Cerebral arteriovenous malformations

Computed tomography and magnetic resonance imaging

Initial evaluation of patients with suspected neurovascular diseases often begins with basic tomographic imaging techniques.

• Non-contrast brain CT: A lobulated hyperdensity is visualized (lobulated hyperdensity). Focal calcification sites (e.g., in the parietal lobe) are characteristic. Parenchymal hemorrhage may be absent.
• Contrast-enhanced CT: Pathological vessels demonstrate intense contrast enhancement (avid enhancement). The identification of multiple AVMs in different brain lobes suggests hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu disease).
• Brain MRI: Details large superficial draining veins and diffuse brain tissue changes. An important finding is the identification of large flow-related aneurysms (flow aneurysm), which are often localized in the terminal portion of the internal carotid artery.

Digital subtraction angiography (DSA)

The method is recognized as the gold standard for assessing the complex angioarchitecture of vascular pathologies. On the angiogram, an AVM has a distinct structure:

1. Afferent part: Blood supply is provided by feeding arteries (often branches of the middle cerebral artery).
2. Compact core: A pathological vascular tangle (nidus).
3. Efferent part: Venous outflow occurring via the superficial and deep venous systems of the brain.

Performing vascular imaging is critical for detecting treatable pathologies. For example, in arteriovenous fistulas, DSA reveals connections between branches of the external carotid artery and dural venous sinuses, as well as pathological retrograde blood flow (e.g., via the vein of Trolard). Fistulas are successfully treated endovascularly using liquid embolizing agents.

Differential diagnosis: Cavernomas

Cavernous angiomas (cavernomas) have a specific appearance on magnetic resonance imaging that differs significantly from AVMs:

• T2-weighted images: The lesion has the classic «popcorn» appearance ('popcorn' appearance). A dark peripheral hemosiderin ring is defined around the lesion (peripheral haemosiderin ring).
• T1-WI and T2-WI: Areas of T1 shortening corresponding to blood degradation products at various stages are visible.
• SWI sequence: Is the most sensitive. Due to the paramagnetic properties of blood, a pronounced «blooming» artifact occurs (susceptibility 'blooming'). This sequence is indispensable for detecting small multifocal cavernomas invisible on standard projections.

Chronic hematomas and low CSF volume syndrome

Diagnostic imaging also plays a key role in detecting secondary fluid and blood collections.

Chronic subdural hematomas appear on CT as flat, bilateral, convexity collections. The appearance of an area of increased density within the hematoma indicates fresh bleeding (acute component). FLAIR MRI clearly visualizes the encapsulated (multilocular) nature of the hematoma and local mass effect—sulcal effacement (sulcal effacement).

Low CSF volume syndrome (Low CSF volume syndrome) develops after strenuous Valsalva maneuver or lumbar puncture.

• Clinically: postural headache (worsened by standing).
• Pathogenesis and MRI: brain descent occurs (brain descent) along with mild cerebellar ectopia. Diffuse dural thickening is noted (well visualized on FLAIR and contrast-enhanced T1). Flat subdural fluid collections may be present. The changes regress after treatment.

Class and exam questions

What else to study on this topic

• Angioarchitecture of venous drainage: veins of Trolard, sagittal sinus
• Arteriovenous fistulas: formation mechanisms and endovascular embolization
• MRI semiotics of hemoglobin degradation (T1 shortening and susceptibility effects)
• Pathophysiology of low CSF volume syndrome and the Valsalva maneuver

Other topics in the Neuroimaging section

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