arteriovenous malformations

Other vascular lesions that affect the central nervous system

In addition to AVMs, there are three other main types of vascular lesions that can occur in the brain or spinal cord. These lesions differ from AVMs as they involve only one type of blood vessel and do not carry the same high risk of significant hemorrhage. Generally, these low blood flow lesions tend to cause fewer troublesome neurological symptoms and require less aggressive treatment compared to AVMs.

Cavernous malformations

These lesions are formed by clusters of tightly packed, abnormally thin-walled, small blood vessels that displace normal brain or spinal cord tissue. The vessels contain slow-moving or stagnant blood, often clotted or decomposed. Cavernous malformations can vary in size, ranging from fractions of an inch to several inches, depending on the number of blood vessels involved. Some individuals may develop multiple lesions. Due to the fragility of the blood vessel walls, cavernous malformations can occasionally leak blood into surrounding tissues, potentially leading to seizures. After AVMs, cavernous malformations are the most likely type of vascular lesion to require treatment.

Capillary telangiectases

These are clusters of abnormally swollen capillaries that are typically less than an inch in diameter. They are generally benign and rarely cause extensive damage to surrounding brain or spinal cord tissues. Any bleeding that occurs is microscopic in size. However, in certain inherited disorders where individuals develop numerous telangiectases, they can contribute to the development of headaches or seizures.

Venous malformations

These lesions consist of abnormally enlarged veins. They usually do not disrupt blood vessel function and seldom cause hemorrhages. Most venous malformations do not produce noticeable symptoms and often go undetected.

Who is more likely to get arteriovenous malformations?

The exact cause of AVM formation is not fully understood. While most AVMs are present from birth (congenital), they can also develop shortly after birth or later in life. Although there are instances where AVMs are inherited, it is more common for other inherited conditions to increase the risk of developing an AVM. It is estimated that brain AVMs occur in less than one percent of the general population. However, each year, approximately one percent of individuals with AVMs will experience death directly attributed to the AVM.

Causes of vascular lesions

The exact cause of vascular anomalies in the central nervous system is still not well understood. However, scientists believe that these anomalies primarily occur due to developmental errors during embryonic or fetal stages. Genetic mutations are thought to play a role in some cases, suggesting a genetic basis for certain types of vascular malformations. Additionally, there is evidence suggesting that some lesions can be acquired later in life as a result of central nervous system injuries.

During fetal development, the formation and disappearance of blood vessels are continuous processes as the body undergoes changes and growth. These processes are regulated by angiogenic factors, which are chemicals produced by the body to stimulate the formation and growth of new blood vessels. Researchers have identified changes in the chemical structures of angiogenic factors in individuals with AVMs or other vascular abnormalities in the central nervous system. However, it is not yet fully understood how these chemical changes lead to alterations in blood vessel structure.

Through the study of familial patterns, researchers have identified a genetic mutation on chromosome 7 that causes a specific type of cavernous malformation characterized by the formation of multiple lesions. This mutation is found in various ethnic groups but is particularly prevalent among Hispanic Americans in the Southwest region, who share a common ancestor in whom the genetic change originated. Other types of vascular defects in the central nervous system are associated with larger hereditary medical syndromes, such as hereditary hemorrhagic telangiectasia, Sturge-Weber syndrome, and Klippel-Trenaunay syndrome.

arteriovenous malformations treatment

Diagnosing AVMs

Clinicians often use a distinctive auditory sign called a bruit to aid in the diagnosis of an AVM. A bruit is a rhythmic, whooshing sound caused by the abnormally fast blood flow through the arteries and veins of the AVM. It is similar to the sound of water rushing through a narrow pipe. When the bruit is particularly severe and audible to the individual, it can cause hearing impairment, sleep disturbances, or significant psychological distress.

Various imaging technologies are available to detect the presence of AVMs:

• Cerebral angiography (cerebral arteriography) provides the most accurate visualization of the blood vessel structure in brain AVMs. A contrast agent, a special water-soluble dye, is injected into an artery to highlight the blood vessels, which can then be observed on X-rays.
• CT scans (computed axial tomography) use X-rays to create detailed images of the head, brain, or spinal cord. They are particularly useful in identifying hemorrhage.
• MRI (magnetic resonance imaging) uses magnetic fields and radio waves to produce high-resolution images that can reveal subtle changes in neurological tissues.
• Magnetic resonance angiography (MRA) captures the flow pattern and velocity of blood within vascular lesions, as well as the circulation of cerebrospinal fluid in the brain and spinal cord.
• Transcranial Doppler ultrasound is capable of diagnosing medium to large-sized AVMs and determining the presence and extent of hemorrhage. It assesses blood flow in the brain by emitting high-frequency sound waves through the skull toward specific arteries. The resulting sound wave signals, which bounce back from blood cells, are interpreted by a computer to create an image depicting the velocity of blood flow.

These imaging techniques play a crucial role in the diagnosis and evaluation of AVMs, enabling clinicians to assess the size, location, and characteristics of the vascular anomaly.