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What Is Brain AVM?

Overview

A Brain arteriovenous malformation (AVM) occurs when a tangle (like a ball of wires) of arteries (which are designed to carry high flowing blood coming from the heart) connects directly to veins (which are designed to carry low flowing blood slowly back to the heart) without any capillaries (the smallest type of blood vessels, thinner than a strand of hair) which are suppose to be in between arteries and veins. Arteries, being high flow, should never connect directly to veins, which have a low flow, as it puts excessive pressure on the vein walls. Without capillaries, which reduce blood flow pressure, the high-pressure blood from the arteries causes the veins to weaken over time, potentially leading to vessel rupture and a brain bleed.
 

What is an Aneurysm?

An aneurysm is a weak spot in a vessel wall that develops a blood-filled sac in the wall of the blood vessel. An aneurysm rupture is when this sac can no longer sustain the pressure of the blood and tears, causing blood to leave the vessel and enter into the surrounding brain tissue. When blood enters the surrounding tissue of the brain, it is a called a hemorrhagic stroke. This causes damage to the surrounding brain tissue because blood and brain tissue are never suppose to mix directly. 

What is a Stroke?

There are two types of strokes:

  1. Hemorrhagic: Hemorrhagic strokes make up 13% – 15% of all stroke cases and 50% of pediatric stroke cases. They are caused by a weakened vessel that ruptures and bleeds into the surrounding brain. The blood accumulates and compresses the surrounding brain tissue.
  2. Ischemic: An ischemic stroke occurs when the blood supply to part of the brain is interrupted or reduced, preventing brain tissue from getting oxygen and nutrients.
 
The grading system is based on a scale of one to six, with higher grades indicating greater complexity and higher risks.
 
Grade III – VI AVMs may require a combination of treatment modalities or conservative management. The higher the grade of AVM, the greater the complexity and risk for treatment.

The Spetzler-Martin Grading System

The Spetzler-Martin grading system is a widely used and essential tool in the evaluation and treatment planning of brain arteriovenous malformations (AVMs). Developed by Drs. Robert F. Spetzler and Albert R. Martin in 1986, this grading system provides a standardized and comprehensive approach to assess the complexity and risk associated with AVMs. It helps healthcare professionals determine the appropriate treatment strategy for each individual patient, taking into account factors that influence the potential risks and benefits of intervention.

Brain AVMs are abnormal tangles of blood vessels in the brain that disrupt the normal blood flow. They consist of a complex network of arteries and veins that are directly connected, bypassing the usual capillary system. The significance of AVMs lies in their potential to cause serious health complications, including bleeding into the brain, seizures, and neurological deficits.

The Spetzler-Martin grading system assigns a score to each AVM based on specific characteristics, such as size, location, and presence of eloquent brain regions (areas responsible for critical functions like speech, motor control, and vision). The total score obtained from these characteristics provides an overall measure of the AVM’s complexity and associated risks. The grading system is based on a scale of one to five, with higher grades indicating greater complexity and higher risks.

The Spetzler-Martin grading system serves as a valuable guide for neurosurgeons and interventional neuroradiologists when deciding on the most appropriate treatment approach for an AVM. Grade I and II AVMs are usually good candidates for either microsurgery or endovascular embolization (a minimally invasive procedure to block blood flow in the AVM). Grade III AVMs may require a combination of treatment modalities or conservative management. Grade IV and V AVMs, due to their complexity and high risks, often demand a more conservative approach, focusing on symptom management and preventive measures to reduce the risk of bleeding.

It is crucial to emphasize that the Spetzler-Martin grading system is just one of many factors that healthcare professionals consider when planning treatment for an AVM. Individual patient characteristics, medical history, and personal preferences are also essential in determining the best course of action.

Illustrations of the nine AVMs in the Supp-SM grade 6+ subtype. A higher proportion of older patients with larger Supp-SM grade 6 AVMs (S3A3, S3A2, and S2A3) had neurological deterioration, compared with other patients with Supp-SM grade 6 AVMs. Thus, surgery is less favorable for older patients with larger Supp-SM grade 6+ subtype AVMs. From Catapano, J. S., Frisoli, F. A., Nguyen, C. L., Labib, M. A., Cole, T. S., Baranoski, J. F., Kim, H., Spetzler, R. F., & Lawton, M. T. Intermediate-grade brain arteriovenous malformations and the boundary of operability using the supplemented Spetzler-Martin grading system. J Neurosurg. 2022;131(1): 125-133. [https://doi.org/10.3171/2020.11.JNS203298] Modified from Spetzler RF, Ponce FA. A 3-tier classification of cerebral arteriovenous malformations. J Neurosurg. 2011;114(3):842–849 and Spetzler RF, Martin NA. A proposed grading system for arteriovenous malformations. J Neurosurg. 1986;65(4):476–483. Published with permission.
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