Intrinsic Spinal Cord Arteriovenous Malformations

Spinal cord arteriovenous shunts (SCAVSs) represent a complex group of lesions, often feared because often misunderstood. The fear is created by the eloquence of the cord, by the poor reputation that SCAVSs carry, because the vascular anatomy of the cord is poorly interpreted and thus still considered difficult. The rarity of the disease doesn’t allow physicians to be confronted often to these lesions. A “rare disease” is a condition that affects a restricted number of persons with regard to the general population. The tolerated threshold for a rare disease in Europe is thus on 1 person on 2000. In France one admits that a disease is rare if less than 30 000 patients are affected. If we consider that definition, SCAVSs do certainly belong to that category. From a morphological point of view, SCAVSs can be separated in two groups: nidus-type arteriovenous malformations (AVMs) (that can be either intramedullary embedded in the cord, or superficial) and arteriovenous fistulas (AVFs) (always superficial to the cord, either being micro fistulas (mAVFs) or macrofistulas (MAVFs) characterized by giant venous ectasias). SCAVSs described as “glomus type malformations” are sometimes simple arterio-venous fistulas that engorge focally, on a given myelomeric level, the intrinsic and extrinsic venous network, giving thus rise to a pseudo AVM. In order to properly understand these lesions, it is therefore important to analyze precisely the lesional and regional anatomies of the shunt and the surrounding vasculature. The descriptions and interpretations should also take into consideration the evolutive aspects of the shunt that are expressed in the changes and modifications of architecture over time with incidences on both morphology and symptoms, and reflected by recent data on genetics, metameric dispositions, vascular biological features, and angiogenesis (Carmeliet 2000, Gibbons and Dzau 1994, Lasjaunias et Al 2001, Mc Allister et Al 1994, Risau 1995, 1997). Looking therefore only at the gross “external” aspect of a SCAVS is indeed: – dangerous because the description may vary with physicians; – incomplete because it does not reflect that the shunt is a vascular answer to a trigger acting primarily on an endothelial cell; – erroneous because it does not take in consideration the dynamics of the lesion. Any therapeutic management should be discussed in relation with the natural history of the disease. Little is known about the behaviour of intra-dural SCAVSs in children, and even less in early childhood. If it is grossly circumscribed in adults, the natural history of intra-dural SCAVSs can hardly be extrapolated to the paediatric population. The immaturity at birth of the cerebral venous system in humans has been shown to be an important factor in the presentation of neonates and infants with intra-cranial vascular malformations. The post-natal maturation of the spinal venous system remains poorly understood. It is likely that this system undergoes minor changes after birth compared to the intra-cranial venous system, because the events that normally occur at the level of the spinal cord are the oldest ones in terms of phylogeny and they can be considered as stable programs. However, the joint maturating processes of the vasculature and spinal cord may play a role in the development of the shunt itself and in its revealing symptoms. All of these data suggest therefore that SCAVSs should be viewed differently. The recent classification that we have proposed (Rodesch 2002) takes in consideration these data and tries to present objective solutions for delineation of these lesions.