How Doctors Treat Abnormal Brain Vessels With Embolization

Types of Blood Vessels in the Brain

There are organized patterns of blood vessels in the brain. Arteries carry blood enriched with oxygen to brain tissue. Blood is then distributed through small blood vessels and returned to the heart via veins.

An arteriovenous malformation (AVM) is different. An AVM is defined as an abnormal tangle of vessels in which arteries connect directly to veins without intervening capillaries. Because of this abnormal vessel formation, there can be an increased blood flow and pressure in the vascular system.

An AVM can remain asymptomatic for years, although some may produce headaches, seizures, neurological symptoms, or even bleeding. The size, location, and structure of an AVM, as well as how it is supplied, can determine the risk of an AVM rupture and what is the appropriate treatment.

How Do Doctors Lower Blood Flow to an Abnormal Blood Vessel?

Lowering blood flow can be part of the treatment, but does not always require removal of the entire abnormal blood vessel network.

Lowering the amount of the blood supply to the AVM can make a subsequent treatment easier and/or safer.

Microsurgery is defined by the use of many microscopes on the operating field, whereas endoscopy requires only a single microscope. Embolization is actually an endovascular procedure. This means that instead of performing a craniotomy, embolization leans on the vascular system for access.

In the case of embolization, a catheter is slowly advanced through intervention to the required location using imaging. Just as one does in surgery, an embolic material is delivered to the desired location.

In the case of embolization, there is a range of materials used. They include liquid embolic agents, medical glues, or even coils.

The aim is not to completely block blood flow to random locations. Instead doctors use imaging to carefully place the catheter. In this case, the goal is to leave blood flow to the normal brain intact.

After embolization, blood flow is significantly reduced to a specific part of an AVM.

This can change the pattern of blood flow through the malformation. Depending on the anatomy and the treatment plan, reducing blood supply may cause the AVM to shrink in size or become less complex ,p prior to subsequent treatment.

Complete AVM elimination via embolization is possible for some smaller AVMs in a limited number of cases. However, embolization is more often an adjunct therapy.

Embolization as the only therapy is usually preceded by microsurgical resection or stereotactic radiosurgery in the example previously described.

This is commonly referred to as a multimodal therapy.

Why Do Some Doctors Prefer Embolization Prior to Surgery?

AVM's often have an abundant vasculature and a high degree of shunting. This can lead to significant challenges and increased risk during surgery due to the high volume of blood and various directions of flow.

Prior to surgery, portions of the AVM may be treated with embolization to decrease blood flow.

Typically, this is done on a case by case basis, and blood flow may be reduced in order to achieve the following:

• A less vascular AVM

• Less bleeding

• Easier surgery

• Increased safety of procedure

• More manageable surgery

This is often a complementary therapy to surgery. The remaining AVM may require surgery.

Small- and medium-sized AVMs with good anatomy may be treatable with embolization in some cases. Larger or more complex AVMs require additional treatment.

Embolization may be:

1. A sole treatment in certain cases

2. A method of assisting microsurgery

3. A component of a multistage treatment

4. A component of a preparation for stereotactic radiosurgery

Further imaging is necessary to find out if abnormal blood flow exists after treatment.

How Do Doctors Decide Which Blood Vessels to Treat?

In this case, vascular anatomy is critical.

Doctors analyze detailed brain and blood vessel imaging to see:

• the size of the AVM;

• where the abnormal vascular network is located;

• the supplying arteries;

• how the blood drains;

• the AVM's location in relation to different regions of the brain;

• whether that area of the brain has normal tissue;

• whether the AVM is located next to normal brain tissue;

• if there are any difficult to treat characteristics of the AVM.

This information determines the AVM's location for safe placement of embolic material.

Because each AVM has a unique structure of blood vessels, two patients with the same diagnosis can have two very different treatment courses.

Why Does a Multidisciplinary Approach Matter?

Vascular conditions of the brain are complex, and may involve many different specialties.

Neurovascular teams often consist surgeons (neurointerventional and neurosurgical), specialists (neurological and neuroradiological), nursing, and rehabilitation members, who are all able to analyze the patient's imaging extensively to review many different treatment options based on the case.

A good example is collaborative neurovascular care. This illustrates how various specialties can work together to carry out the diagnosis, treatment planning, procedure, and after care. It can be especially useful for collaborative practice for AVM treatment for clinicians considering embolization, microsurgery, radiosurgery, or therapy combinations.

Embolization

Prior to any endovascular treatment, the anatomy of abnormal blood vessels and the pathway of blood into/out of the AVM is comprehensively imaged by the clinician. During embolization, the physician utilizes imaging in order to guide the treatment catheter as well as assess the embolic material being delivered. In this case, the real time surgical view allows the clinician to protect and preserve normal uninvolved blood supply and brain tissue from abnormal blood supply.

Various imaging modalities have expanded the ways that involved specialties are able to access and treat intricate and complicated conditions around delicate brain structures.

For more insight on the role technology has on modern neurosurgical practice, see how skull base surgery evolved with modern technology.

Potential Risks

Like all medical procedures, even embolization has its risks. The risks of the blood vessels supplying the brain include:

• Stroke

• Inadvertent occlusion of normal vessels

• Hemorrhage

• Changes in neurological status

• Injury to a blood vessel

• AVM rupture (in rare cases)

• Need for additional intervention

The risks above can vary due to the location, size, and vascular complexity of the AVM, as well as the treatment approach.

Patients should decide whether to undergo embolization after consulting a neurovascular specialist and weighing the benefits, possible side effects, and alternative treatments.

What Happens After Embolization?

Blood flow reduction is only one step in a many step treatment process for most patients.

After embolization, whether or not blood continues to flow through abnormal vessels and how much of the AVM remains are determined through follow-up imaging.

Depending on the patient’s case and goals, as well as their anatomy, the next step may be microsurgical removal or stereotactic radiosurgery.

Recovery length may vary depending on the treatment. Some patients only need a short period of time after embolization for recovery, while patients who have longer treatments may need more time to recover.

Do All Brain AVMs Need Embolization?

No. Treating AVMs with embolization is often not the only, or even the best option, for some patients.

AVM characteristics such as location, size, blood supply, and the symptoms they cause, as well as whether and how they have bled, and the proximity of the AVM to brain tissue and other important structures are considered.

Some AVMs even require no treatment, whereas others require surgical, radiosurgical or a combination of embolization, surgical, and radiosurgical treatment.

Ultimately, it is important to consider both the abnormal blood vessels and healthy brain tissue.

For brain AVMs, embolization may be done by itself in some cases, but it is usually done as part of a more complex plan. For select cases, embolization can reduce blood flow to an abnormal vascular network, thus making surgery or radiosurgery potentially easier for the patient and the surgeon.

Due to the high degree of variance between AVMs, decisions about treatment should be made after detailed scans are reviewed by a neurovascular team with many years of experience.