Arteriovenous malformations

Basic Imaging Approaches

For detailed diagnosis of suspected vascular anomalies regardless of their location in the body, two main high-tech methods are used. First is CT angiography (CTA), and second is MR angiography (MRA). The latter is especially valuable in situations where it is necessary to avoid radiation exposure for the patient. These diagnostic modalities excel at evaluating the architecture of the arterial and venous components of the pathological vascular nidus. In addition, they make it possible to detect complicating factors such as vascular occlusions or critical stenoses in adjacent territories in a timely manner.

Multiphase scanning and the influence of blood flow velocity

The use of multiphase imaging protocols (multiphase imaging) is directly dictated by the characteristics of local hemodynamics, specifically the velocity of blood movement inside the malformation sac. The behavioral characteristics of blood flow vary greatly depending on the location of the AVM:

• Extremity Anomalies: Blood flow passing through the vascular malformation sac often has a slowed character.
• Brain and Lung Anomalies: For these locations, a pathognomonic sign is rapid arteriovenous shunting (rapid arteriovenous shunting).

It is precisely because of the rapid shunting phenomenon in the brain and lung tissues that the diagnostician encounters an effect where the feeding arteries (arterial feeders) and draining veins (draining veins) are contrasted and visualized on tomograms absolutely simultaneously as early as the early arterial phase of the study.

Ultrafast MRI Technologies

To successfully perform selective imaging of the isolated arterial and venous phases, diagnostic equipment requires exceptionally high temporal resolution. In modern magnetic resonance imaging, this task is solved by introducing specialized ultrafast data acquisition algorithms (ultrafast acquisitions):

1. Key-hole method (k-space sharing / key-hole / k-space sharing): The essence of this approach is that the central zone of k-space, which is responsible for the contrast of the resulting image, is scanned and updated much more frequently than its peripheral part. This significantly saves time.
2. Non-Cartesian forms of k-space sampling (non-Cartesian forms of k-space sampling): More progressive and newer ways of filling the data matrix, allowing for a radical acceleration of the process of obtaining slice-by-slice images.

Clinical Case: Parietal Lobe AVM

An illustrative example is the clinical presentation of a young patient who presented with complaints of intermittent cortical blindness (intermittent cortical blindness). During the examination, an arteriovenous malformation located in the parietal lobe of the brain was diagnosed. The analysis of the obtained tomograms clearly demonstrates the diagnostic value of various modes:

• Axial T2-weighted image (T2-WI): Multiple areas of signal loss (signal voids) are clearly defined in the structures of the right parietal lobe, which is a typical radiological pattern for AVMs.
• Maximum intensity projection (MIP) on time-of-flight MR angiography (TOF MRA): The study confirms the formation of a vascular nidus (vascular blush / vascular blush) and the presence of locally dilated vessels. However, this mode has a serious drawback: due to the dense superposition of a large number of arterial branches on top of each other, it is not possible to reliably identify the primary source of blood supply.
• Axial subvolume multiplanar reconstruction (MPR): This technique overcomes structural superposition and clearly demonstrates the enlarged right posterior cerebral artery (PCA / PCA) acting as the feeding vessel.
• Sagittal subvolume MPR: Additionally reveals the complex anatomy of the afferents, showing that the blood supply comes from two large basins simultaneously—not only from the posterior cerebral artery (PCA), but also from the anterior cerebral artery (ACA) via branches of the pericallosal artery (pericallosal artery).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Evaluation of hemodynamics in the venous component of malformations
• Signs of vascular occlusions in arteriovenous anomalies
• Principles of non-Cartesian k-space sampling in MRI
• Subvolume multiplanar reconstruction (MPR) of the vascular bed

Other topics in the "Interventional radiology" section

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