Central Nervous System Vascular Malformations: A Patient's Guide

by Christopher S. Ogilvy, M.D. and Stephen B. Tatter, M.D., Ph.D.
Neurosurgical Service Massachusetts General Hospital Boston, MA 02114

INDEX

• Introduction
• Initial Diagnosis
• Classification
  • Telangectasia
  • Cavernous malformation
  • Venous malformation
  • Arteriovenous malformation (AVM)
• Glossary

Introduction

The purpose of this text is to provide patients who are diagnosed with central nervous sytem vascular malformations with some background information regarding the nature of their problem and the possible alternatives in terms of treatment. It is written in terminology that is designed to minimize medical jargon and technical terms. When possible, simple diagrams are used to help explain points. The text was written with heavy input from our patients with cerebral and spinal vascular malformations.

The intent of this text is to provide basic background information. Specific details regarding any particular patient's vascular malformation should be obtained through discussions with their physician.

The text is divided into the four major types of vascular malformations that are known to occur.

Initial Diagnosis

When a patient is first diagnosed with a cerebrovascular malformation, many questions arise. The malformation may be diagnosed after a hemorrhage or as a result of a seizure or possibly as a result of headaches. With improved techniques used to visualize the brain with newer radiographic studies, the diagnosis of an asymptomatic or minimally symptomatic lesion is increasing. Regardless of how the diagnosis is made, once it is decided that a vascular malformation is present, the next step is to ascertain the exact type of vascular malformation, which influences heavily the need for treatment and the exact details of potential treatment. There are typically four distinct types of vascular malformations which may occur throughout the central nervous system, and these will be discussed separately.

Telangectasias are usually small (0.3 to 1.0 cm) lesions composed of tiny blood vessels similar to the tiny capillaries in the brain. These vessels are separated from each other by more or less normal appearing brain tissue. These lesions are rarely symptomatic during life and are most commonly found at autopsy as an incidental finding.

Cavernous malformations are more common lesions and are being discovered with increased frequency due to the advent of MRI and CT scanning. Cavernous malformations are also called cavernous angiomas, cavernomas, or sometimes simply angiomas. These vascular malformations are well-defined lesions which may reach significant size and can at times be confused with a brain tumor. When viewed under the microscope, these vascular abnormalities are made up of fairly large blood-filled channels or "caverns". These vessels are immediately adjacent to each other and there is no recognizable intervening normal brain tissue. Cavernous angiomas are at times referred to as cryptic arteriovenous malformations or occult lesions because they do not show up on routine arteriography.

Venous Malformations or venous angiomas may well represent a variant of normal veins. These have no definite arterial input. The veins within this malformation are separated by normal brain tissue. These lesions are very common, very benign in terms of their potential for hemorrhage or causing seizures, and are best left alone.

True arteriovenous malformations (AVMs)are the most significant lesions from the clinical point of view. These are composed of masses of arteries and arterialized veins which will be described in detail below. There is brain tissue between the vessels, but it is usually abnormal and often scarred from previous tiny hemorrhages of which the patient may not have been aware or may have been represented as a bad headache.

Normally in brain tissue the blood enters through major cerebral arteries but then passes through smaller arterioles and subsequently into the capillary bed. Capillaries are tiny vessels in the brain tissue, as elsewhere in the body, that allow the blood to deliver necessary oxygen and glucose to the brain and remove the end products of brain metabolism from the brain. After passing through the capillaries, the blood enters the venous system of the brain. In the veins, blood is usually blue because the oxygen has been delivered to the tissue and therefore the oxygen content of the blood is lowered. Conversely, in arteries there is a high content of oxygen as the blood enters the brain after passing through the lungs and being replenished with oxygen; therefore arterial blood is red. (Figure 1).

In the situation where an arteriovenous malformation (AVM) exists, blood is shunted directly from the arterial system to the venous system. This has several effects. For one, the oxygen content of the blood remains high as it enters the vein and therefore when looked at directly from the time of surgical exposure, the veins are red because they still carry high oxygen content blood. In addition, there is usually a pressure drop as the blood travels from the arteries to the veins. In AVMs, the flow is high and the pressure is elevated within the veins. This elevated pressure may well contribute to hemorrhages or seizures which occur with AVMs.

AVMs can occur in many locations throughout the brain and spinal cord. Often they are only detected when they cause symptoms because of where they are in the brain. For instance, if an AVM is in the speech center causes a small seizure, the patient may have difficulty speaking or finding words. If the AVM were to hemorrhage, a more severe injury to the speech area might occur in the form of more difficulty speaking. Often after an AVM has hemorrhaged the subsequent neurologic deficit does improve over days to weeks, however this depends on exactly where the blood has occurred and the size of the hemorrhage.

Glossary

Arteriography Angiography, cerebral angiography, arteriogram. A test to visualize the blood vessels in the head. This is an invasive procedure which requires that a catheter be inserted, usually in the groin or directly into the neck vessels, and threaded into the base of the skull. The dye material is then injected which shows up on x-ray, and rapid succession x-rays are taken to get a picture of the blood vessels in the head as they fill and empty with the dye material.

MRI Magnetic resonance imaging. A technique where a large magnet is used to visualize the contents of the cranium including the brain and blood vessels. This technique is noninvasive with the exception of an intravenous catheter which might be needed to give a contrast agent to better see brain lesions.