MRI: a feasibility study.

BACKGROUND: Flow diverter stents (FDS) have been effectively used for the endovascular treatment of sidewall intracranial aneurysms (IAs). Unlike standard endovascular treatments used to exclude directly the aneurysm bulge from the parent vessel, FDS induce reduction in the intra-aneurysmal flow and promote progressive and stable thrombosis therein. The advent of FDS has therefore increased the need for understanding of IA hemodynamics. METHODS: We proposed the use of the most recently evolved four-dimensional (4D) flow MRI technique to evaluate qualitatively and quantitatively post-FDS flow modification in 10 patients. We report intra-aneurysmal velocity measurements and the influence of metal artifacts induced by the stent. RESULTS: An index was defined to quantitatively measure flow changes-namely, the proportional velocity reduction ratio (PVRR)-with ranges from 34.6% to 71.1%. Furthermore, we could compare streamlines characterizing the post-stent flow patterns in five patients in whom the intra-aneurysmal velocity was beyond the visualization threshold of 7.69 cm/s. CONCLUSIONS: Despite metal artifacts and the low velocities involved, 4D flow MRI could be of interest to measure qualitatively and quantitatively flow changes in stented aneurysms. However, further enhancements are required together with further validation work before it can be considered for clinical use.

The influence of body position on cerebrospinal fluid pressure gradient and movement in cats with normal and impaired craniospinal communication.

Intracranial hypertension is a severe therapeutic problem, as there is insufficient knowledge about the physiology of cerebrospinal fluid (CSF) pressure. In this paper a new CSF pressure regulation hypothesis is proposed. According to this hypothesis, the CSF pressure depends on the laws of fluid mechanics and on the anatomical characteristics inside the cranial and spinal space, and not, as is today generally believed, on CSF secretion, circulation and absorption. The volume and pressure changes in the newly developed CSF model, which by its anatomical dimensions and basic biophysical features imitates the craniospinal system in cats, are compared to those obtained on cats with and without the blockade of craniospinal communication in different body positions. During verticalization, a long-lasting occurrence of negative CSF pressure inside the cranium in animals with normal cranio-spinal communication was observed. CSF pressure gradients change depending on the body position, but those gradients do not enable unidirectional CSF circulation from the hypothetical site of secretion to the site of absorption in any of them. Thus, our results indicate the existence of new physiological/pathophysiological correlations between intracranial fluids, which opens up the possibility of new therapeutic approaches to intracranial hypertension.

Effect of head position on cerebrospinal fluid pressure in cats: comparison with artificial model.

AIM: To demonstrate that changes in the cerebrospinal fluid (CSF) pressure in the cranial cavity and spinal canal after head elevation from the horizontal level occur primarily due to the biophysical characteristics of the CSF system, ie, distensibility of the spinal dura. METHODS: Experiments in vivo were performed on cats and a new artificial model of the CSF system with dimensions similar to the CSF system in cats, consisting of non-distensible cranial and distensible spinal part. Measurements of the CSF pressure in the cranial and spinal spaces were performed in chloralose-anesthetized cats (n = 10) in the horizontal position on the base of a stereotaxic apparatus (reference zero point) and in the position in which the head was elevated to 5 cm and 10 cm above that horizontal position. Changes in the CSF pressure in the cranial and spinal part of the model were measured in the cranial part positioned in the same way as the head in cats (n = 5). RESULTS: When the cat was in the horizontal position, the values of the CSF pressure in the cranial (11.9 +/- 1.1 cm H2O) and spinal (11.8 +/- 0.6 cm H2O) space were not significantly different. When the head was elevated 5 cm or 10 cm above the reference zero point, the CSF pressure in the cranium significantly decreased to 7.7 +/- 0.6 cm H2O and 4.7 +/- 0.7 cm H2O, respectively, while the CSF pressure in the spinal space significantly increased to 13.8 +/- 0.7 cm H2O and 18.5 +/- 1.6 cm H2O, respectively (P<0.001 for both). When the artificial CSF model was positioned in the horizontal level and its cranial part elevated by 5 cm and 10 cm, the changes in the pressure were the same as those in the cats when in the same hydrostatic position. CONCLUSIONS: The new model of the CSF system used in our study faithfully mimicked the changes in the CSF pressure in cats during head elevation in relation to the body. Changes in the pressure in the model were not accompanied by the changes in fluid volume in the non-distensible cranial part of the model. Thus, it seems that the changes in the CSF pressure occur due to the biophysical characteristics of the CSF system rather than the displacement of the blood and CSF volumes from the cranium to the lower part of body.