Detection of residual brain arteriovenous malformations after radiosurgery: diagnostic accuracy of contrast-enhanced four-dimensional MR angiography at 3.0 T

Objective

To evaluate the diagnostic accuracy of four-dimensional MR angiography (4D-MRA) at 3.0 T for detecting residual arteriovenous malformations (AVMs) after Gamma Knife® (Elekta Instrument AB, Stockholm, Sweden) radiosurgery (GKRS).

Methods

We assessed 36 angiographically confirmed AVMs in 36 patients who had been treated with GKRS. 4D-MRA was performed after GKRS and the time intervals were 39.4±26.0 months [mean±standard deviation (SD)]. 4D-MRA was obtained at 3.0 T after contrast injection, with a measured voxel size of 1×1×1 mm and a temporal resolution of 1.1 s (13 patients) or a voxel size of 1×1×2 mm and a temporal resolution of 0.98 s (23 patients). X-ray angiography was performed as the standard reference within 53±47 days (mean±SD) after MRA. To determine a residual AVM, the 4D-MRA results were independently reviewed by two readers blinded to the X-ray angiography results. We evaluated diagnostic sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of 4D-MRA for detection of a residual AVM.

Results

A residual AVM was identified in 13 patients (13/36, 36%) on X-ray angiography. According to Readers 1 and 2, 4D-MRA had a sensitivity of 79.6% and 64.3%, a specificity of 90.9% and 100%, a PPV of 84.6% and 100% and an NPV of 90% and 81.5%, respectively, and a diagnostic accuracy of 86.1% for Readers 1 and 2, for detecting residual AVMs after GKRS.

Conclusion

The diagnostic accuracy of 4D-MRA at 3.0 T seems high, but there is still the possibility of further improving the spatiotemporal resolution of this technique.Arteriovenous malformations (AVMs) of the brain are congenital vascular anomalies consisting of a complex web of feeding arteries and draining veins, linked by an abnormal capillary bed—the so-called nidus. Although they can remain silent over a long period of time, because of their possible long-term morbidity or life-long risk of bleeding (approximately 2–4% per year), brain AVMs are usually treated by surgical resection, by complete obliteration by either endovascular embolisation or Gamma Knife® (Elekta Instrument AB, Stockholm, Sweden) radiosurgery (GKRS) or by a combination of all three [1-3].GKRS is increasingly used for the treatment of small or residual AVMs after surgical resection or embolisation. After GKRS, the microvascular structures within the AVM begin to be obliterated by the endothelial cell damage and proliferation of smooth muscle cells, which usually continues for 2–3 years [4]. Because the risk of bleeding persists as long as complete obliteration is not obtained, most physicians usually follow up patients at a regular interval to evaluate the response to GKRS. X-ray angiography is a gold standard for post-therapeutic monitoring of AVMs. However, it is an invasive procedure, and its potential neurological complications, ranging in incidence from 0% to 12.2%, hinder its use as a routine follow-up study [5,6]. Consequently, several non-invasive MRI and MR angiography (MRA) techniques have been proposed as a non-invasive alternative to X-ray angiography to assess the response of AVMs and adjacent brain parenchyma.Time-of-flight (TOF) MRA is a commonly used MRA technique for the assessment of residual AVMs after GKRS. However, TOF MRA produces only static images of AVMs and lacks haemodynamic information. Another non-invasive technique, contrast-enhanced four-dimensional MRA (4D-MRA), is an emerging new technique without these limitations and demonstrates a good correlation with X-ray angiography with respect to the Spetzler–Martin classification on initial assessment of AVMs prior to treatment [7-13]. However, the diagnostic accuracy of 4D-MRA for the detection of residual AVMs after GKRS is not well known. Only Gauvrit et al [14] reported that the sensitivity and specificity for the detection of residual AVMs after GKRS were 81% and 100%, respectively. But their study was performed using a 1.5 T MRI system.Therefore, the purpose of this study was to evaluate the diagnostic performance of 4D-MRA for detecting residual AVMs after GKRS at 3.0 T, compared with X-ray angiography.     

Stereotactic neutron radiosurgery for arteriovenous malformations of the brain

A technique employing single fraction neutron radiosurgery for treatment of intracranial vascular malformations has been developed at the University of Washington and is described in this report. The natural history of arteriovenous malformations of the brain is briefly reviewed, along with currently available therapeutic methods for treatment of these lesions. The characteristics of the neutron beam used for radiosurgery are described, along with methods for patient immobilization, radiation treatment planning, dosimetry, and delivery of treatment using this technique.     

Stereotactic radiosurgery of arteriovenous malformations

Stereotaxis has been introduced at the Joint Center for Radiation Therapy in Boston, MA, to aid in the precise localization and treatment of arteriovenous malformations (AVMs). A Brown-Roberts-Wells stereotactic system and a 6 MV linear accelerator have been modified for these treatments. By using multiple isocentric rotational fields, radiation doses from 1500 to 2500 cGy can be safely prescribed to the AVM in efforts to occlude the blood vessels without risking damage to nearby radiosensitive structures. Sixteen patients have been treated from February 1986 to July 1988 using the technique described.     

Results of neutron radiosurgery for inoperable arteriovenous malformations of the brain

Twenty patients with inoperable arteriovenous malformations (AVMs) of the brain were treated with neutron radiosurgery. A 50 MeV cyclotron was used to deliver 9 Gy in a single fraction through 7 to 14 isocentric portals. The size and shape of the portals were customized to each treatment site. Nineteen patients have been followed for a median duration of 24 months following neutron radiosurgery. A radiographically demonstrable partial response was seen in 8 patients (42%). No complete responses were observed. There has been one post-treatment hemorrhage, no fatalities, and no evidence of radiation toxicity. The low response rate and absence of toxicity suggest that the appropriate dose for neutron radiosurgical treatment of AVMs is higher than the dose of 9 Gy at isocenter used in this initial study.     

Confounding effect of large vessels on MR perfusion images analyzed with independent component analysis

BACKGROUND AND PURPOSE: First pass contrast-enhanced MR imaging using gradient-echo acquisitions is commonly used to assess cerebral blood flow, despite the confounding signal from large blood vessels. We hypothesized that removal of this unwanted intravascular signal using independent component analysis would result in a more accurate depiction of cerebral blood flow. METHODS: Images of 11 patients, acquired with our acute stroke imaging protocol, were post processed to produce images of relative cerebral blood flow (rCBF). The same images were processed with independent component analysis to identify and remove the signal from large blood vessels, with a second set of rCBF images produced. Both sets of rCBF maps were pooled, randomized in order, and read in a blinded fashion by two neuroradiologists to assess the level of large artery artifact and overall image quality. Significance was determined using a Wilcoxon signed rank test. RESULTS: Results from both readers indicated that the level of large artery artifact was significantly reduced in the images processed using independent component analysis component removal (P <.05). In addition, both readers indicated significantly (P <.05) improved image quality of the images processed using independent component analysis. CONCLUSION: The removal of the signal resulting from large blood vessels before calculation of rCBF resulted in images with significantly less artifact and higher image quality.     

Revascularization of brain arteriovenous malformations after embolization with brucrylate

Summary Between 1984 and 1988, 52 brain arteriovenous malformations (AVMs) were embolized in the Radiology Department of the Toronto Western Hospital. 9 were localized in the occipital lobe. There was angiographic follow-up ranging from one to four years. Two embolized AVMs, both occipital, showed revascularisation at 6 months and two years respectively. In one case the embolization had resulted in a complete obliteration of the AVM. In the other, the nidus was reduced by 95%. It is suggested that the occipital lobe, because of its rich vascularity, is more prone than other parts of the brain to produce intense collateralization leading indirectly to resupply of embolized AVMs. Existence of these collaterals may also explain the rarity of visual defects in occipital AVMs. These cases confirm the need for post therapeutic angiographic controls to assess the stability of the results obtained.     

Treatment of arteriovenous malformations of the brain with combined embolization and stereotactic radiosurgery: results after 1 and 2 years

Seven patients with large arteriovenous malformations (AVMs) of the brain were selected for combined therapy with particulate embolization, followed by radiosurgery of the residual nidus. The goal of embolization was to reduce the patient nidus to a size that facilitated successful stereotactic radiosurgery. Angiograms obtained 1 and 2 years after radiosurgery were evaluated for changes in nidus size, flow rate, and feeding and draining vessels. One year after stereotactic radiosurgery, one AVM was angiographically undetectable. Three other AVMs demonstrated a volume reduction of greater than 50%, in addition to decreased shunt speed and altered angioarchitecture at 1-year follow-up. At 2-year follow-ups, two of seven AVMs were cured, and an additional two of seven had a greater than 98% reduction in nidus volume. Although one patient experienced a transient deficit from embolotherapy, none of our patients suffered a new neurologic deficit or a hemorrhage during the follow-up period. Our data support the efficacy of combined embolotherapy and radiosurgery for definitive therapy of selected large AVMs of the brain.     

Hemodynamic segmentation of MR brain perfusion images using independent component analysis, thresholding, and Bayesian estimation.

Dynamic-susceptibility-contrast MR perfusion imaging is a widely used imaging tool for in vivo study of cerebral blood perfusion. However, visualization of different hemodynamic compartments is less investigated. In this work, independent component analysis, thresholding, and Bayesian estimation were used to concurrently segment different tissues, i.e., artery, gray matter, white matter, vein and sinus, choroid plexus, and cerebral spinal fluid, with corresponding signal-time curves on perfusion images of five normal volunteers. Based on the spatiotemporal hemodynamics, sequential passages and microcirculation of contrast-agent particles in these tissues were decomposed and analyzed. Late and multiphasic perfusion, indicating the presence of contrast agents, was observed in the choroid plexus and the cerebral spinal fluid. An arterial input function was modeled using the concentration-time curve of the arterial area on the same slice, rather than remote slices, for the deconvolution calculation of relative cerebral blood flow.     

Hemodynamic segmentation of MR perfusion images in patients with unilateral carotid stenosis using independent component analysis

Purpose

To assess spatiotemporal patterns of local perfusion in MR brain perfusion images for patients with unilateral carotid stenosis.

Materials and Methods

MR perfusion images acquired from 12 patients with unilateral carotid stenosis were retrospectively segmented using independent component analysis. Regions of interest selected from the segmentation results were used to measure the time to peak (TTP), time to maximum of the residue curve (T_max), and mean transit time (MTT) for arteries and brain parenchyma on normal and stenotic sides.

Results

The tissue types that can be identified in segmentation results include normal artery, artery with proximal stenosis, normal brain parenchyma, delayed‐perfusion brain parenchyma, vein and sinus, choroid plexus, cerebrospinal fluid, and leukoaraiosis. Concentration–time curves measured on normal and stenotic artery regions can be modeled as two arterial input functions. Unilateral carotid stenosis associated with either middle cerebral artery stenosis or poor collateral circulation at the circle of Willis resulted in increased differences of brain parenchyma TTP, T_max, and MTT between normal and stenotic sides.

Conclusion

Independent component analysis on perfusion images of patients with unilateral carotid stenosis provides useful spatiotemporal information regarding blood supply to arteries and local perfusion of brain parenchyma. J. Magn. Reson. Imaging 2008;28:1125–1132. © 2008 Wiley‐Liss, Inc.     

Contrast-enhanced MR perfusion imaging and MR angiography: utility for management of pulmonary arteriovenous malformations for embolotherapy

Objective: The purpose of this study was to assess the capability of MR perfusion imaging and angiography (MRA) for management of pulmonary arteriovenous malformation (PAVM). Methods and patients: Eight patients, having 15 PAVMs underwent pulmonary angiography (PAG), CT, MR perfusion imaging and MRA. For the pretherapeutic management, MRA was compared with PAG and CT regarding detectability and diameter of vasculature. For post-therapeutic management, the change in size of aneurysmal sac, any residual contrast-enhancement and the blood supply within the sac were evaluated. Results: All PAVMs with aneurysmal sac, feeding artery and draining vein diameters of equal to or more than 3 mm, were identified and measured with similar results by all modalities. On follow-up studies, 7 (58.4%) out of 12 treated PAVMs showed a decrease in size and residual contrast-enhancement. The residual contrast-enhancement was considered as bronchial artery-to-pulmonary artery collateral flow by MR perfusion imaging. Conclusion: MR perfusion imaging and MRangiography are useful for management of PAVMs over 3 mm in diameter.     

Late clinical and radiological complications of stereotactical radiosurgery of arteriovenous malformations of the brain

Introduction

Post-radiation injury of patients with brain arteriovenous malformations (AVM) include blood–brain barrier breakdown (BBBB), edema, and necrosis. Prevalence, clinical relevance, and response to treatment are poorly known. We present a series of consecutive brain AVM treated with stereotactic radiosurgery describing the appearance of radiation injury and clinical complications.

Methods

Consecutive patients with annual clinical and radiological follow-up (median length 63 months). Edema and BBBB were classified in four groups (minimal, perilesional, moderate, or severe), and noted together with necrosis. Clinical symptoms of interest were intracranial hypertension, new neurological deficits, new seizures, and brain hemorrhages.

Results

One hundred two cases, median age 34 years, 52 % male. Median irradiated volume 3.8 cc, dose to the margin of the nidus 18.5 Gy. Nineteen patients underwent a second radiosurgery. Only 42.2 % patients remained free from radiation injury. Edema was found in 43.1 %, blood–brain barrier breakdown in 20.6 %, necrosis in 6.9 %. Major injury (moderate or severe edema, moderate or severe BBBB, or necrosis) was found in 20 of 102 patients (19.6 %). AVM diameter >3 cm and second radiosurgery were independent predictors. Time to the worst imaging was 60 months. Patients with major radiation injury had a hazard ratio for appearance of focal deficits of 7.042 (p?=?0.04), of intracranial hypertension 2.857 (p?=?0.025), hemorrhage into occluded nidus 9.009 (p?=?0.079), appearance of new seizures not significant.

Conclusions

Major radiation injury is frequent and increases the risk of neurological complications. Its late appearance implies that current follow-up protocols need to be extended in time.     

Linear accelerator-based radiosurgery for multiple arteriovenous malformations: case report

This report presents a rare case of multiple, widely spaced arteriovenous malformations in a single patient treated with linear accelerator-based radiosurgery. The choices associated with the requisite imaging and planning are presented. In light of the anatomic topography, linear accelerator-based radiosurgery was chosen over gamma knife treatment, with CT angiography being used to image all target areas simultaneously.     

Management of patients with brain arteriovenous malformations

Arteriovenous malformations (AVMs) of the brain, which are probably genetically determined, are errors in the development of the vasculature that, together with the effects of blood flow, may lead to a focal arteriovenous shunt. Clinically, the adult patient may present with acute or chronic neurological symptoms-fixed or unstable-such as deficits, seizures or headache. Sometimes the lesion is an incidental finding. In about half of the patients, the revealing event is an intracranial haemorrhage. The prevalence of AVM in the western world is probably <0.01% and the detection rate is about one per 100,000 person-years. Most AVMs are revealed in patients 20-40 years of age. Therefore, the risk of developing neurological symptoms from an AVM, usually because of haemorrhage, increases with patient age. In the young adult population, AVMs are significant risk factors for hemorrhagic stroke. This risk increases with AVM volume and is higher in centrally located AVMs. Almost all patients with AVM are subjected to treatment, either by surgery, radiosurgery or embolisation, with the functional aim of reducing the risk of haemorrhage or to alleviate neurological symptoms with an acceptable treatment risk. Few neurocentres have physicians highly skilled in all treatment modalities. Therefore, the prescribed treatment may not be defined from an objective assessment of what is optimal for each individual patient, but rather from local expertise. In this context, more and better data about the natural history and the outcome of different treatments, as well as predictive models, would be valuable to help to optimise the management. Management strategies obviously differ according to local preferences, but results presented in the literature suggest the following strategy: (I) cortically located AVMs with a nidus volume <10 ml could be operated, with or without presurgical embolisation, unless there is a single feeder that can easily be catheterised and embolised for obliteration or other obvious target for embolisation, such as pseudoaneurysms or large fistulae; (II) centrally located AVMs with a nidus volume <10 ml should be treated by radiosurgery, unless suitable for embolisation as indicated above; (III) patients harbouring AVMs with a nidus volume >10 ml could benefit from targeted partial embolisation followed by radiosurgery or surgery, depending on the angioarchitecture; and (IV) AVMs >20 ml nidus volume usually have a high treatment risk with any treatment modality and are not obvious targets for treatment at all.     

MR imaging of dural arteriovenous malformations with ocular signs

Summary Four patients with dural arteriovenous malformation (AVMs) draining into the cavernous sinus, who presented ophthalmic manifestations, were studied by magnetic resonance (MR) imaging. In all patients signal decrease in the involved cavernous sinus was demonstrated in coronal spinecho (SE) imaging. It is attributable to rapid venous flow in the sinus, and this high velocity signal loss is a fairly pathognomonic finding in this condition. We stress the validity of MR imaging in the primary diagnosis of dural AVMs with ophthalmic symptoms.     

Intracerebral arteriovenous malformations: evaluation with selective MR angiography and venography

Magnetic resonance (MR) angiography and spin-echo methods were used to evaluate intracerebral arteriovenous malformations (AVMs) in 10 patients. Spin-echo images obtained with flow presaturation demonstrated the nidus of the AVM in all cases, but it was difficult to determine feeding vessels. These vessels were directly visualized with three-dimensional MR angiography; their presence could be indirectly determined by means of selective presaturation of individual vessels, which resulted in a marked decrease in signal within the portion of the AVM supplied by that vessel. Vascular supplies from the internal carotid artery and anterior, middle, or posterior cerebral arteries were detected in all cases, but in three large malformations it was not possible to demonstrate small feeding vessels. MR angiograms were also helpful for further defining the nidus. The combination of MR angiographic and spin-echo methods provides information useful for therapeutic planning not provided by either technique alone.