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Vascular Malformations of the Nervous System

 

 

Vascular malformations are abnormalities of the blood vessels within the nervous system. Some are present from early in the development of the foetus and some are thought to be acquired later in life. There are many different types which may be classified according to how the blood circulates through them.

Vascular malformations may remain entirely asymptomatic through life. As high quality imaging of the brain becomes more accessible they are discovered by accident with increasing frequency. It is somewhat contentious whether or not

Cavernomas
constitute a variety of vascular malformation. Cavernomas are dealt with here in more detail.

Broadly speaking there are malformations which demonstrate arteriovenous shunting and those which do not. Arteriovenous shunting occurs when blood flows directly into the venous system from the arteries without passing through a capillary bed and/or supplying tissue with oxygen and nutrients. They may also be described in terms of where they are located in the nervous system.

 

Arteriovenous Shunts

An arteriovenous shunt is present when blood passes directly into the venous system from the arteries without passing through a capillary bed and/or supplying tissue with oxygen and nutrients.:

  • Arteriovenous Malformations (AVM) are characterised by the presence of a nidus of vessels at the centre. The word nidus comes form a latin word for a nest which is an apt description for the tangle of blood vessel. These may present with brain haemorrhage, seizures, stroke or a variety of other neurological symptoms. They may also remain clinically silent

  • Cerebral arteriovenous fistulae are arterio-venous connsections developing within the intrinsic blood supply, that is to say, the blood vessels dedicated to the deliver of blood to the brain and brainstem alone
  • Dural arteriovenous fistulae are arterio-venous connections developing within the leaflets of dura which cover the central nervous system
  • Vein of Galen Malformations (VGM)/Vein of Galen aneurysmal dilations (VGAD) are very rare vascuar malformations usually presenting in the newborn. A fistula develops involving a precursor of the Vein of Galen called the Median Prosencephalic Vein. The blood flow diverted through these shunts may be enough to precipitate heart failure as the newborn heart struggles to meet this demand

 

No Arteriovenous Shunt

  • Capillary Malformations (Telangectasia)
  • Cavernous Malformations (Cavernoma)
  • Developmental Venous Anomaly (DVA)- Thought to be a normal variant and functioning as part of the normal venous system of the brain. These are seen in association with cavernomas and, if removing the cavernoma, it is important to preserve the DVA.
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Mixed Malformations

As with most things in nature there are rare entities which demonstrate characteristics of both types- mixed malformations.

 

 

Arteriovenous Malformations (AVM)

Brain AVMArteriovenous malformations (AVM for short) are complicated tangles of blood vessels which can occur in almost any living tissue. They represent one of the types of vascular malformations found in the nervous system.

When found within the central nervous system they may be associated with the development of seizures or brain haemorrhage. It is likely that many remain silent and undiscovered throughout life.

Understanding what provokes an AVM to cause symptoms continues to be a focus of much research. In recent years we have come to understand that some vascular malformations may develop under genetic influence during life but there is a great deal yet to be learned.

Normally blood, laden with oxygen, passes from arteries to tiny blood vessels called capillaries where the oxygen is delivered to the organ that needs it. The blood then leaves the organ through veins on its way back to the lungs to collect more oxygen. Capillaries are missing from an AVM and the blood flows directly from arteries to veins without supplying the intended tissue.

The tangle of vessels through which the blood flows under high pressure is called the nidus from the latin word meaning "nest." Angio-architecture is the term used to describe the structure of the AVM- the configuration of the various blood vessels making it up.

Some AVMs are large and others small. Varying numbers and sizes of arteries irrigate the nidus and various veins drain it. This variety means that the stresses on any given nidus are different and this makes it dificult to predict with confidence the risk of haemorrhage for the individual.

The additional work that contributing blood vessels do in delivering high blood flow to the nidus may result in additional stresses on the vessel wall. Signs of wear-and-tear develop such as aneurysms (blister-like dilatations) on arteries or within the nidus and from these weak points the AVM may bleed.

By using the buttons at the top of this screen you can learn more about the various different types of vascular malformation and their treatment.