Neuroradiology (2014) 56:195–209 DOI 10.1007/s00234-013-1307-x
An approach to the symbolic representation of brain arteriovenous malformations for management and treatment planning Piotr Orlowski & Imran Mahmud & Mudassar Kamran & Paul Summers & Alison Noble & Yiannis Ventikos & James V. Byrne
Received: 20 June 2013 / Accepted: 29 November 2013 / Published online: 22 January 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract Introduction There is currently no standardised approach to arteriovenous malformation (AVM) reporting. Existing AVM classification systems focuses on angioarchitectural features and omit haemodynamic, anatomical and topological parameters intuitively used by therapists. Methods We introduce a symbolic vocabulary to represent the state of an AVM of the brain at different stages of treatment. The vocabulary encompasses the main anatomic and haemodynamic features of interest in treatment planning and provides shorthand symbols to represent the interventions themselves in a schematic representation. Results The method was presented to 50 neuroradiologists from14 countries during a workshop and graded 7.34 ± 1.92 out of ten for its usefulness as means of standardising and facilitating communication between clinicians and allowing comparisons between AVM cases. Feedback from the survey Electronic supplementary material The online version of this article (doi:10.1007/s00234-013-1307-x) contains supplementary material, which is available to authorized users. P. Orlowski (*) : A. Noble Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Old Road Campus Research Building, Oxford OX3 7DQ, UK e-mail: [email protected]
I. Mahmud : M. Kamran : P. Summers : J. V. Byrne Nuffield Department of Surgical Sciences, University of Oxford, John Radcliffe Hospital, Oxford, UK P. Summers Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy Y. Ventikos Department of Mechanical Engineering, University College London, London, UK
was used to revise the method and improve its completeness. For an AVM test case, participants were asked to produce a conventional written report and subsequently a diagrammatic report. The two required, on average, 6.19 ± 2.05 and 5.09 ± 3.01 min, respectively. Eighteen participants said that producing the diagram changed the way they thought about the AVM test case. Conclusion Introduced into routine practice, the diagrams would represent a step towards a standardised approach to AVM reporting with consequent benefits for comparative analysis and communication as well as for identifying best treatment strategies. Keywords Arteriovenous malformations . Cerebrovascular image analysis . Embolisation . Endovascular treatment . Interventional neuroradiology
Introduction With the advent of multimodal treatments of brain arteriovenous malformations (AVMs) imaging, reports need to go beyond simply referring to the supplying arteries and veins. Reflecting different approaches to summarising the angioarchitecture [1-5], a number of AVM classification systems has emerged [6-10]. In focusing on angioarchitectural features, however, these systems generally lack haemodynamic, anatomical and topological parameters that are intuitively used by therapists when planning treatments or reporting changes as treatment progresses. A standardised method for representing the relevant features of AVMs could facilitate analysis and communication of patient-specific lesion data, simplify and reduce the time needed to record treatment outcomes and provide a basis for structured case comparisons
in order to identify the best treatment strategies. Any such strategy must, however, be able to handle the heterogeneity of AVMs, be simple to implement, cover the range of information currently required for treatment and be flexible to future advances. In its simplest form, an AVM comprises an abnormal connection between a supply artery and a draining vein through a nidus. More generally, multiple vessels and nidal sub-compartments are involved; each being a potential site of embolisation and remodelling that requires identification and description of its involvement in the AVM. Relevant associated findings, such as the presence of an aneurysm or fistula need also to be documented. As well as describing baseline components of the AVM, changes over the course of treatment need to be expressed. The conventional approach to recording and communicating information about AVMs is written patient notes accompanied by hand-drawn sketches or more recently rendered views based on angiographic imaging. Anatomical information is commonly obtained from digital subtraction angiography (DSA), particularly in the context of endovascular treatment, where pre-procedural and post-procedural scans can be performed in the treatment session. Hemodynanic information though of interest is currently generally limited to subjective assessment of dynamic angiograms. In the future, advances in imaging [11-16] and modelling techniques, such as computational fluid dynamics (CFD) , may offer ways of predicting the effects of embolisation and informing treatment planning [18, 19]. To evaluate this potential, the ongoing debate [20, 21] on the application of CFD to the treatment of aneurysms may be followed. In this paper, we introduce a universally applicable symbolic description of AVMs that yields a schematic representation of traditional angiographic features and their treatment modifications (a symbolic vocabulary). A minimal example of the schema to describe an AVM in this symbolic vocabulary is seen in Fig. 1. By extending the symbolic vocabulary with annotations and textual notes that incorporate available functional and procedural data, the range of statements expressed can be broaden. The intention is not to determine and impose which features of AVMs are to be recorded but instead to provide a language in which the various steps adopted at
Fig. 1 Schematic representation of connection of a nidal compartment with an artery and a vein
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different centres or by different clinicians during treatment can be recorded in a manner immediately understandable by any AVM specialist. To assess whether the symbolic vocabulary is suited to this vision, 50 neuroradiologists from 14 countries participating in a conference workshop  were asked to apply an initial version of the vocabulary and compare it with the practice at their institution, suggest potential changes and comment on the method. The ‘Methods’ section details the resulting vocabulary, while the ‘Results’ section illustrates its use in some example cases and summarises the feedback of the workshop participants. The example cases illustrate the use of the vocabulary to record multiple endovascular AVM treatments of two patients. In the first case (Patient 1), conventional post-processing of digital subtraction angiography (DSA) together with 3D rotational acquisitions (3D-RA) complemented by superselective microcatheter angiography was used to produce a complete description of the AVM. In the second case (Patient 2), in the absence of microcatheter angiography, the anatomic and haemodynamic connectivity features are obtained from 2D-DSA and 3D-RA data. Also illustrated is how phase contrast magnetic resonance angiography (PC-MRA) and CFD could be used to provide further information about AVM blood flow and connectivity features, respectively, and a complex fictitious case is included in Supplementary material for further illustration.
Methods For treatments and particularly embolisation involving the injection of an embolic material to reduce blood flow through the AVM, we identified the following information as required or desirable in planning. These points were used as the foundation for the vocabulary: 1. The connection of the AVM with normal brain vasculature, 2. The number, location and type of vessels supplying the nidus, 3. The location of any associated aneurysms, their type and whether they were treated,
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4. Whether an individual arterial feeder can be reached with a catheter (determined based on the vessel radius or difficulties during a previous intervention), 5. The relative flow distribution between feeders and nidal compartments, 6. Qualitative blood flow and its direction in feeders and connections between compartments, 7. The type, the location and the quantity of previously deposited embolic material including any recorded leakage in the venous system, 8. Whether any devices such as coils have been used to support embolisation and 9. Whether prior haemorrhage has occurred and its location. To consolidate the process of describing AVM data, we have established a pro forma that provides space for schematic diagrams together with textual information to summarise relevant information about the AVM. The next two sections describe the symbols as well as the image post-processing necessary for constructing diagrams, with examples of the completed pro forma provided in the results section. The symbolic vocabulary Table 1 describes the symbol vocabulary for constructing diagrams representing the anatomy of an AVM and its endovascular treatment across the range of variation seen in clinical practice. Additional information about haemodynamic features and details of the anatomy and treatment can be incorporated into the description through numerical and textual annotation fields (placement and format are described in Table 1). Globally relevant information can be recorded alongside the schema as patient or procedure metadata. Symbols introduced after analysis of feedback from the workshop survey are marked with an asterisk in brackets at the end of the symbol description in Table 1. We have adopted the convention that arteries are positioned to the left of the figure, and the veins to the right, such that the anticipated direction of blood flow is from left to right. The grammar of the descriptions is largely determined by this assumption of left to right blood flow and a stereotypical placement of annotations that allow more complete descriptions to be expressed. The symbols and annotations can be classified in six categories: (1) supply vessels, (2) nidal compartments and fistulae, (3) connections to supply vessels, (4) aneurysms, (5) special symbols and annotations and (6) AVM metadata.
additional vertical line immediately after the circle is used for an abnormal vessel. The nature of the abnormality should be reported in the comments section of the pro forma. Two arrowheads pointing towards each other are used to represent stenosis of a supply vessel. For a blocked supply vessel, a capacitor symbol is used. A line connecting the capacitor plates is used if the pedicle has been previously blocked and then recanalised. The convention that arteries are positioned to the left of the figure, and the veins to the right, such that the anticipated direction of blood flow is from left to right, was adopted. There are four annotations for arteries: 1. The vessel label, 2. Vessel diameter (d) in millimetre and also described pragmatically as small (S: d