Staging of arteriovenous malformations using three-dimensional time-of-flight MR angiography and volume-rendered displays of surface anatomy

Presurgical Planning with Open-Source Horos Software for Superficial Brain Arteriovenous Malformations

BACKGROUND

Surgical planning for treating brain arteriovenous malformations (bAVMs) is challenging because it entails visualizing 3-dimensional (3D) relationships between the nidus, its feeding and en passage arteries, and draining veins. Surgical experience in developing the capacity to mentally visualize pathological bAVM angioarchitecture could be complemented by this software, and thus potentially lower the steep learning curve for understanding complex bAVM angioarchitecture. We evaluated the clinical application of freely available online 3D reconstruction software in facilitating visualization of AVM angioarchitecture for presurgical planning.

METHODS

Preoperative Digital Imaging and Communications in Medicine magnetic resonance imaging/magnetic resonance angiography images of 56 superficial bAVMs from 2013 to 2018 were processed using open-source software Horos. 3D rendered images were compared with the surgical view to evaluate software accuracy and determine its value as a preoperative tool. 3D reconstructed images were compared with intraoperative recordings.

RESULTS

A useful image identifying both the main feeding artery and draining vein was achieved in 35 of 56 cases (62.5%). Reconstructions of small AVMs (nidus ≤2 cm) and those located within the temporal or cerebellar cortex were less useful due to soft tissue artifacts. Frontal and parietal lobe lesions had significantly higher rates of identifying feeding arteries and draining veins (P < 0.05).

CONCLUSION

Presurgical planning for resection of superficial bAVMs using Horos software allows for a comprehensive 3D analysis of the bAVM angioarchitecture. This technique is most useful for frontal and parietal lobe lesions, and aids the surgeon in formulating an optimal surgical strategy. The 3D reconstruction of the brain surface offers a surgical map not influenced by brain shift.

Multimodale MR-Diagnostik arteriovenöser Malformationen

Arteriovenous malformations (AVM) are complex inborn malformations of the vascular system. In the brain they can lead to severe complications, such as parenchymal haemorrhaging, epileptic seizures or neurologic failure, which necessitates a safe diagnosis and therapy. In addition to conventional angiography, magnetic resonance imaging (MRI) and MR angiography (MRA) have now been established as the gold standard diagnostic procedures. Using MRA the angioarchitecture of malformations can be captured and with a parallel imaging of the parenchyme the method is very well suited for therapy planning and monitoring. This review summarizes the present day possibilities of multimodal MRT diagnosis of AVM and describes the purely morphologic as well as the physiologic and pathophysiologic characteristics. The various MR angiographic techniques will be firstly described with respect to the basic technical principles and the results obtained so far will be summarized. The principle of functional MRT will be described and the diagnostic possibilities with respect to AVM will be discussed.

Non-invasive assessment of vessel morphology and function in tumors by magnetic resonance imaging

The switch to an angiogenic phenotype is an important precondition for tumor growth, invasion and spread. Since newly formed vessels are characterized by structural, functional and molecular abnormalities, they offer promising targets for tumor diagnosis and therapy. Previous studies indicate that MRI is valuable to assess vessel morphology and function. It can be used to distinguish between benign and malignant lesions and to improve delineation of proliferating areas within heterogeneous tumors. In addition, tracer kinetic analysis of contrast-enhanced image series allows the estimation of well-defined physiological parameters such as blood volume, blood flow and vessel permeability. Frequently, changes of these parameters during cytostatic, anti-angiogenic and radiation therapy precede tumor volume reduction. Moreover, target-specific MRI techniques can be used to elucidate the expression of angiogenic markers at the molecular level. This review summarizes strategies for non-invasive characterization of tumor vascularization by functional and molecular MRI, hereby introducing representative preclinical and clinical applications.

High-resolution MR venography of cerebral arteriovenous malformations

The purpose of this study was to evaluate the diagnostic potential of a high-resolution magnetic resonance (MR) venography technique in patients with cerebral arteriovenous malformations (AVMs). A high-resolution 3D gradient echo sequence was used with a long echo time TE to obtain venous information down to sub-pixel sized vessel diameters of several hundred microns. The method is based on the paramagnetic property of deoxyhemoglobin, and the resulting developing phase difference between veins and brain parenchyma at long echo times which leads to signal cancellation. The reconstructed venograms were compared with time-of-flight (TOF)-MR angiography using qualitative and quantitative criteria with the conventional digital subtraction angiography serving as the reference gold standard. In 17 patients with angiographically proven cerebral AVMs, the method indicates its potential in clinical applications. Venography was able to detect all AVMs whereas TOF-MRA failed in three patients. In the delineation of venous drainage patterns MR venography was superior to TOF-MRA, however, the method failed in the detection of about half of the main feeding arteries, as expected. Due to susceptibility artifacts at air/tissue boundaries and interference with paramagnetic hemosiderin, venography was limited with respect to the delineation of the exact nidus sizes and shapes in ten patients with AVMs located close to the skull base or having suffered from previous bleeding. Although the visualization of draining veins represents an important prerequisite in the surgical and radiosurgical treatment planning of cerebral AVMs, application of high resolution MR venography may be limited in the diagnostic work-up in some of these patients. On the other hand, it may be of special importance in the early detection and assessment of small AVMs that are difficult to diagnose with other MR methods.

Initial experience with helical CT and 3D reconstruction in therapeutic planning of cerebral AVMs: comparison with 3D time-of-flight MRA and digital subtraction angiography

PURPOSE

We report our initial experience with helical CT and CT angiography (CTA) in evaluating cerebral arteriovenous malformations (AVMs) in comparison with time-of-flight MR angiography (MRA) and digital subtraction angiography (DSA).

METHOD

Twelve AVMs were studied with CTA, non-gadolinium-enhanced MRA, and DSA. Reconstructed images were obtained in three display methods (maximum intensity projection, shaded surface black and white, shaded surface color). Shaded surface color display was obtained by assigning different colors to vessels and "presumed" nidus. The number of feeding arteries and draining veins associated with each AVM was independently counted in each modality. The relative ease of depicting the nidus and vessels was also determined in each display method. AVM nidus dimensions were measured on CTA and MRA source images and interobserver differences were compared.

RESULTS

CTA-reconstructed images depicted more veins but fewer arteries than MRA. Shaded-surface color displays best delineated vessels and nidus. Nidus dimension measurement was possible on CTA in all AVMs but impossible on MRA in four AVMs due to interference by methemoglobin (three AVMs) and phase artifact (one AVM). The interobserver difference in nidus dimension as measured on CTA was significantly smaller than that on MRA.

CONCLUSION

Reconstructed CTA images and CTA source images seem to be valuable adjuncts or alternatives to MRA.