Spinal cord arteriovenous shunts: from imaging to management

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Abstract

Spinal cord arteriovenous shunts (SCAVSs) are either fistulas or niduses that can be separated in four different groups according to their localization and relationship to the dura. Paraspinal AVSs are located outside the spine and are responsible for neurological symptoms because of cord compression by ertatic veins, venous congestion or arterial steal. Epidural shunts are located in the epidural space and drain in epidural veins with secondary intradural congestion. Dural shunts are embedded in the dura, produce a cord venous myelopathy after draining through veins that either pierce the dura far from a nerve root or accompany a nerve root. Intradural shunts affect the cord, the roots or the filum. Additionally, they can be classified according to their potential relationships with genetics, vascular biological features and angiogenesis into genetic hereditary lesions (hereditary hemorrhagic telangiectasia), genetic non-hereditary lesions (multiple lesions with metameric links) and single lesions (AVMs or micro AVFs). MRI and MRA are able to visualise SCAVS early after the onset of clinical symptoms. The type of shunt and its localization may remain difficult to be precise. Angiography remains the gold standard for analysis of the anatomical, morphological and architectural features necessary for therapeutic decisions in both paediatric and adult populations. In our series, embolisation is chosen in first intention whatever the type of shunt responsible for the clinical symptoms and glue is preferably used. In paraspinal, dural or epidural arteriovenous shunts, the goal of treatment should be complete closure of the shunt. A complete cure by embolization is rather easily achieved in paraspinal lesions. Failure of endovascular therapy in dural or epidural shunts must bring the patient to surgery. The prognosis of most intradural shunts seems better than previously thought, even after haemorrhage. In intradural spinal cord arteriovenous shunts, embolisation targeted towards the portions of the malformation felt to be responsible for the symptoms (venous congestion) or pointing to the point of rupture (false aneurysms) of the malformation, allows restoration of a new hemodynamic equilibrium between the malformation and the cord itself. Such targeted treatment offers long-term stabilisation or improvement to patients suffering from SCAVSs and good protection against (re) haemorrhages, with an acceptable morbidity. Cure of the shunt is not imperative to obtain these satisfactory outcomes. The clinical results obtained by such management compare favourably with those obtained by neurosurgery.

Introduction

Spinal cord arteriovenous shunts (SCAVSs) are rare lesions that represent about only one-tenth of brain arteriovenous shunts [1]. They are considered devastating lesions: with a poor prognosis when discovered and with poor outcome if revealed by haemorrhage [2], [3], [4], [5]. They have given rise to a large literature, dealing with different analyses that have oriented patients towards various treatment modalities that range from surgery [1], [4], [6], [7], [8], [9], [10], [11], [12], embolisation [3], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26] or a combination of both [13], [29], [30], [31], [32]. The results of these different treatments are variable and often not available for long-term follow up studies.

The purpose of this paper is to report our experience with treatment of SCAVSs and to propose guidelines for management of these lesions.

Section snippets

Classification of spinal cord arteriovenous shunts

Several classifications have been proposed [5], [13], [20], [33], [34], [35], [36], [37]. They divide SCAVSs into subgroups on the basis of morphological data, thus creating a glossary, supposed to facilitate the understanding of the shunts, on which appropriate treatments according to the types of vascular malformations can be based. These classifications, however, show differences that may create unfortunate confusion, mainly due to the subjective interpretation of angiographic data or

Localisation with regard to the spinal cord

SCAVSs can be analyzed according to their position to the dura, which represents a landmark.

These lesions are located outside the spinal cord and the spine.

Arteriovenous fistulas

These fistulas represent direct communications between arteries and veins without interposition of any pathological network. They are always superficial [3], [34]. Fistulas can be subdivided into two groups [38]: Micro arterio-venous fistulas (micro AVFs): small size lesions fed by one or multiple arteries of different calibre and draining into moderately enlarged veins; Macro arterio-venous fistulas (macro AVFs) are high-flow shunts fed by large arteries and draining directly into a giant

Potential relationships with genetics, vascular biological features and angiogenesis

We have proposed a reappraisal of the classification of intradural SCAVSs that takes into account the supposed origin of each shunt and its relationship to a possible underlying disease [38]. Assessment of the angioarchitecture, which is supposed to reflect the evolving potential of intradural SCAVSs, will also be part of this pre-therapeutic analysis. Both descriptions emphasise the concept of ‘host’ and the equilibrium that exists between the lesion and the cord itself.

Our classification

Pathophysiology of symptoms of spinal cord AVS. Natural history. Relationship with angioarchitecture

Arterial steal and cord ischemia of arterial origin has never been proven in our experience of intradural, dural or extradural shunts, although it has been advocated to explain progressive impairment occurring at long term follow up in patients with SCAVSs [56].

Veins represent the key factor in the onset of neurological symptoms in any type of SCAVS [3], [26].

Neuroradiology of spinal cord arteriovenous shunts

SCAVSs are characterised by their draining veins. These are well depicted on MRI and the vascular origin of the symptoms can therefore be made early. It might however be difficult, or impossible, to precise the shunt involved (type and localization). Angiography therefore remains the gold standard for diagnosis, analysis and description of SCAVSs. The MRI appearance of an associated haemorrhage, whatever its type, will be identical to any other bleed.

In paraspinal arteriovenous shunts, T1 or T2

Therapeutic management of spinal arteriovenous shunts

Embolisation is performed in first intention in most of the cases of our series, whatever the type of lesion. The therapeutic strategy has remained the same over 25 years since the beginning of Bicetre's experience. Cure of the shunt with a stable material is a mandatory goal to be reached in paraspinal, dural or epidural lesions in order to avoid further clinical deterioration [3], [26]. However, partial, targeted endovascular therapy stabilises the evolution of intradural SCAVSs at long-term

Conclusions

MRI has improved the diagnosis of spinal cord arteriovenous shunts. At present, as soon as neurological symptoms suggesting a vascular origin appear, an early diagnosis of a SCAVS can be made. The type of shunt and its localization may however still remain difficult to precise by MRI and MRA. Angiography remains the gold standard for optimal analysis of the anatomical, morphological and angio-architectural features necessary for therapeutic decisions in both the paediatric and adult

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