AVM (arteriovenous malformation)

Arteriovenous malformation (AVM) is a congenital cerebrovascular tangle that involves a pathological union of arteries, veins and capillaries. Blood vessels responsible for blood supply to an AVM are called feeders, whereas the short-circuit connections are named as nidus.

AVM becomes clinically apparent as a result of hemorrhage in approximately half of cases. Symptoms vary based on where an AVM is located and may include different neurological deficits such as 

• speech
• vision
• movement disorders 

Seizures (37%) and headaches (20%) are also common. In about 10% of cases an AVM is asymptomatic and is detected as a so-called incidental finding.

The classification of arteriovenous malformations is based on the Spetzler-Martin score, which is also important for decisions of treatment.

AVMs often emerge during the evaluation of an acute cerebral hemorrhage using computed tomography (CT) and CT angiography (CTA). They are visible as vascular bundles in the middle or at the edge of the bleeding. AVMs can also be very well depicted on MRI, especially on high-resolution contrast-enhanced MR angiography (MRA). 

The most accurate type of imaging is catheter angiography. Our clinic has the ability to perform rotational angiography, which provides precise three-dimensional images. It enables clear delineation of the AVM architecture and is the basis for planning the further therapeutic steps.

The clinical management of an AVM (necessity of treatment and type of therapy) depends on many factors.

Treatment of an AVM is necessary in the case of bleeding. Acute, large symptomatic bleedings often require emergency surgery to remove the bleeding and, if possible, the entire AVM. But even in case of minor bleeding, an AVM should be treated because the risk of rebleeding in ruptured AVMs is high. 

If an AVM is diagnosed by an epileptic seizure or as an incidental finding, the further management depends on a number of factors, which are assessed in an interdisciplinary approach. Localization, size and individual vascular architecture of an AVM are significant factors. 

If the localization of an AVM is very complex, it may be preferred not to perform any treatment at all because the risk of bleeding and clinical deterioration without therapy may be statistically lower than with treatment. In these cases, an AVM should be annually controlled by MRA.

If there are indications for the treatment of an AVM, three therapeutic options are available: 

• microsurgical resection
• endovascular embolization
• radiation therapy

The main objective of any therapy is always the complete closure of an AVM. Partial closure is not effective because it does not eliminate the risk of bleeding.

If the AVM architecture and location allow for a low risk operation, full microsurgical AVM resection is the treatment of choice. This eliminates the risk of spontaneous bleeding in the future. 

Surgical planning is based on detailed imaging. Three-dimensional MRI data (MRA, MRV, fMRI, DTI) are fused with data of catheter angiography to accurately assess the AVM feeders and draining veins in relation to nidus. 

In addition, the intra-cerebral location of an AVM with respect to surrounding functional areas, white matter tracts and surgical corridors are stereoscopically visualized in a Virtual Reality simulator. The combination of this information allows accurate planning of the operation. 

ICG angiography (with the fluorescent substance indocyanin green), sonography and catheter angiography are available for resection control during surgery. In most cases electrophysiological monitoring of the brain is also used. The combination of these techniques significantly minimizes the risk of surgery and facilitates complete AVM resection.

In many cases, especially in cases of large AVMs, interventional radiologic occlusion (embolization) of feeders prior to surgical resection is possible. Sometimes it is also possible to completely embolize an AVM; this often requires more than one embolization procedure.

Focused radiation therapy (radiosurgery) may be useful in cases of AVMs, which are small and difficult to access. Radiation causes destruction the vessel walls which leads to thrombosis and closure. The risk of spontaneous bleeding does not decrease immediately after irradiation and overall the chance of complete AVM occlusion with radiation is approximately 80%. 

After radiation treatment it usually takes up to three years for an AVM to be obliterated.

54-year-old female patient with auditory hallucinations such as water and wind sounds over the course of 9 months. The MRI / MRA showed an approx. 2 cm large AVM in the upper gyrus of the temporal lobe, in the center of the primary auditory cortex. The feeding arteries from the right middle cerebral artery (MCA) were well visualized, the venous drainage was localized superficial to the sigmoid sinus. 

Due to the easily accessible location, microsurgical resection was the first choice of treatment. The operation was carried out without complications. Intraoperative catheter angiography was performed, which confirmed complete resection. 

The patient was discharged home without any deficits five days after surgery. The auditory hallucinations resolved completely within a few postoperative days.