Brain Arteriovenous Malformations: The Role of Imaging in Treatment Planning and Monitoring Response

Understanding the Importance of Blood-Brain Barrier Alterations in Brain Arteriovenous Malformations and Implications for Treatment: A Dynamic Contrast-Enhanced-MRI-Based Prospective Study

BACKGROUND AND OBJECTIVES

The major clinical implication of brain arteriovenous malformations (bAVMs) is spontaneous intracranial hemorrhage. There is a growing body of experimental evidence proving that inflammation and blood-brain barrier (BBB) dysfunction are involved in both the clinical course of the disease and the risk of bleeding. However, how bAVM treatment affects perilesional BBB disturbances is yet unclear.

METHODS

We assessed the permeability changes of the BBB using dynamic contrast-enhanced MRI (DCE-MRI) in a series of bAVMs (n = 35), before and at a mean of 5 (±2) days after treatment. A set of cerebral cavernous malformations (CCMs) (n = 16) was used as a control group for the assessment of the surgical-related collateral changes. The extended Tofts pharmacokinetic model was used to extract permeability (K trans ) values in the lesional, perilesional, and normal brain tissues.

RESULTS

In patients with bAVM, the permeability of BBB was higher in the perilesional of bAVM tissue compared with the rest of the brain parenchyma (mean K trans 0.145 ± 0.104 vs 0.084 ± 0.035, P = .004). Meanwhile, no significant changes were seen in the perilesional brain of CCM cases (mean K trans 0.055 ± 0.056 vs 0.061 ± 0.026, P = .96). A significant decrease in BBB permeability was evident in the perilesional area of bAVM after surgical resection (mean K trans 0.145 ± 0.104 vs 0.096 ± 0.059, P = .037). This benefit in BBB permeability reduction after surgery seemed to surpass the relative increase in permeability inherent to the surgical manipulation.

CONCLUSION

In contrast to CCMs, BBB permeability in patients with bAVM is increased in the perilesional parenchyma, as assessed using DCE-MRI. However, bAVM surgical resection seems to reduce BBB permeability in the perilesional tissue. No evidence of the so-called breakthrough phenomenon was detected in our series. DCE-MRI could become a valuable tool to follow the longitudinal course of BBB damage throughout the natural history and clinical course of bAVMs.

Cerebral arteriovenous malformation calcifications: A systematic review, case series, and a proposed classification system

Background

Brain arteriovenous malformations (AVMs) are intracranial vascular lesions characterized by a nidus of vessels fed by an artery and drained by a vein, lacking intervening capillaries. Angiography remains the gold standard for a definitive diagnosis. There is a paucity in the literature regarding clinical presentation and management of patients with calcified cerebral AVM (cCAVM). This study aims to highlight the clinical presentation and management of patients with cCAVM and also to propose a classification of calcification patterns in cCAVMs based on brain computed tomography (CT) findings.

Methods

A systematic review using PubMed, Scopus, and Web of Science was done according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to identify cases that illustrate cCAVM. A case series was also presented to supplement the current literature.

Results

Twenty patients with cCAVM were included, with the male gender representing more than 50% of the patient population. Their age ranged from 11 to 69 years, with seizures being the most common presenting symptom. The frontal lobe was the most common location of AVMs, followed by the parietal lobe. Most (80%) of the calcifications were nidal, with the remaining being extranidal (20%).

Conclusion

The CT scans of patients displayed significant variability due to the unique characteristics of each cCAVM. To address this diversity, a novel classification system was developed to provide a comprehensive framework for understanding cCAVMs based on their location, size, and extent.

Current and Future Applications of Arterial Spin Labeling MRI in Cerebral Arteriovenous Malformations

Arterial spin labeling (ASL) has emerged as a promising noninvasive tool for the evaluation of both pediatric and adult arteriovenous malformations (AVMs). This paper reviews the advantages and challenges associated with the use of ASL in AVM assessment. An assessment of the diagnostic workup of AVMs and their variants in both adult and pediatric populations is proposed. Evaluation after treatments, whether endovascular or microsurgical, was similarly examined. ASL, with its endogenous tracer and favorable safety profile, offers functional assessment and arterial feeder identification. ASL has demonstrated strong performance in identifying feeder arteries and detecting arteriovenous shunting, although some studies report inferior performance compared with digital subtraction angiography (DSA) in delineating venous drainage. Challenges include uncertainties in sensitivity for specific AVM features. Detecting AVMs in challenging locations, such as the apical cranial convexity, is further complicated, demanding careful consideration due to the risk of underestimating total blood flow. Navigating these challenges, ASL provides a noninvasive avenue with undeniable merits, but a balanced approach considering its limitations is crucial. Larger-scale prospective studies are needed to comprehensively evaluate the diagnostic performance of ASL in AVM assessment.

Real-Time MRI Monitoring of Liquid Embolic Agent (Onyx) Injection in a Swine Arteriovenous Malformation Model

The paradigm is gradually shifting, with radiosurgery and endovascular embolization being increasingly chosen over surgical resection in the selected cases of brain arteriovenous malformations. Routinely used X-ray monitoring of liquid embolic infusion has very good spatial and temporal resolution but is not without significant drawbacks regarding poor visualization of the complex AVM angioarchitecture, especially after many embolizations in the past and therefore limiting the technical ability of the embocure-total occlusion of the feeding arteries, nidus, and draining veins. The purpose of this study was to evaluate the use of real-time MRI guidance in endovascular embolization with Onyx (instead of X-ray) in a single swine rete mirabile (RM) AVM model in order to provide the scaffolding for the real-time MRI guidance method. Onyx propagation was observed in real-time dynamic GE-EPI scan with initial ipsilateral RM filling followed by main cerebral arterial branch distribution. The relatively bright signal within RM and the brain prior to Onyx injection provided a good background for the dark, low signal of the embolic agent spreading in rete mirabile and brain arteries. X-ray picture confirmed Onyx cast distribution at the end of the procedure. In this initial experience, real-time MRI seems to be a promising method that may significantly improve liquid embolic agent infusion monitoring in the future, although requiring further development before clinical use.

Brain arteriovenous malformations of the middle cerebral artery region: image characteristics and endovascular treatment based on a new classification system

BACKGROUND

To date, few studies have investigated the use of endovascular treatment (EVT) for brain arteriovenous malformations (BAVMs) in the supplying area of the middle cerebral artery (MCA). Moreover, no suitable classification was aimed at EVT for MCA-BAVMs. Therefore, this study proposed a new classification.

METHODS

This study retrospectively collected 135 MCA‑BAVMs. They were classified into four types: Type I BAVMs located above the M1 segment; Type II BAVMs located in the region around the Sylvian fissure; and Type III BAVMs located in the supplying region of the M4 segment and subdivided into types IIIa and IIIb. The relevance of various types of MCA-BAVMs and their imaging characteristics and EVT outcomes was analyzed by ordinary one-way ANOVA, Tukey's multiple comparisons test and the chi-square test.

RESULTS

The 135 patients averaged 33.8 ± 14.7 years and included 75 females (55.6%, 75/135). Among them, 15 (11.1%, 15/135), 16 (11.9%, 16/135), 54 (40%, 54/135), and 50 (37%, 50/135) MCA-BAVMs were type I, II, IIIa and IIIb, respectively. After EVT, a good outcome was achieved in 97% of patients. Statistical analysis showed that type I BAVMs were smaller than type II and IIIb BAVMs (P value < 0.05), and type IIIb BAVMs were larger than type I and IIIa BAVMs (P value < 0.05). Deep vein involvement in type I and IIIb BAVMs was more common than in other types (P value < 0.05), and intraventricular hemorrhage (IVH) was also more common (P value < 0.05). The normal morphology in type IIIb was less than that in the other types (P value < 0.05). Type IIIa BAVMs had a higher degree than other types (P value < 0.05).

CONCLUSION

The present study demonstrated that the new classification of MCA-BAVMs can be used to evaluate imaging characteristics and EVT outcomes in different types. In addition, EVT may be a safe treatment modality for MCA‑BAVMs.

[Stereotactic radiotherapy of non-tumoral brain pathologies: Arteriovenous malformations and trigeminal neuralgias]

Stereotactic radiotherapy and radiosurgery allow delivery of high irradiation doses in a limited volume. These techniques are specially adapted to brain and nervous pathologies. Indication are not only cancers and tumors but also non tumor tissues such as arteriovenous malformations. In some case purpose of stereotactic radiotherapy is solely functional, for example for trigeminal neuralgia. We detail the questions that raise treatment of these non-tumor pathologies. These pathologies imply a multidisciplinary approach that associate radiation oncologists, neuro-radiologist and neurosurgeons.

Low-dose contrast-enhanced time-resolved angiography with stochastic trajectories with iterative reconstruction (IT-TWIST-MRA) in brain arteriovenous shunt

OBJECTIVES

To assess the feasibility of low-dose contrast-enhanced four-dimensional (4D) time-resolved angiography with stochastic trajectories (TWIST) with iterative reconstruction (hereafter IT-TWIST-MRA) covering the whole brain and to compare IT-TWIST-MRA and TWIST-MRA with reference to digital subtraction angiography (DSA) in the evaluation of arteriovenous shunts (AVS).

METHODS

Institutional Review Board approval was obtained for this observational study, and the requirement for written informed consent was waived. Twenty-nine patients with known AVS underwent TWIST-MRA on a 3-T MRI scanner, using low-dose injection (0.02 mmol/kg) of gadolinium-based contrast agent (GBCA) with each of Fourier and iterative reconstruction between September 2016 and October 2019. Visual evaluation of image quality was conducted for delineation of (a) the normal cerebral arteries and veins and (b) AVS feeder, shunt, and drainer vessels. Region-of-interest evaluation was conducted to evaluate bolus sharpness and baseline signal fluctuation in the signal intensity of the cerebral vessels. We compared the detection of AVS between TWIST-MRA and IT-TWIST-MRA. The paired-samples Wilcoxon test was used to test the differences between TWIST-MRA and IT-TWIST-MRA.

RESULTS

Visualization scores for normal vasculature and AVS angioarchitecture were significantly better for images produced using IT-TWIST-MRA than those using TWIST-MRA. Peak signal and the enhancement slope of the time-intensity curve were significantly higher for IT-TWIST-MRA than for TWIST-MRA, except for the superior sagittal sinus (SSS). Baseline intensity fluctuation was significantly lower for IT-TWIST-MRA than for TWIST, except for SSS.

CONCLUSIONS

IT-TWIST-MRA yields clinically feasible 4D MR-DSA images and delineates AVS even with low-dose GBCA.

KEY POINTS

• Iterative reconstruction significantly improves the image quality of TWIST-MRA covering the whole brain. • The short temporal footprint and denoising effect of iterative reconstruction enhances the quality of 4D-MRA. • IT-TWIST-MRA yields clinically feasible images of AVS with low-dose GBCA.