Use of
Gamma Knife technology for arteriovenous malformations

When an angioma is a congenital malformation in the brain it is also called an arteriovenous malformation. These angiomas can be very small (1 cm) or very big (5-6 cm). One hallmark of this anomaly is that it can go unnoticed for long periods. Initial symptoms may therefore develop at an average age of between 20 and 50 years.

An angioma is usually supplied with blood from one or more small arteries. Through these vessels the blood flows into the nidus (tangle of blood vessels). This constitutes the angioma itself, from where dilated veins drain the blood.

Increased blood flow in the arteriovenous malformation makes the vascular walls thinner, posing the risk of an intracranial hemorrhage. The risk of hemorrhage for patients with an arteriovenous malformation is around 1-4 percent per year. However, symptoms, such as epilepsy, may occur even though there is no hemorrhage.

Many angiomas remain asymptomatic for years, even decades, with the average age for the onset of symptoms between 20 and 50 years.

However, the condition may cause hemorrhaging into the brain tissue, resulting in sudden symptoms such as headache, paralysis, and numbness in limbs. Even a convulsion can be an initial symptom of an angioma.

Angiomas with previous hemorrhaging

We recommend medium-term therapy for all angiomas with previous hemorrhaging to prevent a second hemorrhaging.

Angiomas are generally congenital and environmental influences or trauma play only a minor role.

The diagnosed AVM is initially monitored continually. Where hemorrhaging has already occurred, the aim is to prevent further hemorrhaging. The arteriovenous malformation is surgically removed, collapsed or blocked (embolization) using a catheter. If this is not completely successful, or the treatment risk of such an operation is too high, we can irradiate the arteriovenous malformation with the Gamma Knife. A combination of all three procedures is also possible.

1. Wait-and-see

2. Surgery

3. Embolization using a catheter

4. Irradiation (single-dose radiosurgery)

1. Wait-and-see

In the case of angiomas with no prior hemorrhaging that have also not shown any other symptoms, the options should first be explained to the patient. We explain individually whether and when specific therapy is required.

2. Surgery

Neurosurgical removal of an angioma is always desirable with superficial angiomas that are easily accessible. Removing the angioma prevents hemorrhaging.

3. Embolization (digital subtraction angiography – DSA)

The introduction of a small catheter through the inguinal artery allows collapsing and blocking the angioma. This process is called embolization. In some cases multiple embolizations are required at certain intervals.

4. Radiation therapy

Angiomas have been treated with radiation therapy or over 40 years (single-dose irradiation). The aim of this treatment is to block (obliterate) the angioma in the medium term (after 6-36 months) through the applied radiation dose. This usually works with around 70-80% of treated patients so that the occlusion is permanent, with no risk of further bleeding.

Key factors include:

• The dosage (preferably high-dose region 18-25 Gy single-dose)
• Conformity (maximum dose in the nidus region and minimal dose in the surrounding tissue)
• Selectivity (reduction of the dose in the direct surrounding area of the target volume)
• Accuracy (the radiation exposure and positioning or fixation of the patient)

Effect of the radiation on angiomas / arteriovenous malformations:

The wall of the blood vessels thickens after irradiation over the course of months to years. This procedure aims to block the changed vessels. This process is called obliteration.

However, the vascular wall changes slowly following radiosurgery and it takes several years (usually 1-3) to completely obliterate the diseased vessel.

When using a combined procedure of radiosurgery and embolization, we recommend performing the radiosurgery first. The embolization can also be additionally performed in the case of incomplete obliteration. If you first perform the embolization however, you have to wait at least 4-6 months due to radiation planning constraints to estimate the recanalization processes.

The probability of obliteration depends on the radiation dose; a higher dose provides better and faster occlusion.

For radiosurgical irradiation, the maximum diameter of the angioma should not be larger than 2.5-3 cm. The radiosurgery should normally target the nidus.

The annual hemorrhaging rate is around 2% after irradiation, the same as the spontaneous hemorrhaging rate.

Effect of radiation on an angioma / arteriovenous malformation:

• High-dose irradiation 20-25 Gy
• Angioma (AVM) should be as small as possible (<2.5 cm)
• Occlusion rate after radiosurgery 70-80%, only apparent after 1-3 years

Aftercare

After radiation therapy we recommend regular MRI checkups. Confirmation of a definite occlusion of the irradiated angioma requires a second angiography after around 1-3 years. If the occlusion was not successful, possible options include surgery, embolization, or repeated radiation therapy.

• The radiosurgical treatment of arteriovenous malformations (angiomas) has proven to be a safe, precise alternative to surgery and embolization over the past four decades.
• A superficial angioma should be removed surgically where possible. After all, a complete occlusion can take 1-3 years after radiation therapy. The occlusion rate depends on the radiation dose and is around 70-80%.
• Obliterating the angioma requires high radiation doses (18-25 Gy) that are suitable only for use with small and medium-sized lesions.
• Radiosurgical treatment of arteriovenous malformations (angiomas) is therefore regarded as a safe, precise alternative to surgery for deep-lying and small lesions.