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Free access

Zsolt Zador, David J. Coope and Ian D. Kamaly-Asl

OBJECT

Endoscopic third ventriculostomy (ETV) has become a widely used method for CSF diversion when treating obstructive hydrocephalus. There are multiple recommendations on the transcortical ETV entry points, and some are specifically designed to provide a trajectory that avoids displacement to the eloquent periventricular structures. However, the morphology of the ventricular system is highly variable in hydrocephalus, and therefore a single best ETV trajectory may not be applicable to all cases. In the current study, 3 frequently quoted ETV entry points are compared in a cohort of pediatric cases with different degrees of ventriculomegaly.

METHODS

The images of 30 consecutive pediatric patients with varying degrees of ventriculomegaly were reviewed. Three-dimensional models were created using radiological analysis of anatomical detail and preoperative MRI scans in order to simulate 3 frequently quoted ETV trajectories for rigid neuroendoscopes. These trajectories were characterized based on the frequency and depth of tissue displacement to structures such as the fornix, caudate nucleus, genu of the internal capsule, and thalamus. The results are stratified based on ventricle size using the frontal horn ratio (FHR).

RESULTS

Eloquent areas were displaced in nearly all analyzed entry points (97%–100%). Stratifying the data based on ventricle size revealed that 1) lateral structures were more likely to be displaced in cases of intermediate ventriculomegaly (FHR < 0.4) using all 3 trajectories, whereas 2) the fornix was less likely to be displaced using more posteriorly placed trajectories for severe ventriculomegaly (FHR > 0.4). Allowing for minimal (2.4 mm) tissue displacement, a more posterior entry point was less traumatic for severe ventriculomegaly.

CONCLUSIONS

There is no single best ETV trajectory that fully avoids displacement of the eloquent periventricular structures. Larger ventricles require a more posteriorly placed entry point in order to reduce injury to the eloquent structures, and intermediate ventricles would dictate a medial entry point. These results suggest that the optimal entry point should be selected on a case-by-case basis after incorporating ventricle size.

Open access

Daniel Lewis, Carmine A. Donofrio, Claire O’Leary, Ka-loh Li, Xiaoping Zhu, Ricky Williams, Ibrahim Djoukhadar, Erjon Agushi, Cathal J. Hannan, Emma Stapleton, Simon K. Lloyd, Simon R. Freeman, Andrea Wadeson, Scott A. Rutherford, Charlotte Hammerbeck-Ward, D. Gareth Evans, Alan Jackson, Omar N. Pathmanaban, Federico Roncaroli, Andrew T. King and David J. Coope

OBJECTIVE

Inflammation and angiogenesis may play a role in the growth of sporadic and neurofibromatosis type 2 (NF2)–related vestibular schwannoma (VS). The similarities in microvascular and inflammatory microenvironment have not been investigated. The authors sought to compare the tumor microenvironment (TME) in sporadic and NF2-related VSs using a combined imaging and tissue analysis approach.

METHODS

Diffusion MRI and high-temporal-resolution dynamic contrast-enhanced (DCE) MRI data sets were prospectively acquired in 20 NF2-related and 24 size-matched sporadic VSs. Diffusion metrics (mean diffusivity, fractional anisotropy) and DCE-MRI–derived microvascular biomarkers (transfer constant [Ktrans], fractional plasma volume, tissue extravascular-extracellular space [ve], longitudinal relaxation rate, tumoral blood flow) were compared across both VS groups, and regression analysis was used to evaluate the effect of tumor size, pretreatment tumor growth rate, and tumor NF2 status (sporadic vs NF2-related) on each imaging parameter. Tissues from 17 imaged sporadic VSs and a separate cohort of 12 NF2-related VSs were examined with immunohistochemistry markers for vessels (CD31), vessel permeability (fibrinogen), and macrophage density (Iba1). The expression of vascular endothelial growth factor (VEGF) and VEGF receptor 1 was evaluated using immunohistochemistry, Western blotting, and double immunofluorescence.

RESULTS

Imaging data demonstrated that DCE-MRI–derived microvascular characteristics were similar in sporadic and NF2-related VSs. Ktrans (p < 0.001), ve (p ≤ 0.004), and tumoral free water content (p ≤ 0.003) increased with increasing tumor size and pretreatment tumor growth rate. Regression analysis demonstrated that with the exception of mean diffusivity (p < 0.001), NF2 status had no statistically significant effect on any of the imaging parameters or the observed relationship between the imaging parameters and tumor size (p > 0.05). Tissue analysis confirmed the imaging metrics among resected sporadic VSs and demonstrated that across all VSs studied, there was a close association between vascularity and Iba1+ macrophage density (r = 0.55, p = 0.002). VEGF was expressed by Iba1+ macrophages.

CONCLUSIONS

The authors present the first in vivo comparative study of microvascular and inflammatory characteristics in sporadic and NF2-related VSs. The imaging and tissue analysis results indicate that inflammation is a key contributor to TME and should be viewed as a therapeutic target in both VS groups.