From the Guidelines
An arteriovenous (AV) malformation is a direct connection of artery to vein via abnormal dilated vascular channels without a normal intermediary capillary bed, resulting in a high-flow shunting of blood. This condition is characterized by an abnormal connection between the high-pressure arterial system and the low-pressure venous system, leading to vessel weakening over time and potentially causing rupture and bleeding 1. The abnormal dilated vascular channels are known as the nidus, and the true incidence of brain AVM is unknown, although asymptomatic prevalence on MRI is estimated at 0.05% 1.
Key Characteristics of AV Malformations
- Direct connection between arteries and veins, bypassing the normal capillary network
- Abnormal dilated vascular channels, known as the nidus
- High-flow shunting of blood, leading to vessel weakening and potential rupture
- Can occur anywhere in the body, but most concerning when located in the brain or spinal cord
Symptoms and Treatment
Symptoms of AV malformations vary depending on location, but may include headaches, seizures, muscle weakness, vision problems, or neurological deficits 1. Treatment options include surgical removal, endovascular embolization, stereotactic radiosurgery, or a combination approach, with the best treatment depending on the malformation's size, location, and the patient's overall health 1.
Risks and Outcomes
Without treatment, AV malformations carry a risk of hemorrhage, which can cause stroke, disability, or death, particularly with brain AVMs, with an annual rupture risk of 1.3% for previously unruptured AVM and up to 4.8% for previously ruptured lesions 1. Imaging findings associated with higher hemorrhage risk include intranidal aneurysm, deep venous drainage, deep location, or venous outflow obstruction 1.
From the Research
Definition of Arteriovenous (AV) Malformation
- An arteriovenous malformation (AVM) is a vascular lesion that arises from congenital errors during development of vessels, resulting in abnormal connections between arteries and veins 2.
- AVMs are characterized by a tangle of dysplastic vessels (nidus) fed by arteries and drained by veins without intervening capillaries, forming a high-flow, low-resistance shunt between the arterial and venous systems 3.
- AVMs can occur anywhere in the body, but most develop in the brain or spinal cord, and extracranial or peripheral AVMs have a predilection for the head, neck, and limbs 2.
Characteristics of AVMs
- AVMs are abnormal connections between arteries and veins, bypassing the capillary system 4.
- They can be asymptomatic, but may cause significant morbidity and mortality due to the risk of bleeding or other complications 5.
- The size and location of AVMs can vary, and they can be classified into different types based on their characteristics, such as fistulous lesions in children and nidal lesions in adults 3.
Pathogenesis of AVMs
- AVMs were long considered congenital, but recent findings suggest that they may arise from aberrant vasculogenesis, genetic mutations, and/or angiogenesis after injury 3.
- Inflammation is associated with AVM genesis, growth, and rupture, and may play a role in the development and progression of AVMs 6.
- The exact mechanisms of AVM pathogenesis are not fully understood, and further research is needed to develop effective therapeutic strategies 5.